Primitive Archer
Main Discussion Area => Bows => Topic started by: Badger on January 26, 2008, 04:43:38 pm
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Thought I would do a building by mass buildalong as the tb4 will be comming out soon with a chapter dedicated to this. This particualr bow will be a 50# 65" long boo backed osage, It will have a 10" stiff handle and fade area and initial glued in reflex will be 2". Tiller will be slightly elyptical with stiff outer limbs. Hopefully when the bow is finished it will maintain about 1" reflex. Projected mass for this bow will be about 22.5 oz. Including the glued on handle, Mass was projected as follows.
65"=5.5oz
2" reflex=1oz
12" stiff handle and fade=6oz
draw length 30"=1.75"
50#=10oz
You will notice that the numbers I used to calculate don't match the numbers I was going to use to build the bow. A slightly elyptical tiller will equate to a longer handle and fade section and a stiff outer limb equates to a longer than actual draw length because the inner limbs have to bend more to make up for the stiff outer limbs. The draw length figure works off a ratio of working limb to draw length and I will explain this is I go.
Tomorrow I will rough out the bow and glue it together. I will be looking for the rough glue up to weigh around 28 oz, about 6 oz for the boo and about 22 oz for the belly stave. Hopefully if weather permits I can tiller it out on monday. Steve
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Thanks Steve, this is a great idea. I will be watching close. Maybe when you get to tiller you could show pictures of a couple of bows and explain the tiller and how it adjusts the length of the riser in the formula a little more. Justin
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What Justin said :) Pictures of the tiller will also help.
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I have been interested in your formula but it seems a little difficult for me to fully understand how to use it. Maybe seeing it done will help.
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This is great Steve, a step by step would help me too.
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I'm watching and following closely. Please give us as much info as possible. I think you are on the cutting edge on the formulas, so please explain as much as you can. Jim
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Really looking forward to this one Steve. I read your earlier post explaining the formula with great interest. I love it when science and art get together.
Red Dwarf
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I am really glad there is some interest. I hope to be able to show some of the more practical uses for the formula. I wouldn't expect that everyone would be running back and forth to a scale as they build their bows. I hope the weather holds up so I can get started tomorrow but in the meantime I want to go over some of the practical ways it can be used even if it isn't something someone might want to incorporate into their everyday bow building. Optimum mass can be established using sound tillering tecniques and monitoring the bows set and signs of wood fatigue. But these same tecniques will not always tip you off if you have a piece of wood that is still a bit high in moisture even if it appears dry. The mass formula will tip you off before you get very far. It will also tip you off if you have a design that is bad, either underbuilt or overbuilt before you get too far. I think most importantly it simply gets a person thinking about his design and his demensions and how they relate to each other. From a logical standpoint if a man likes his bows in a nice perfect arc of the circle tiller and bending right out of the fades the only design that will really come into target mass would be a pyramid or very close to a pyramid. This is simply because if wood is bending the same it should be the same thickness. I look at the width of the bow the same way i look at the governor on a diesel truck, the thickess determines how far a piece of wood can bend and the width determines how far it will bend.
Just for instance, lets say i was going to make a 55# bow, 8" handle and fades and a simple attractive even tiller throughout. The mass would project out as follows'
length-66"= 6 oz ( .5 oz for every 1" past 54")
tip set back-0=0oz ( 1oz for every 2" set back)
handle and fades-8" = 4 oz ( 1oz for every 2")
draw length-28"= -5 oz ( add.5 oz for every 1" of working limb less than draw length)
figured as follows, 66" bow - 8" handle=58" working limb divide that by2=29" working limb for a 28" draw so take away 1/2oz.
Draw weight-55#=11oz ( 1 oz for every 5# draw weight)
total would be about 20.5 oz
girl friend is calling be back in a while LOL.
i
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"Girl friend is calling' It's good to see you still have your priorities straight Steve :D.. By weighing some of your existing bows and comparing the weight to Steve's formula will give you a good perspective since there will be a corelation between how it performs and the actual mass.
Steve's formula really put numbers to the "traditional " definition of a bow being overbuilt and underbuilt. When Steve came out with this formula I weighed all the bows I had, and my personal bows were all underbuiilt which is what I had expected. I had been weighing my bows for years, but never had anything to really compare the numbers to other than how fast the bow shot..Now I know exactly where I am with a bow well before shooting it.
Rich-
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There's always interest in your threads Steve.
This is an excellent method for new bowyers to learn how to impove the performance of their bows quickly.
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Both Mark and Richard are known for successfully making some of the lowest mass bows you can imagine. Marks heat treating and how it affects mass can be a topic of it's own, and Richards work with bamboo and heavy tropical woods is a great example of how properly matching the belly to the backs can produce extremely low mass bows. It's funny that both of these guys just replied because I used samples of both their bows when fine tuning the formula. Richards bows will often have a slight flex in the handle area that he strategicaly takes advantage of by making his limbs scary narrow but still stable. On the bows I have looked at made by Mark he has trimmed all the fat and gotten the limb working close to the fades for maximum energy storage allowing him to keep the outer limbs narrow and light. They still fall below projected mass figures but I attribute that to just pusing the limits a bit. I have another 1 1/2 hours before daylight so I figure I will just get some stuff layed out waiting for the sun to come up so I can work, Steve
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Good stuff, Badger. This is a board bow? Jawge
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Jawge, it will be an osage board backed with bamboo. maybe i will do a stave of mulberry while the bow is drying. Steve
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Steve
Noticed that the formula that you are using for this build along is a little different from that in the "How To" section. Is this because this will be a backed bow or just evolution/refinement of the formula itself?
Red Dwarf
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Red, I will have to go back and look at the formula in the how to section, there are two floating around and one is incomplete. Steve
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Inbetween the rain I am working on the bow here is where I am at so far.
Picture#1 is showing the mulberry stave and the osage boo parts i will use for the 2 bow build along.
Picture#2 shows the guide I use to run my bamboo through the bandsaw for it's initial thinning
Picture# 3 shows me running the boo through the bandsaw.
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Here are a few more pics,
#1 is just tracing the boo to match the roughed out belly stave
#2- the belt sander I flatten everything on before glue up
#3- The slices I cut off the belly I reused on the handle
#4- Total mass at this point is 32 0z, I actually lightened it a bit more on sander before glue up so it is now actually 27 oz.
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Here is the glue up, I use tightbond 3 and bicycle innertubes. I like to leave a little gap inbetween each wrap. It has to be pulled very tight to get the deflex reflex as you see here and in the middle of the limb I will ofyen have to make several wraps just to get it pulled down. I will let it dry in the house and in the morning take the wraps off and clean it up a bit, I will take it to floor tiller but wait one more day till I strat really stressing the bow as it has been pretty wet lately and the glue may not cure strong enough overnight. Steve
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Ingenious little jig for trimming the bamboo Steve... This rain is driving me nuts!
Rich-soaked
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The mass formula in the how to section is wrong! I didn't know it was there. It doesn't adjust for working limb in relation to draw length at all. maybe I cna get them to remove it. Steve
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I deleted the mass theory thread in the How To section Steve, Being as you started the thread you also could have deleted it.
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Steve I will repost your excel spreadsheet so its readily available for folks.
I believe you said this is correct.
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Thanks Dana, I use the calculator so much I almost cant remember how to figure it with out it anymore.
I am also working on the mulberry stave, yesterday I reduced it and took off the 3/4" thick sapwood, The stave looks good and I will see how it comes out as a broadhead shooter for flight. So It will finish as follows, 68" long 50# at 27", I will likely set the tips back just a smidgeon. So I will be looking for a finish weight of about 19 to 20 oz of mass. I am debating wether or not I should drop the weight on the boo backed bow to 50# and use it for flight as well. I really like the way it is looking when I took the wraps off this morning. If I do drop it to 50# it will just come in around 1 oz lighter than I projected. With backed bows I figure about 10% less mass than stave or board bows but this one here has a heavy handle section so should come in about the same. Steve
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Badger, I just realized that you have a chapter in TBB4. You must be pretty excited! ;D I can look forward to pointing to the book and telling my family, "Hey, this is one of my friends on the internet!" I've been borrowing a friends copies of volume 1 and 2 for about a year, so I hope to return them and buy the complete set.
One question... Did you thickness taper the osage lam before glue up?
Jim
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Jim, I don't really thickness taper it, I just tim it to abpot a 3/8 thickness, noraMLY I tiller the limb a bit but when they are side tapered limbs they are pretty much tillered allready with even thickness. In a few minutes I am goig to go outside and clean the glue off and get it to floor tiller. Post some more in about an hour or so, Steve
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Photo 1 is present weight after cleaning up and floor tillering, shaping handle etc. Weight is 23 0z, target weight is 22 oz so it looks like I am right on target. I was hoping it might be just a tad further off so I could show how using the sides to adjust weight actually works.
Photo 2 is right out of the rubber bands, weight was 29 oz instead of the 27 I mistakenly posted yesterday.
photo 3 is glueing on some osage tip overlays
photo 4 is shoing how the reflex will often increase durring floor tillering, in this case from 1 3/4" to 2 3/4".
Going to let it sit till tomorrow morning before completing the tillering.
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Might as well talk about tillering while I am waiting for the glue to cure. This year I started using the long string method of tillering a bit but got back away from it. I still use the long string for a couple of things. The long string is a good way to tell at what weight your bow is at for a given draw length. It is also a good way to tell if you fades are going to bend too much for the weight of the bow you are building, this is particualry useful for glueups. The look at your tiller on r/d bows especially is too misleading on a long string to be of much value. Now days I simply sight down the limbs looking at the bend of each limb as I floor tiller and then right before I go to brace the bow I hook it up to a string about the same length as the bow and pull it to full draw weight, when I am with in 4" of full draw weight with a long string I go a ahead and brace it. I then hold the bow on my lap braced and use a scraper to get both limbs looking the same at brace, excercising it inbetween scapes. Once the braced tiller looks good i proceed to the tiller tree to finish it off at final weight. Every time I pull the bow an additional inch of draw length I note before that pull the draw weight at a lower drawn length, after the pull to the new longer length I go back and check the weight at that lower draw length and see if it changed, if it changed the bow is picking up some stresses and the wood is fatiquing, tipping me off to getting some more wood bending usually near the fades. The particualr bow I am working on right now has more reflex than I actually wanted but at the same time I don't like to reduce reflex by breaking a bow down too much. I will try to limit the set the bow takes to less than 1 1/4" giving me a net reflex of about 1 1/2". I like to look at every bow as potentialy the best or fastest bow I have ever built, this keeps the adrenalin flowing until the bow is actually tested. Steve
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Nice build along Steve. I like the simple guide you use for thinning the Bamboo.
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I like that guide also. I will have to try it. I've been using a 12" disc sander and did not like all the dust.
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Eddie, it will take me about 2 times as long to run a clean growth ring on the mulberry stave than it will to finish this whole bow. I just about have it ready to start tillering. I have about 1 1/2 hours invested in the glue up so far and about 4 hours into running a ring LOL. I still prefer the stave bows by a big margin. steve
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Nice build along Steve,Looks like you are coming right along.Lots of calculating there,
looks like a job for GregB.He like that kind of stuff.I should do more of it just don't seem
to take the time.Thanks for sharing. :)
Pappy
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Pappy, I know it's not for everyone but really not as much calculating as it seems to be. I know that you make a lot of different style bows kind of like me. I make all different draw weights, all different styles from all kinds of woods. The last couple years jut to test this out I have been making them from 35# to almost 160# and from 48" long to 88" long. It's main purpose is to make sure you have enough wood to complete a design, and it will also suggest designs in a lot of cases. If you are making the same kinds of bows from the same kinds of woods it would be of little value. I can tell you one thing for sure I come up with a lot different demensions than I often see posted as suggested starting places, I also am a lot more comfortable now making longer bows, I use the formula to help me decide on a tiller shape for the long ones.
Would anyone like to post some full draw pics of some of their bows here, just give the length of the bow and the draw weight with a full draw pic and we will do a mass breakdown on it? Steve
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Pignut hickory, 58 ½” NTN, 42#@25”, 1 ¾” at fades straight taper to 5/8” at nocks. Has 1” of string follow after unbracing. Buffalo horn and bone tip overlays, black cordage handle wrap.
Steve I will weigh it tonight, I have an old nail scale which seems to be pretty accurate
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Nice looking bow Dana. :) Looks cold up there. ;D ;D
Pappy
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Thats yer hickory pappy and ya its cold and we have blizzard warning for later today >:(
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Dana, for that bow and tiller I would have used stright limbs to about mid limb. It's is pretty stiff out of the fades so I would call the center handle and fade area 10" instead of 8". Total mass projected would be a little over 16 oz and set would be about the same as you have hopefully at 1".
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Dang I'm going to have to run home at lunch and weigh it ;D Do you add any weight for tip overlays or are they negligible?
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Dana, I never add on for overlays, your draw length was just about right for that bow length and handle design and it only added about 1/3 of an ounce for draw length. if you draw length was 28 the mass would have gone up to 17.5 oz. Steve
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I couldn't stand it I went home and weighed it, with the string and grip it weighed 17.5oz, badger I did tiller it out to 26"
as its going to a green horn and I want a little insurance. I also induced about 1.5" of reflex at the floor tiller stage does that affect the calcs?
I'd say I came pretty close to what your mass theory says it should be. This bow spits a 450g arra pretty dang good.
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Dana, thats pretty cl;ose. Thats the whole idea, it realy doesn't hurt to be a little hevy on the inside limb as long as the last several inches aren't too bulky. Now if you would have stopped and weighed that stave early on and found it only weighed 15 oz instead of 17 you could have mad a little adjustment by getting it bending more near the fades and still come into weight ok with out taking set. Steve
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thanks Steve this was edumakational, I'm going to have to keep the scale handy as I see the value of your theory.
You said with this tiller you would have kept the limbs straight to mid limb care to explain.
I hope in TBB 4 you go into limb shapes and designs with type of tiller, with pictures of course.
Some one else's turn to post a bow to be examined :)
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Did a little tillering this morning, ran into a minor problem which is good for the buildalong but bad for me LOL. The bow keeps adding reflex as it is tillered, now right at about 4" which is way more than I like. This also raises the amount of mass I need in the stave. Normaly on a boo backed osage I will take allow myself about 10% mass less than what the formula calls for but right now I am at 20 oz. Not much wood will need to come off now as I am pretty close to final tiller but I am allready below the weight I wanted to be at and starting to worry if it will be able to take the extra strain. I have decided to get it working a bit further out to the tips and a bit closer to the handle, more working limb will allow me to build the bow lighter. I don't like to loose reflex in tillering i would prefer just to build it with less reflex and keep what i put in originaly. I think I rushed a bit for the buildalong and didnt take the belly stave down enough and as I remove wood the bamboo cantinues to pull it back into more reflex, I will probably stop the bow at 27" draw now also but still keep my 50#. Hopefully the bow will maintain 3" reflex when finished. This is where I have a lot of fun. I know the bow is a bit overstressed but if I do my job right it will come out hot!. Looks like she is going to finish at 19 oz, so I am going to go back to my formula, play with the numbers and make a final descision as to what she should look like when done.
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I went ahead and braced her up picure is 1st brace and then went ahead and pulled her out to 50# which she hit at 24". right limb is just a tad stong and left limb needs a few scapes and she should be done. Bow has a super smooth draw buildng at less than 2 1/2# per inch of draw. Very high early draw weight. reflex dropped to 3" which pleases me greatly, likely will drop another 3/4 inch or so as I hit my 27" draw. Looks like she will finish at 20 oz, a little ighter than I wanted but if she hold together it will be a good thing.
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The center limbs look stiff, but compared to the unbraced profile they are actually working quite a bit. I cut the tip of my middle finger off a few days ago so I won't be able to shoot the bow till the finger heels. Steve
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Ok, just got her finished up at 52# and 27" she held 2 3/4" reflex and feels like a good shooter. I will get her sanded up and finshed and try to post a finsihed full draw in a couple of days. i used a little more bend in the inner limb than I had originaly planned to make up for the lower than planned mass, looks like it worked out ok. Steve
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I cut the tip of my middle finger off
Nice buidalong but geez... :o go easy on them body parts!!! ;D
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Kinda looks like my new glass bow form with all that reflex--might be a really fast. :o
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Dang Steve, You make it look easy. What's with the missing digits? :o
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I'll give you a quarter to see your finger.
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And another quarter to evaluate this bow.
57" n/n, 52lb@28", 409g = 14.5oz., the handle is 4" and its slightly skinnier and thicker but not a real stiff handle. Maybe 6" of handle/fades area but there is some bit of bending I think.
I tried to do my favorite osage longbow but it is slightly heavier than my triple-beams will weigh (over 620g) and when I went to double-check the poundage (should be 60lb) the rope on my tiller tree broke. So it will be delayed.
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Good looking weapon!! Nice tiller, too. Hope it shhots as well as it looks!
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Lennie, I like the tiller you used on that bow, great tiller for a short bow. little extra bend near the fades. I would have figured that bow at about 15.5 ounces and allowed for a 6" handle and fade area. With the tiller you used bending more near the fades, using a 4" handle and fade figure would have worked just as well giving you what you have at about 14.5 ounces. Steve
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Glad to hear its about right. This one was a little unusual in that the handle area is kind of in between full working and stiff. Glad to hear it isn't terribly overbuilt. Didn't think it could be but it really held its side profile so I wondered.
Wulamoc thanks, it shoots fine and I like the looks. I don't remember exactly when I made it, within the last year I'm sure. It just surfaced out of the barrel when I was showing my friend different styles of bows. This one would make a decent little turkey bow to be shot from a sitting position. You don't really have enough handle to put your whole hand on it, I just rest the web of my hand on the center of the handle so I have a little room for the arrow to pass through in the narrowed area.
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Here's another one. This is the bow my friend built for me. Its a true bendy handled bow, pronounced R/D profile, 56" n/n, pulls 50lb@28", and weighs 473g=16.7oz.
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Lennie that last bow I would call a little overbuilt, I would have built it at about 12 oz. What kind of wood is it? Steve
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Badger and tom sawyer, nice bows. Badger, don't let the pressure of a buildalong get to you. Gotta watch those fingers. Jawge
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Lennie, the first one is really nice-looking. I'm heading in your direction today, going to a funeral in Vandalia. Hope to get home before the snow hits.
Badger, It is interesting to see how the mass formula comes close to already finished bows--a good test for sure on these bows that are extremely well made. I'm sure that the bow material is a factor. You mentioned a conversion factor for the bamboo backed bow. Have you found a need for other conversions due to materials and/or laminates, etc? Jim
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Jim, on any wood backed bow I give myself a 10% less alllowance. I call it the perry reflex factor. I don't make any allowances for different woods but do often find that yew for instance tends to come in lighter. Very dry wood will also come in lighter. The big trick to using the formula in learning how to apply a figure for stiff handle and fades. For instance if you were making an elb bow and the center 16" were semi stiff bending 1/2 as much as normal you might use a figure of 8" for stiff handle and fades. Some people figure the formula is good for begainers but I actualy think it is more for advanced work.
Jawge I did the finger at work LOL. for some reason when he sewed it back on it looks longer now than it was. just a bit crooked on the tip. Steve
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Steve its osage. I kind of expected it would be a little overbuilt, you'd want that if you were making a bow for someone. He also made a few areas with pin knots a little wider, I wouldn't have done that myself but it really gives the bow some extra character. I think he was trying to avoid getting a pin too close to a limb edge. Also, the tiller probably could have been rounded up just a bit. The bow has some reflex but it is fairly mild. Thanks for the review.
Jim I heard we might be getting 1-3", up to 6" farther south. Be careful. You'd be welcome to stop for a visit but I'll understand if you pass. I get off work at 5.
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Lennie, the formula is pretty conservative with its mass. Often with dense woods like osage you run into a situation where no matter how narrow you make it the mass is still to high, this is when you start to stiffen the handle area for a higher projected mass. It works. I would almost bet that bow has handshock. (almost) Steve
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That first bow I posted was also osage. And I honestly don't find the second bow to have hand shock at all. Thats a subjective thing though.
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Some people figure the formula is good for begainers but I actualy think it is more for advanced work.
You're probably right Steve. A lot of guys that have been making bows for many years are satisfied with the bows they make even though they no doubt can be improved on. Beginners are the ones more likely to use the formula though and in so doing make huge improvements in their bows mainly because they have no preconceived notions and are starting out with an open mind.
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Marc, you said a mouthful. As a beginning primitive bow maker, I agree 100%. You guys who have made many, many bows from many different woods have an advantage. I've only made one selfbow, so I have no preconceived notion, except from my many years of making glass bows. Big difference. To be honest about it, I'm also looking at the mass formula from the perspective of improving my glass designs. Many glass bow makers including myself often get bailed out on a bad design due to the forgiveness and strength of the glass. I'm trying to overcome that. A good bow is a good bow...lol. Jim
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Can you imagine all the knowledge of bow makeing that could have been shared 10 years ago without the internet.
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I think the internet has given us 10,000 years of advancement in bowmaking. One thing I laugh about a lot. If joe shmo has a great idea about bow making and shares it with us online within one week the whole world knows whay he knows. A lot of guys are just blessed with a natural feel for the art of bow bowmaking. Before the internet I htought I was the only one in the world who made wooden bows, I struggled like crazy for a few years. 2 weeks after I got online I was making bows that worked. Jim, I think it is really cool that glass bowyers and wood bowyers have started sharing design ideas, I imagine when glass firt came out they did the same thing and then went seperate ways. Everything went to glass recurves. The long bow is making a big time come back in traditional archery. Both modern and primitive. Good stuff happening right now. Steve
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I am actualy working on another one right now, this time an elb, I glued it up this morning and will clean it up tomorrrow and start tillering. The only two set ctiterias I have are draw length and bow length. I am going to let mass dictate the tiller and the poundage. I will do it as a buildalong. It is bamboo, maple core and mora belly. The raw glue-up weighed 30 oz, belly is allready rounded, tomorrow I will shape it like an elb and clean it up and I imagine the weight will drop to about 25 oz and from that point I will see where it steers me. An 80# elb with a semi stiff handle section should come in around 22 oz, this will likely be what I go for. Steve
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"Daddy, all your bows look the same." That's what my daughter said once. LOL. I always tried to involve my daughters in bow making for various reasons. I guess I'm not that open minded regarding trying different things. :) Jawge
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Jawge, you are like a rock in our bow building community. You show people how to build good solid bows using sound proven principles. Ane then you have that science background behind you to seperate the bs from the good stuff. Good mix! Steve
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Thanks, Steve, for the kind words. Jawge
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Great info Steve, Thanks for sharing. You are definately the one that knows the threshold of what bow wood can take and design concepts for performance. Most will build a bow leaving alot of excess wood and stay very safe with overbuilding. But you seem to love coaxing every once of performance that a bow can give. I'm sure that you've pushed the limits beyond the breaking point more then any can count, but because of that you've learned the limits. Keenan
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"I am going to let mass dictate the tiller and the poundage."
Steve, can you explain how you are going to do this? I usually remove wood to obtain a certain cross sectional shape or profile or arc on the tiller board. Are you just saying that you are going to do this down to the target mass and see what the draw weight ends up at? Jim
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Jim, good question, thats one of the reasons I am doing a build along or possibly several of them is to hopefully see what kind of questions come up. What might seem clear to me might be really confusing to someone else not familair with it.
Ok on this elb I am working on now. I randomly selected a demension of 72" long and 1 1/8 wide at the handle. An elb has certain guidlines it has to meet, The belly need to be rounded starting from the back and it also has to meet a 5/8 rule of thickness, meaning the thickness cannot be less than 5/8 of the width. On this particular bow I simply glued it together, and then this morning I went out and just ground it out on the belt sander to meet the 5/8 rule and got the tiller pretty close with no pre determination on draw weight. ( i will post pics in about an hour) anyway after cleaning the bow up and re weighing it I find the bow weighs 22 oz. A boo backed bow can easily go about 10% less than what the calculator spits out so I go from there. I know now that after final tillering the bow will come in around 20 oz. I simply go back to my calculator and feed some numbers into it to see what poundage, draw length and tiller style would best fit this bow. Elbs have 3 basic designs a sporting tiller, a flight tiller and a war bow tiller. ( elb enthusiasts correct me here if I am wrong) If I use a war bow tiller for instance I would feed numbers in that allow for an arc of the circle tiller. This would be a 0 for stiff handle and fade area and would have a full working handle. The warbow tiller would allow me to build about a 100# bow from this stave and draw it to 30". If I decided on the sporting tiller I would leave the center 8" on the stiff side although they would still have some flex so i would use a 4" figure for stiff handle and fades and this would allow me about an 80# bow for 20 oz. Now if I choose a flight tiller I would keep the center 16" on the stiff side but still flexing so I would use an 8" figure for stiff handle and fades and this would allow me about a 70# bow at 28". Nothing has to be exact here but the formula is giving me a good idea of what I have to work with. I don't have to have any knowledge of this wood as long as I know it is true bow wood to carry out these designs and feel certain of a good performing safe bow. Now it just so happens that I do have some prior experience with this particular specimen of wood and I know it can be pushed safely a little beyond what the formula calls for. So I will actually go for something inbetween the sporting and the flight tiller and look for a finish draw weight of about 80# and a mass weight of 20 oz, possibly 19 oz if I feel lucky. Steve
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Here are a couple of pics, floor tillered and front view, Today i will glue on some overlays which can be removed later for horn nock replacement. Tomorrow hopefully I can tiller it out.
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One thing i want to mention is that I am doing these bows a little faster than I notmaly would and the tillers won't likely be perfect. some guys have a natural eye for tiller and some guys like me can spend a month tillering something and it still won't be perfect anyway LOL. Sometimes it seems like the longer I screw with something the worse I make it. The bow in the pics has about 1/2" reflex glued into it and will hopefully finish out with about 1" of follow or less. Steve
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Maybe a little discussion on the different tiller shapes for elb would be in order right now. I would guess that a sporting tiller is primarily used for lighter weight elbs that one might use for target or weekend clout shooting for instance. Just by the nature of the design of an elb they are allready so narrow that it would be hard to make them narrower for a lighter weight bow. The only real logical way to make them with a lighter draw weight is to just tiller so the outside limbs are moving more and the center of the bow is moving less otherwise there simply wont be enough stored energy to effectively swing that long working limb, if you went narrower they would become lateraly unstable. Using woods with different specific gravities more tailored toward the draw weight and length of the bow you will be shooting can help effectively give you the desired tiller shape, otherwise the mass formula can suggest how to tiller for a specific draw weight based on how much wood you have to work with. Steve
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I went a head and glues some nocks on with super glue so i could keep the buildalong going, here is a pic on the long string one drawn to about 25" and the other with the string hanging down to about 7". The long string will not give an accurate assessment of the tiller but it will give a relatively accurate of where the draw weight is if it were braced. Doesn't seem to matter that the string is loose. If the bow were braced the outer limbs would be bending more than they are now. I am still at 22 oz and the bow is pulling 80# at 25", I am looking for 80# @29" or 30". This is close enough to brace the bow. The outer limbs seem very stable and are not showing any sign of lateral twisting so i will take advantage of this and narrow them a tad more reducing mass a bit further. I can see in the photo that the outer limbs are still stiffer than they should be but I wont attempt to final tiller or tiller much further on the long string. I ned to stop and make a string now. Steve
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Here is a pic of the bow at 25" but at a low brace height, notice how much more the outer and inner limbs are bending with the bow braced. The draw weight is still reading about the same 80# @26". Doesn't seem to matter if the bow is braced or the string is hanging down loose 4" or 6" or 15 " it will read about the same at a particular draw length, but as demonstrated here the tiller cannot be judged unless the bow is actually braced, the higher you brace the bow the more the outer limbs will bend. The tiller on this one will just need a little bit of work and I will need to stretch it out to 30" from 26". I don't have any linen or fastflight string and the b 50 is really a pain to use as it stretches so much I almost get a hernia trying to brace this thing. So far the bow has not shown so much as a whisper of set even when it is first unstrung so I feel confident I have the proper amount of mass in the bow to complete it. It is weighing in at 21 oz right now with 1 oz to go and 4" of draw, right on target if she don't break! Steve
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Something I am kind of tempted to do with this bow. In my chapter comming out in TB4 I have a section on peaking and tweaking. This talks about learning to reecognise when you have a wood specimen that will allow you to push the limits a bit with the reward being a very high performing bow, the risk being a broken bow. One of the main things I am looking at when evaluating a bow for possible peaking out in performance is a lack of set or softening of the bow. If I were to break this bow I wouldn't be out anything as I can't draw 80# anyway. I am considering just fine tuning the tiller on the bow and then proceeding to draw it out further and further and if possible out to about 31" or 32". I would do this 1" at a time with a lot of excersize on the bow at each new 1" increment. After each additional 1" was gained i would unstring the bow and monitor and note the set. Once the bow started to show signs of set i would call it quits or possibly just call that max poundage and start tillering so the weight did not gain as I gained additional inches of draw. This method gets the most out of a bow. I feel like I could easily get 100# out of it as I have allready drawn it to 85#. Not even the slightest sign of set even when measured right after unstringing. What do you guys think? Should we go for broke? Steve
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Pun intended?... maybe just take it to "max." hehe Jim
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He!he! When I say broke i mean broke!!! LOL. Steve
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Might as well live life to the fullest. :) Of course its your wood so as ya see fit.
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Steve,
Interesting to read this thread. Not sure I have my head around the figures side. I look forward to reading TBB4 to see if I can make sense of it.
I weighed the laminated Ipe/Boo bow I am making. 78.5 inches ntn, 1 and 1/16th wide at the handle, 1 and 1/8th deep. nocks 3/8th wide and 9/16ths deep at the nocks. The lims are wider than they are deep mid limb. I am aiming at 110lbs at 30 inches. I am getting a little bit of set mid limb so relfex at the handle is about half an inch. Weight is just about 30 ounces.
I feel I have more wood to come off at the tips and handle. I want the relfex to pull out to stiff at brace and basically full arc at full draw with a slightly stiff handle.
I'd be interested to know what the formula suggests. The bow that broke was conforming quite well to your forumla but bent too much at the handle suggesting that that part was too light and the tips and rest of limb too heavy. for my last bow you suggested 34 ounces and I am four ounces under, though I don't really intend this one to have a stiff centre section like the last one.
Mark in England
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Oh that will make 100#'s easily ;D Just keep those fingers away when it hits 150 on the scale. I'm guessing one of them might still be throbbing a bit..
Bamboo bows just don't explode like selfbows do.. I start enjoying that a bit too much...
You could probably tiller it into a hula hoop if the right wahine was watching :D
Rich-almost friday!
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Ohhh, I hate seeing them break. I say take it to max.
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"It looks longer when sewed back on". Physicians now universally use the term "the Bobbitt effect" for that phenomenon ;)
Pat
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Mark, if you go with a full warbow arc of the circle type tiller between 27 and 30 oz would be good. 29.5 is what it suggests but I always nock off up to 10% more for a backed bow. Something else to think about, the formula will give you a good weight for what you describe but it knows nothing of demensions, do you feel a 78" bow that is 1 1/16 wide will be stable enough when the depth exceeds the width? Probably not the most stable design. In a case like thsi the formula is silently suggesting to change a design or a wood that is being used for a specific job. Often changing the length of the bow or the tiller will bring a bow right into a nice stable design and still well within acceptable mass limits. Steve
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Dang Badger,do you ever sleep.You are either out late or up early like me.Good info and like some others I am still trying to get my thick head around this,I'm going to keep trying.I do already do as you said about between every inch of draw measure the amount of set and when it starts and don't recover in a short time I start looking closer at my tillering methods.It has really helped
as far as set and string follow. :) Thanks for sharing. :)
Pappy
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Pappy, I don't sleep a lot. I work swing shift but still wake up early as if I work days. I usaully take about a 1 hour nap right before I go to work. I have been trying to figure out a better way to explain it where a guy could figure it out roughly without using a pencil and paper. I think figuring out an easier way to express the formula should be my next project. I always like to think of it as starting from zero. A 54" bendy handle bow with a 27" draw would be zero plus draw weight. If the working limb is equal to the draw length ( one one limb) it has zero mass value, if the draw length starts to exceed the working limb we add mass, if it gets shorter than the working limb we remove mass. Setting the tips into reflex adds mass. When we stiffen up the handle and fade area or center of the bow we also shorten the working limb area. So the draw length has a direct relation to the handle and fade area when figuring the mass. When talking about mass on a bow we are talking about 90% of it being in the width of the bow. I will try to figure out an easier way. Steve
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Well, I finished her off at 90#@28" feels real good there and just starting to take a whisper of set. limbs are still straight but lost that 1/2" reflex which come back after setting a few minutes. I think she has flight bow potential, Will sand her down and post her this weekend. wants to torque to the side just a little bit which I dont like but I think I can correct that in the nocks. Steve
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Steve,
I have found that with narrow and slightly unstable bows a bit of careful but brutal sideways floor tillering in the brace shape seem to help. Just push the limbs the way you want them to go, draw, look at the way they are, sidewyas push again and they seem to get the idea after a while. Sometimes they need reminding in the same way but it seems quite effective.
Any idea what you think my bow's mass should be, see earlier post on this thread.
Mark
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Mark, go up about 4 posts, and I commented on the mass of your bow, going to try what you said about pushing the bow sideways abit and trying to train it. Looks like th ebow you are working on should be between 27 and 30 oz but I am a little concerned about how narrow it is, Steve
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MarKinEngland, My last one that length was just over 1 1/4" wide, and usually I like them around 73" for just over an inch otherwise the tapers are just to constant, and sometimes the bamboo amplifies this effect.
Rich
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Thanks enjoy watching you work.Be careful with those didjits(fingers).Learned a few things with this build along.
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New question Steve. I'm building a bendy handle bow that is stiffer in the handle, what do you calculate for the handle. 0" or 2-3" I have dropped my target weight down because it was way to high for the width and physical weight. Justin
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Justin, If it is bendy handle but just slightly stiffer 2 or 3 would be a good number, I always use the word semi because it means 1/2. so if the center 10" is slightly flexing I use half that figure and call it 5". Stiff. This is pretty subjective when it comes to estimating stiff handle area but it will still keep you in the ball park. I have actually built about 12 bows in January, some short some long, r/d, 1 recurve, and a few stave bows. Maybe if the weather is good I will get some photos this weekend and go over the mass on them. I actually use mass on every bow I build. Contrary to popular belief my bows have considerably more mass than they use to have. Whole trick is just making the mass work and keeping it in the right palces. Looking at some of the old primitive relics from different cultures I believe formly that our ancestors had a firm grip on mass placement in their bows. They usually had favortite woods and styles they had become very familiar with so demensions would remain pretty consistent. In our bow building journey we tend to have pet projects that change over time, sometimes they are just evolving and sometimes we change direction all together, currently my pet project is limiting set a bow takes, trying to keep it as near to zero as possible from starting profiles. The type of bows I build are more prone to set simply because I crowd my tillers into short working areas as much as I can get away with. This is why for my mass is so important, I can't get away with underbuilding a bow. I used to rant about overbuilding. I was really pretty hap hazard for many years, a lot of them were underbuilt and a lot of them were overbuilt. I don't expect everybow to be a rocket launcher but I do like to feel confident that when I start a bow I know it will have a high level of performance when I am finished, regardless of the style of bow or wood I am using. ( another rant LOL) Steve
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Thanks, I might need to drop the draw weight a little more or get more bending going on in the middle. I knew I was underbuilt on this one, but when I started seeing set I ran it through the mass and found out just how much. Every bow is a learning experience though. If I push the tiller and andjust the weight I think I can learn to use your mass calculator a little more efficiently. This bow has already proved it works. Justin
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Question regarding reflex, on the form I use to induce a little bit of reflex most of it is
on the outer third of the limb and I usually end up with 1.5" to 2" of reflex measured at the tip
So on your spreadsheet I put that number in correct? With this amount of reflex I'm pretty confident I can
end up with 1" or less of string follow. But that is still up to 3" of set. i guess I'm lost as to how you tiller
to stop this from occuring?
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OK Steve I'm right on track, I forgot the 1/2" of set it took while trying to be to heavy.
Dana, if you keep it down to the weight the formula says the bow can handle, you should be able to keep 1" of reflex. I punched in all the #'s and made sure it allowed me a couple of ounces to shave off during tillering. My bow was way under the target weight so I kept reducing the draw weight on the formula until the mass was where it needed to be. That was my new target weight. Justin
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Dana, if you glue in 2" of reflex you want to keep 1" of reflex. One thing I have found out the last year is how important it is to keep the bow as near to it's original profile as possible. Usually on the type of bow you are describing the oter limbs are pretty stiff, If this is the case add 2' to your draw length on the spread sheet and it will allow for more mass in the working part of the limb. Don't be shy about keeping that inner limb wide, just keep the outer limb narrow. use the mass where the bow is bending most. In my eyes both the elb and the holmgarde are perfect examples of really well designed bows. have you got the current spreadsheet? Steve
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i have the one I posted in a early reply.
i just roughed out a maple stave, the goal is 67"NTN, 55#@27' 4' handle, 1.5" fades so I used 8"
I only have 1.75" width to work with so I kept it that wide for 15" then taper to 1/2" nocks
Once its flow tillered I will put it on form to heat in 1.5"-2" of reflex
your calculator comes in at 21 oz
But I think I should assign it 10" for the handle which changes it to 22.5 oz does this sound about right?
At present its at about 38oz so I have a long way to go
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Jason, that sounds about right, I normaly only use the 8" figure when the bow is pyramid, your tiller will be more elyptical because of the paralell section of the limb. I think your projected mass looks pretty good for that.
I am working on one right now just to see how the formula works on short bows, it was only designed to work down to 54". The one I am doing now is 50" long, stiff handle and fades with 1" reflex, ash backed ipe 35#@ 24". 6' handle and fade section and I deduct 10% for being a backed bow. the formula call for 7.5 oz, I went and checked my glue up and it is about 8.2 oz right now so should be pretty close. I will judge it's success by it's finished profile and it's performance. If it feels stout I may cut it down to 48" and draw down to 23". Steve
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Who's jason ;)
So I keep most of the bend from the fades to where the limb begins to taper to the nocks?
This will result in a elliptical tiller correct. Think I will just call it 23oz and make that my target weight.
Wish I had a little more width but that is all this stave had so I will use it. If I have to I can drop the weight down to 50#
This bow is for a the gentleman that let me cut wood on his property and he's never shot a selfbow so if its
overbuilt some that probably a good thing.
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Dana, once you start getting it bending you will know right away if you have enough width or not. The mass will clue you in real quick. if it is too narrow the bow will be too light when it starts bending. Steve
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Thanks Steve, As was said earlier I think your mass theory has the potential to accelerate the learning curve.
I'm going to apply to the next several bows I make and see where it leads me.
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Ok i've got one limb barely bending when I lean on it and I'm down to 33oz from 38 oz
so I lost 5oz if I lose the same on the other limb that will put me at 28oz, so I will still have 5oz to play with in tillering
and shaping the handle. I actually think I'm getting this ;D
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Do I have to Know this Mass fomula, to be a good Bowyer? Talk about strain the Brain. ???
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No but some of us like #'s and brain teasers. ;D Brain cells are like muscles, use it or lose it. Justin
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Pk, I don't believe anyone ever sugested you have to know the mass thing to be a good bowyer. Plenty of good bowyers have never heard of it. just another method that can be applied by anyone choosing to use it. I am pretty sure know one would mind if you didnt use it. Not mch of a brain strain either, seems like it at first but I use it because it's less brain strain. The turks used it 3,000 years ago, so nothing really new either. Steve
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I never liked math when I was in school(not that I didn't understand it, I just thought it was boring). Now that I have grown up(alledgedly ;D) and have found practical uses for the stuff they were pushing on me when I was younger, It's not so boring anymore. This is definitely one of those practical applications that makes it interesting. And once you get the formula worked out, it's really just simple 'rithmatic. I know I will find this formula very useful. I have yet to make a bow that I have been really satisfied with(I would describe my best efforts as mediocre) and hopefully this will be just the thing to help me achieve satisfaction.
Dale.
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I never took any advanced math in school, not even basic algebra. The formula is derived not from computers but by building bows and making comparisons of weight and set based on performnace. I always take the stats on bows and just kept looking for some patterns to develop, after a few thousand bows patterns do start to show up that even a dummy like me can see. I have never just made one type of bow either, I make all kinds and a wide variety of draw weights up to about 150#, even some I never heard of, I make about equal numbers of stave bows, board bows and glue-ups. As much time as I spend doing it I am looking for ways to make it easier on myself instead of harder beleive me. It.s like the perfect love affair to me, the more I do it the more I want it LOL. Steve
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I've always been impressed with your rational thinking and approach. I look at it kind of like reading music. Some of the best players play by ear but others can learn to read and play sooner than they could by practicing for a lifetime. What I like is the concept of observing and measuring and being intentional about the process. Jim
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I'll play. Badger, I'll sacrifice myself for the interest of science, math and the fine art of selfbowyery. LOL.
Bow #1- 23 oz; made 1/07 from a log stave; 52# at 26 in.; 66 in ntn; 8 inch stiff handled section. Killed a deer 10/07.
Bow #2- 24 oz; 1/2 inch of reflex to start; made 1/08; the rest of the info is the same as bow #1 except for the killed deer part. Lord willing I will make meat with this one too.
Bow #1 and 2 are selfbows. Each is stained and each has multiple coats of spar urethane.
:)
Jawge
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George glad ya joined the party, I ran them thru his spread sheet, now I'm going to wait and
see if what I figured is what Badger figures. To bad wasn't this much fun in high school or college
for that matter.
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Jawge, I made one assumption, correct me if I shouldn't have. I also like about 52# at 26" for myself but I build the bows usually to 55#@28" for a little safety factor. The calculator gives 22 oz, for a stave bow there is usually a little character which 23oz and 24 oz would be plenty close enough. Thats the whole idea, not being exact just being in the ballpark. Most importantly you didn't underbuild them. If the bow were maxed out at 26" and 52# 20 oz would be ideal. Thanks for playing!!! Steve
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Okay, after reading through all the posts, thanks for all the work Badger,i understand the idea. i think i just need some practical application on a bow of my own. this is good stuff. i continue to be amazed at what i learn on this forum, this stuff is priceless.... ;D
Bishop
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George, how about some pictures. The weight and draw length and such are all set #'s. I want to know more about how to determine the length of the stiff handle. I know you get yours bending good in the fades, but Steve also uses stiff tips to adjust that # and I would like to see if he changes the 8" at all so I can better use the formula.
Steve, Ill post some pictures of mine when the finish dries. Justin
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Justin, good questions you asked Jawge, I think you have a grasp on it, I figured his bows more pyramid but I was just thinking that jawge builds his more paralell. This would use about a 12" figure for stiff handle and fade, changing Jawges mass to about 23.5 if I use the 55# 28" draw. I think most of us like to build a couple inches over our draw length in real life. Steve
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When I entered Jawge's numbers it came out at about 21oz, but I'm starting to see
how flexible this calculation is and need to apply a little common sense with it.
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Dana, the handle and fade part of it and learning how to apply that to different styles and tillers is really the whole key. The basic formula for 8" handle and fade would in reality only be used with a pyramid design. One thig we commonly see and I do myself sometimes is to use a paralell limb say to a little over 1/2 the limb but still give it a tiller shape like a pyramid. Obviously won't hurt anything but can contribute to handshock and reduced performance. Gradually increasing the bend throughout the paralell section of thelimb is what the formula is based on. The reason the handle and fade part of it is so important because it correlates into working limb and the mass figure gets generated off of the draw length to working limb ratio. Steve
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So paralel limb say 2/3 rds of limb length then tapering to the nocks = elliptical tiller with a gradual bend
bend from the fade to where the taper starts leaving the last third stiff. And you would assign this design with 10" for
the non bending handle? Assuming a 4" grap and 2" fades.
On another note on my thread "A new Project" I have that elm D bow going. It is essentially floor tillered(a bit stiff) its mass is 27oz
So using your formula I assigned the following values: NTN =60", DL=27" , 4" handle, 2" of reflex and 60#
I looking for 55#@26" with a slightly stiff handle. The formula kicks out 17.5oz. If I play with the draw weight until the mass = what its is presently
it comes out to about 105#, what I'm getting at is you can use this as an aid in not only building a bow but as an aid in designing a bow before you take any wood off. :)
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Badger, the one that is an oz. heavier is twisted. Justin, both bows bend at the end of the fades. I'll post some pics of bow #2 in a sec. Jawge
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Justin, you are correct. On shorter bows I will let the fades and handle bend but I only do that if the stave is short. If you want I can give handle measurements. Bow #2 is 1.25 in. wide at the pass and 1.5 in thick. Both bows are tillered elliptically. Tips are stiff. My style of shooting - quick - demands no stacking. None. Stiff tips contribute to smoothness of draw, as you all now. jawge
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Jawge, where they start to bend is actually not as important as how much paralell limb you have. I use the stiff handle and fade calculation to accomadate that, maybe I should change the name of that particular calculation, it does confuse a lot of people. This part is pretty subjective. I use an 8" handle and fade on my bows and it start to flex right in the fades. I usually make my limbs paralell to mid limb and then smooth out the transition so it tapers up even further, so for my bows usually 10" is the figure I use. If I run the paralell down to within about 13" of the tip then I might use the 12" figure for stiff handle and fade. In the chapter comming out in TB4 it is expalined in more detail. Steve
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Badger that was in reference to Justin's question. Badger, both of these bows are character bows though Bow #2 more so than #1. The amount of parallel limb is dependent upon the tiller for me. Bow #2 has no limb with parallel portions. The idea is this-when tillering a wide limbed bow (bow #2 is 1/5/8 at the widest point), there comes a point when the limb gets too thin for my tastes, a point when the stave does not respond quickly enough to belly removal then I begin to narrow. I learned this lesson the hard way. LOL. Anyway, time for a nap. Gotta get ready for the Pats. I'll post pictures of Bow #2 first. I think it was Justin who asked for them. I don't want to monopolize your thread. Jawge
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Full draw
(http://img.photobucket.com/albums/v331/Jawge/Christmas%20Bow/IMG_1239.jpg)
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Other side. Always a good idea to flip the bow around when checking tiller.
(http://img.photobucket.com/albums/v331/Jawge/Christmas%20Bow/IMG_1236.jpg)
Braced.
(http://img.photobucket.com/albums/v331/Jawge/Christmas%20Bow/IMG_1234.jpg)
Twist, snaky too.
(http://img.photobucket.com/albums/v331/Jawge/Christmas%20Bow/IMG_1233.jpg)
(http://img.photobucket.com/albums/v331/Jawge/Christmas%20Bow/IMG_1232.jpg)
Unbraced.
(http://img.photobucket.com/albums/v331/Jawge/Christmas%20Bow/IMG_1231.jpg)
(http://img.photobucket.com/albums/v331/Jawge/Christmas%20Bow/IMG_1230.jpg)
Jawge
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It worked. Nap time. Go Pats! Jawge
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Jawge, thanks for posting those pics, that helps a lot and makes the explanation easier as well, By the way i like the tiller on that bow, makes for a nice smooth draw. Your bow is bending pretty good right out of the fade in the pic so I would stick with the 8" for handle and fade, the outer limb is relatively stiff but very well tillered so I would use a draw length figure of 30" because of the outer stiffness, This would put you at aboput 21.5 ounces, I would have likely narrowed the outer imbs a bit more to drop the extra 1 1/2 ounces but really not that important still in a good ball park range. Steve
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Thanks, Steve. Can't sleep. Game hasn't started and I'm all wound up. LOL. :) Jawge
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George, thanks for posting the pictures. I didn't mean bendy handle bows, I just hear you reminding people that they haven't got their fades bending on rigid handle bows. Some of us end our fades but do a bad job of getting the first 3" of limb bending, which actually just makes the fades longer. I listen to your advice. ;) I like that style of tiller to with its quick recovery.
Steve, so you add to the draw length for stiff tips, correct. I'm understanding the tillering idea a little better thanks to this discussion. Not just tiller to use with the formula, but tiller as it pertains to the layout of the limb. Justin
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Justin, the reason I add for stiff tips is that the base formula is an arc of the circle, if the tips or outer limbs were bending more or evenly it would be drawing out a couple of inches further, So the stiff outer limbs add some stress to the inner working limb where I would apply the extra mass. On more extreme stiff outer limbs where the last 14 or so inches are almost rigid I figure a 32" draw for an actual 28" draw. As with any method the bowyer will modify it to suit his materials or needs, I find with some materials I figure everthing much more conservatibve and other materials I tend to figure them a bit tighter just because I have a pretty good idea what to expect. Several months ago I had several of our euro bow building brothers give me the length and draw weight only of their better performing war bows, they were really amazed that in most cases the formula was within 1 oz of actual weight. I had to do kind of a crash course in refining it when interest was shown about publishing it. I did find a few ticks in it when applied to different types of bows and with the help and coopertion of several guys on line it seemed to come together really nicely. I do everything by eye and feel when I make bows but when it comes to the mass I really live by it. Steve
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Thanks Steve, I understand. I was trying to add to the handle for the stiff outer limbs because it would reduce the working limb. It makes more sense to add to draw because 3" of handle will weigh more than 6" of limb tip. The parallel limb adjustment is similar to holmegaard design in tiller and mass. More work is done in the inner limb so the limbs must stay wider for a longer distance, and consequently weigh more. You adjust the handle length a little so the formula will allow the extra mass. Justin
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Alright, I just want to make double sure that I am figuring things correctly. I want to make a 54" ntn bend through the handle bow. I want it to draw about 50#@27". The stave has about 1" natural reflex. According to my figures this bow should come in at approximately 11 oz.. If I decide on a somewhat elliptical tiller, I'm figuring about 13oz. Do I have this correct?
Dale.
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Dale that sounds about right, only thing you would add for is the elyptical tiller, and the reflex. 27" is 1/2 of 54" so no add on there. 54" is where it starts so no add on there, 1 oz per 5# draw and about 1/2 oz for the reflex. Steve
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Thanks, now I go to make some shavings :).
Dale.
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I wanted to see how the formula would work on a small kids bow. 51" long, stiff handle and fade, 20#@24". Shoots a 300 grain arrow at 152 and a 211 grain arrow at 167 fps. Calculator projected 7.75 oz bow came in at 8 oz but is not cleaned up yet. I had originaly set the calculation up to start at 54" but it seems to work in reverse as well. Steve
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OK Steve as promised. 69 NTN 3/4" string follow. 65# at 29" I got it bending in the middle so I entered no handle, but maybe your inturpretation of that is different. But hey that is why Im posting it. Justin
[attachment deleted by admin]
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Justin, that came out great, I would use a figure for the handle of maybe 4" maybe 2", but I would be looking for about 20 oz on that bow. How much did it come in at? Steve
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I wondered if you would. I left it a little heavy for figuring 0 but I might still be a little light at 18.5. I figured at 2 it would be 18.5 so I called it good. So now tell me how you get 4 since that was the point of this exercise. Not bending quite as much in the handle and a little stiff in the tips? Asking not telling. ;D Justin
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The handle area is pretty much subjective, Yours is bending pretty good but slightly less than the rest of the bow. From experience we both allready know that ipe is a heavy wood and we also know that there is not much penalty if any for a little extra wood in the middle of the bow. I figured my base weight at about 19 oz for that bow and just gave myself another 1 oz to play with in the center of the bow. Exact figures are not important as long as the bowyer understands where the mass is going and has a good idea why he can distribute it
Your bow is a real good example of sometning else, you did a very good job of keeping the bow stable. At 3/4" wide this is not always easy. I give myself a minimum width of just about 1" for a bow 69" long, I would have left the center stiffer and probably finished the bow around 23 oz but in your case it worked at well just as you did it. I really appreciate you working with me on this. Real life tests are what will make it, break it or change it. Dave Woodbear, will make changes to the calculator as I see it needs. He added a yes or no for backed or unbacked for a 10% deduction. I think I will add a bendy handle choice of slight , moderate, full arc of the circle. This would be close enough. Steve
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Thanks Steve, Justin
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Steve please be sure to post the new excel spreadsheet when its ready, I know I'm learning from this discussion.
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Here is one I am working on right now, I didn't intend to do a build along with it but ran into some problems so thought it might be a good example. As I noramly would I estimated the demensions for this 50#@28" holmie. After roughing the bow out and getting it to floor tiller it became apparent that the wood was not s dense as I had anticapated and I don't have enough mass in the bow to complete the bow as I originaly planned. This is where I play with the numbers and change my design based on the amount of mass available
Original plan. length n to n-66"= 6oz modified- 64"=5oz
nock position +1"= .5oz 0 =0
stiff handle and fade- 10"= 5 oz 8" =4
draw length 30"=1 oz 28"=0
draw weight 50#= 10 50#=10
total 22.5 oz 19 oz
At present the bow is 20 oz, it will likely finish at 18 oz, still a tad light but closer than the original plan. I will tiller the bow to bend closer to the handle to shorten the handle and fade #, I will also get the stiff outer limb bending a little further out to reduce the figure for draw length and lastly I will pike the bow about 2". This is a baord bow and may end up breaking nayway but at the original plan I feel it would have taken too much set if it didn't just break all together, Well back to the workbench.
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Steve, what is the actual draw on that one? I'm sure with the holmie style you must have added some to the draw length to adjust.
BTW I was shooting for a little heavier on my bow, but after weighing and checking I just didn't have enough mass according to your calculator so I adjusted the weight down before I even got to brace. Justin
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Justin, actual draw length is 28", I have it bending more in the upper limb near the fades now and working a bit through the narrow outer limbs. I checked the loisture of ther wood because of all the rain we have been having and it is a tad high at 9.5% so i finished the bow at 47# and will heat treat a bit, mass is sitting at 18.5 oz before rounding off the belly corners and such, shooting a little over 10 grains at 165 but that will go up a bit as it dries out, It took 3/4" set when first unbraced. I put about 50 arrows through it and the weight and the set haent changed so i will proceed to heat treat slightly reflex and then hopefully not expode the bow. Heat treating will get you a lower mass figure as well. This was an edge grained board so I wasn't too worried about cutting the nocks through the back of the bow at the tips. As I finish the bow I will make some adjustments to the tiller also. This is just a quickie belt sander special board bow that I do a lot for my morning entertainment. This one shows a little promise so I will slow down now and try to tweak some good stuff out of it. Steve
For some reasons my pictures didnt work??? Steve
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Badger, I try to get a feel for the density and quality before I start. Also, I look at the rings, etc particularly with osage. Then I decide on a wood width accordingly. What do you do when you are coming in underweight? Looks like you shortened the handle and the bow length which is fine. I guess my question is how did you determine your initial, lay out width? Jawge
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Justin, That bow is bending nice. Dang I'm really starting to like Ipe. That dark wood looks kinda like a stave in my shop. Is it backed/
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Excellent bow, Justin. Jawge
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Jawge, for an initial lay out width I don't want to be too narrow so I tend to make an educated guess on the wider side. This particular bow my educated guess was a bit too narrow. For a mid length bow form a medium dense wood such as maple or red oak I usually start arounf 2" for a stiff handled bow and then narrow it down as I reduce mass. The longer the bow the more I might make it narrow from the start. The formula is actually pretty conservative. A good example, I gave Ibex a yew bow yesterday, I tillered it to 71#@ 29". Steve has a 31" draw and asked if I thought it could handle it. I said lets give it a shot. At 29" the bow onlyhad a hint of set about 1/4" when first unstrung, at 31" draw it took about 1" set, still not bad. The other thing I want to really stress is that being exact is not a critical thing, the mass formula will steer you into a pretty well designed bow if you are pretty close.
Steve
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Thanks, Badger. LOL. Even after all the bows I've made I'll miss weight now and then too. I think his formula could really come into play for me when working with a new wood. Jawge
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Jawge, thats mainly when I see it's usefulness, new style, new wood, new length or draw weight. I especialy like it with the bendy handle and elb bows, Steve
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Steve i have a bow going right now Hard Maple 66" NTN aiming for an actual draw length of 27"@55#
Parallel limbs to mid then tapers to nocks no reflex right now but plan on heating in 1" to 2", 4" handle 1.5" fades
Right now I have it braced at 4" and its pulling 55@14" and its mass is 24.5oz
So I plugged these numbers in:
NTN 66"
Reflex 2"
Handle 10"
Draw 29"
lbs 55#
Comes out to 23.5 oz
Question is it seems like I should have more mass at this point, does this seem to be on course?
this is my first bow using your formula so not sure if using it properly or not. I know a picture would help. :)
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Sounds like you got your profile just about right, you should be pretty close by just scraping the belly now, probably only going to loose about 1 1/2 oz, I was working on one almost identical and I started out too narrow, Mine is down to 18 oz now so i got it working closer to the fades. I cut mine down to 63" nock to nock and am a bit lighter than I want to be but will still go for 50# @27". So far the bow has taken no set and I am at 50# @23". About 1/2 oz wood at the very most will get me to target draw lenght. I wish I had about another 2 oz but am going to chance it. I heat treated the belly. Steve
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Thanks steve, I'm a bit narrow also on this bow if I have to take it 50# I will.
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Dana, The reason you have a low weight now is because you aren't to wide. If you have lots of mass to loose you can tiller the sides of the limb to reduce physical and draw weight. By tillering the belly you loose a lot of draw weight without loosing much physical weight. Remember twice as wide is twice as strong, twice as thick is eight times as strong. Justin
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Steve,
Here is a red oak board bow.
41.7@ 25 (50 @ 28 design, but only drawn to 26)
58ntn, 2.5 max width, 1.2 x 0.75 at handle at center
The back is flat, and the belly is beveled and rounded by 25% in thickness, and 25% in from each side. (cross section factor = 0.065)
What values would you put in to the formula, especially regarding the amount of handle?
(http://farm3.static.flickr.com/2331/2251415284_2f3b8e2251.jpg)
Dave
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I'm at my brace height 6" from inside of grip, she pulling 50# at 20" and mass only dropped to 24oz
so this is actually looking pretty good. I have to get the outer limb bending some more that should take me
out to 24 or 25" then I will put it on the form and add some reflex, Its taken maybe a 0.5" of set that pops right
back so I'm feeling pretty secure at this point
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Dave, this should be interesting as I know you have calculated out the strain and mass ahead of time. because of the elyptical tiller I would allow for a 12" handle even though your actual handle is much smaller. For your bow I would project about 20.5 oz, By the way I liked the add on you did to the calculator for the perry reflex deduction on backed bows.
Dana, I think you are right on target, don't worry about being exact just when you see yourself getting real close slow down and monitor closely the set the bow is taking. Steve
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Havent been here much, nice bows. marlon ;)
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I just have to take the time to say thanks to Steve. On my Ipe selfbow I was shooting for a little heavier bow. It started to take a little set so I ran it through Steve's mass calculator and found I just didn't have the wood to do what I was. I decreased the target weight to 65# that was about where the calculator said it would come out and it didn't take any set from that point on. That was the final 15" of tiller where a bow usually takes set if it is going to. You guys really should try it. Even if it isn't your thing, try it once for fun. Justin
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Thanks Justin, over the last couple of years I have made it a point to weigh every bow I could get my hands on. I was expecting to see a lot of overbuilt bows. I think I saw just as many underbuilt bows as overbuilt. Over the next few years I fully expect to make some refinements here and there. The biggest refinement I would like to make is becomming more wood specific. For example, on yew bows I routinely come in about 10% lower than the formula, same as with most wood backed bows. Osage is another one that can often be safely pushed into lower mass bows. The tension and compression characteristics on some woods is just naturaly better matched on some woods but usually not by a large enough amount to have a significant affect on the formula.
Also, more specific info on how the formula can be applied in everyday bow building. The formula will drive a design on a bow, with some practice we can learn how to use the formula to let us drive the design and use the formula only to help us in our original goal. I am almost convinced that the bowyers of old used this in the elb designs. The old Turkish flight bows were put in classes based on mass weight and not draw weight. I think we are still busy rediscovering old tecniques. Steve
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Ok I have at 55# @25" mass is at 23oz, I lost an ounce but some of it came from
doing some more shaping on the handle, looks like I'm going to be under weight a bit
we shall see, I'm going to add some reflex now so it will be a few days before I can
do any more.
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Dana, I figured 22 if you really get the fades bending. Every day I'm seeing more logic in Georges advice to get more bend in the fades. Justin
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Thanks Justin, I think its going to take a few bows using his calcs to really get the hang of it.
Next one is going to be a bendy handle so we will see.
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The closer you move the bend to the fades the lower the mass you can get away with. Just a little bend near the fades might translate into 3" or 4" of draw length. I always try to leave myself a little room to work near the fades in case I need it when close to final draw weight, very often I do need it. Steve
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I think I have it bending into fades fairly well, I'm going for a more elliptical tiller
with quite stiff outer limbs. I put it on the form today I only ended up with 1" of reflex
my form isn't very agressive. I will give it a few days to rehydrate then finish er up.
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Steve,
Thanks for having a look at the bow.
You are right about having the bow calculated for strain. The bow was calculated for 0.7% strain in the working arms, and slightly less strain in the handle. The center 6 inch of the bow is at 0.6% strain, adjusting to full strain (0.7%) outside of the center 12inches.
The bow mass is 18 Oz. …….I consider the handle as somewhere between full, and semi-working, as the strain is only 15% less than the arms. So, I was thinking that the value to put in to the formula for handle length would be something less than ½ of the 12 inch reduced strain length. However it takes 8 inch (which is more than ½ of 12) to get the actual bow mass. I designed for 28 inch draw to have a bit of safety margin. The bow has 1.5 inch of just unbraced set after use at up to about 26 inch draw. (About 1 inch set rested) It has a crowned belly and is oak so I thought the set to be about right.
Do you think that for a narrowed handle bow, intended to have a working handle, there still needs to be some handle length value put in to the formula, as opposed to, say, a full working ELB style?
Dave
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Dave, I would bet if you had a little more bending in the inner limb it would not have taken that set, I based the projected mass on the tiller you used, it did take a bit of set there so could have used a bit more width in the high bending area ( little more mass) I really like the way you gradualy taper your limbs out of the fades into their high bending areas being the widest, that is a good example of mass logic as it applies to bows. I have one right now I am tillering with the utmost care, so far out to 26" and no sign of set yet, I hope I can make it out to 28" with no set but seldom do with this particular design.
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Trying another experiment just to see how close it comes. Took a 1 1/2X3/4" red oak board 72" long.
I left the center 16" of the bow paralell and tapered the remaining limb to 3/8 tips. After rounding off the corners the stave weighs 21 oz. The center is bending but not as much as the rest of the bow so I am going to give the center a value of 4" for stiff handle and fades. According to this the bow should come out around 65# with no tillering. I am curious how close it will come, if it doesnt break. Going to go cut some nocks and check the draw weight, wish me luck LOL. Steve
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Came out pretty close, bow is drawing 65# @25" and need a little tillering in the outer limbs where it is a bit too stiff. Aftet tillering those out even the bow will be down to about 18.5 oz where the formula says it should draw about 52#. Going to proceed there. Steve
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Well, didn't have to take off as much wood as I thought, bow is at 19 1/4 oz, should be good for about 57#, right now pulling 60# at 26". Taking about 3/4' set, mostly from when I was drawing it to 65#. Not really a great piece of wood and I don't have much time in it so I think I will go ahead and just draw it out to 28" to see if it breaks or takes excessive set. BRB.......
Survived about 1/2 dozen draws to 28" then let go. Was pulling 67# at 28" a bit too heavy for that wood, at 57# it would have been reliable. This was about letting the formula drive the draw weight, seemed to do that pretty well. Steve
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Steve do add a little extra mass for a character stave???
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Dana, on character stves I just play them by ear like anyone would do. If the character is confined to small pin knots I try to keep the mass pretty close, or if the character is a series uf humps and bump without knots I will try to stay close, but yes I do add allow extra but no figures for that I just wing it. Steve
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Steve, Did I miss the finished bow? what happened to the Mulberry one you were going to do at the same time? Looking forward to seeing it.
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i think my head just exploded ;D
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;D ;D ;D I got lost in all the mass jamie. Well , what happened to the Mulberry bow? :-\
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Eddie, I have been running growth rings on it for the last 2 weeks lol. Took a while longer than I thought to get the ring I wanted my shop is outside so the rain slows things down. I should be back on it this week. The wood looks real good , I have two other mulberry staves here that are not nearly as dense. Steve
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Cool Steve, I was looking forward to seeing what you get out of it.