Primitive Archer
Main Discussion Area => Bows => Topic started by: Bayou Ben on March 23, 2018, 03:59:40 pm
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Badger: "On an R/D bow you have several angles going on at once," Yeah, this is it, too. They are interrelated and at different stages from resting to brace to draw they effect each other.
BayouBen, that doesn't sound like cheating to me, but good planning. Probably took me longer, but I do the same. I thickness taper my belly or cores on a table I made using my power hand planer, then add kind of long reverse wedges to the tips. MY biggest problems came from bows that were WAY stiffer than intended draw weight so that by the time I got it down under ridiculous, I'd messed up somewhere.
Ben, what do you recommend for thickness taper? I never got very scientific about it, but say I take a healthy 70" long x 3/8" lam and I'm adding a 1/8"-3/16" backing and a powerlam. Do you taper it to half the thickness? Or, until it bends evenly to an arc?
I'll leave a foot untapered in the middle (so my fades will come off about where the limb taper starts) and thickness taper from there to just under 1/4" thick at the tips. Then, I may add back 1/8" tip wedges 10" or so long. Can you add anything to improve my method?
I'm reluctant to share how technical I get with taper, because I know so many make excellent bows without measuring much at all. But I guess this style of bow is technical enough with all of the gluing and forms and reflex and deflex, so why not get technical with measurements. I normally use a 0.006"/inch taper rate total. If I'm making a tri lam, I like all 3 lams to be close in thickness, and taper each to 0.002"/inch. That will give you a nice arch tiller then add your tip wedges, powerlam, and reflex/deflex to give you a shape you like. If you rather stiffer outer limbs I would go 0.004-0.005"/inch.
Leaving the 12" untapered in the middle is a good idea it's just hard to do with the way I taper each lam. I use a standard cheap belt sander with a box built around it to grind my lams to spec.
I'm no expert, but like I've mentioned I've experimented with a few different designs. Here's one I glued up last night. It's maple back, walnut core, ipe belly. This is the 1st time I use maple as a backing, so once again I'm experimenting ;D
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Benton I'm glad you posted this, I'm all ready learning I never reliesed those bows had that shallow of tapper rate , Hum! I have a lot of 0.002 lams hanging around in different woods , I like your home made grinder preety creative , I'm following this one paticurly sense your using maple back !
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Ben I've been meaning to try that with my bench sander, got one just like it. How does it work as far as consistency, also did you make a sled for it or a jig?
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I seem to remember encountering some resistance here on this 'primitive' site about trilams and such, so I've not talked about it much, here. It's nice to see it now. I know glass bows are taboo, but if you're as particular about grinding the wood for an all wooden bow, whether a simple two lam backed bow, or a trilam, or whatever... as folks are about grinding glassbow lams, the rest of the build is a lot easier, more straightforward, and better bows result. I've ground lams and cores for all sorts of bows, and I'm set up to do it with variability and accuracy. I too grind tapers from just outside the dips to the tips for most all wooden lam bows. I don't mess around with power lams or tip wedges, I find them unnecessary. Instead, I rely on good design and shaping, good glue joints, and vary the placement and amount of taper, and wood removal, depending on how I want the limbs to act. The extensive groundwork is warranted, and should ultimately be trusted... not fought. In other words, the "let it show you what it wants to be" statement I read in the other thread is something I learned years ago and have been trying to impress on folks who are able to bring the blank to that place, and then comprehend the inherent value in it.
Like I said, it varies depending on other aspects of the design, but for a run of the mill d/r bow, I usually start closer to a .004/1" taper rate, which allows me a little something to work with while tillering.
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Ben, technical is ok! Often you are just putting numbers and method to what other guys are already doing.
Can you describe how your tapering jig works? I think I get it, but want to really understand.
Also, can we share this thread? Should I post the rocking table I use with my power planer to do my tapers? It's super simple, but probably less precise.
If I understand, you might taper a 36" lamination starting 0.375" thick or about 3/8" thick in the middle, 0.006 thinner for each inch of length? Down to about 0.216" on the far end. That sounds about right.
Same taper for a different length bows?
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Next time I do one ill show you guys how I do it by hand. Its time consuming but it works.
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DWS: "I don't mess around with power lams or tip wedges, I find them unnecessary. "
Me neither, I just find them convenient, and sometimes attractive. I've developed a couple of ways to make them quickly and easily, and there is always scrap lying around.
I honestly started using them more to get all the lams I could out of a board than anything else. Finding a perfect tropical hardwood board at McBeath's is rare enough, and considering what they cost, getting one or two more bellies out of it is worth it.
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Benton I'm glad you posted this, I'm all ready learning I never reliesed those bows had that shallow of tapper rate , Hum! I have a lot of 0.002 lams hanging around in different woods , I like your home made grinder preety creative , I'm following this one paticurly sense your using maple back !
So the 0.002" taper rate is multiplied by 3 from the 3 separate lams that are each tapered to 0.002". Therefore the end result is a 0.006" taper. I'm just barely getting into laminate bows but I think that's a pretty aggressive taper not shallow. But if you do have a bunch of 0.002 you can add them together like he did.
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Well the taper rate that Ben posted was 0.006 total stack taper, I would imagine you could use any rate per lam as long as you arrived at 0.006 I was mentioning the shallow taper rate compared to a self bow ! But maybe Ben could comment on that ?
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Set tapers are much more reliable than the eye on these bows. I use a slightly less precision method but I do pre tiller my belly on the belt sander and it gives me a nice shape to start with when I start bending the bow. My eye will always tell me to get it bending more right in the curve and that aint always so.
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Well the taper rate that Ben posted was 0.006 total stack taper, I would imagine you could use any rate per lam as long as you arrived at 0.006
Yeah, the total taper is what matters from my understanding. But I guess different stiffness of materials could throw that off. For example, a 0.006" taper on IPE, in an IPE, Maple, boo trilam, will affect the tiller more than if that 0.006" taper would just on the maple. But generally speaking, most woods are similar in their stiffness relatively so this can be ignored.
I was mentioning the shallow taper rate compared to a self bow ! But maybe Ben could comment on that?
Has anyone measured the taper rate on a self-bow? That would be interesting to know. It would seem that it wouldn't be the same as a laminate mainly because we tend to leave our tips thicker. The only way fiberglass-laminate-makers can really accomplish that is with tip wedges (since you don't really tiller the belly. take too much off and you don't have glass anymore). So if you were to measure a self-bow you would have to measure to the thinnest point before it starts thickening around the tips. Crowned backs and bellies, as well as knots and other irregularities, would also make it difficult to measure an accurate taper rate.
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.006 would be pretty close for a self bow as well without the irregularities. The tips are usually thicker as mentioned. I use thicker tips on my lam bows as well, I don't like them bending at all. I only use a power lam if my belly slat is too thin to start off with.
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That is a hard question to answer depends a lot on working limb and design the tapper rate changes but I just measured 1 of my osage lever bows with a 20 in. working limb 68 in TTT and the average taper rate is 0.012 I'm seeing a average more like 0.010 for my self bows maybe I'm wrong Steve ?
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Parallel limbs will have a more aggressive thickness taper on my self bows.It's hard to judge.When width taper takes over taper thickness wise slows down a little.
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Greg: "But I guess different stiffness of materials could throw that off." It could, and I'm pretty sure variations in bow length and working limb length will affect it too. But, we still have to TILLER wood bows, so the idea is to get close.
"Has anyone measured the taper rate on a self-bow?" THIS is going to vary a lot by style. Pyramid bows, hardly at all. Longbows (which I'm no expert at) I START by roughing out so that the tips are half as thick as whatever the handle is. And that's that's just to see what I really have in the stave and work TOWARD floor tiller, before rounding or faceting anything or narrowing at all.
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Greg: "But I guess different stiffness of materials could throw that off." It could, and I'm pretty sure variations in limb length and working limb length will affect it too. But, we still have to TILLER wood bows, so the idea is to get close.
This is one of the reasons (of many) fiberglass bows don't appeal to me. Sure you can tiller them a little bit by adjusting width or doing minimal sanding on the belly, but they are pretty much set when they come out of the form. Drastic changes in tiller shape just aren't going to happen so you have to have your design right from the start. At least that's my understanding, I could be wrong as I've never tried to tiller a fiberglass bow. Wood, although much easier to break, is much more flexible (as in easier to adjust).
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Yeah, some guys making fiberglass traditional bows, I remember specifically 21st Century Longbows, did use reverse tapers to thicken/stiffen the tips, thereby also moving mass toward the handle, but there is only so much you can do of that in a glass bow.
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Parallel limbs will have a more aggressive thickness taper on my self bows.It's hard to judge.When width taper takes over taper thickness wise slows down a little.
I've wondered about this. How much does width effect tiller? clearly it has a substantial impact. However, I've heard of people saying that their Pyramid Bows are uniform thickness with width being the only variability in tiller, but I can't remember who I heard that from, or if they had actually measured for taper. even a 0.1" inch difference (which is close to a 0.003" taper) may be easy to miss with the naked eye.
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Anyway, here is my lam-tapering method. Don't judge me by my garage, please. :-[
I invented a little rocking table I usually set up on sawhorses. It consists of two 6 foot 2x4's glued and screwed together in the middle, and two 8 foot 2x4's on the outside. The long ones have a large carriage bolt and wing nut on each end so they can be loosened and tightened easily. When loosened, they allow the six-foot doubled up boards in the middle to move freely. When tightned the outside boards hold the inside boards very snug and square.
The outside boards are also braced crosswise at the bottom by two short 2x4s, screwed down with long construction screws. The short crosspieces have a hole in each with a tee-nut installed, and an eye bolt through the tee-nut.
The idea is that I can loosen each end and then adjust the height of the middle of the table on each end turning the eye bolts from underneath. The middle section can be tipped up, down, or flat and adjusted for any thickness of lamination.
Next, I installed wheels on my power hand planer. I wanted 4, but 2 turned out to work just fine. On a full length lam, I can smooth and thickness it after sawing, then tilt one end of the tape up and taper in several passes from middle to tip.
It's pretty handy. It's a little hard to taper two half laminations the same because you have to clamp it on the thick end. I sometimes have start with a few extra inches, drill a hole in the thick end and screw it to the table with a countersunk nylon nut so the planer will ride through without trouble. I can usually just fiddle with the tilt and height enough to clamp the back end of a longer lam with a c- clamp. With this set up, I could even start tapers halfway out the limbs. Sometimes, too, that e ends get roughed up a little because of how the planer tilts without the back wheels, but once the infeed plate at the nose of the planer is firmly up against the work piece, it's fine.
I can put down scrap pieces to protect the table, and produce my wedges and powerlams the same way, planing them down to paper thin at the ends to save time on the beltsander.
Anyway, as I said, not as precise, but very adjustable, and I can easily produce a lam that is 3/8 in the middle, 1/4" at each tip, and 5/16" halfway out as near as my caliper will measure.
Pics are coming. I'm on mobile, so bear with me......
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See the slight incline?
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Top view.
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Underside.
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Tilt. The planer wheels just ride on the two outside boards like rails, planinG the middle.
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That is a hard question to answer depends a lot on working limb and design the tapper rate changes but I just measured 1 of my osage lever bows with a 20 in. working limb 68 in TTT and the average taper rate is 0.012 I'm seeing a average more like 0.010 for my self bows maybe I'm wrong Steve ?
That sounds right, it just depends on the bow and the tiller you are after. Most of mine are what I would call semi pyramid. slight limb taper most of the way down. Parallel would likely come out around 10 but I never measure.
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Steve that makes sense , it took us a couple post to get to the point of what Ed said in 2 sentences...lol !
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Parallel limbs will have a more aggressive thickness taper on my self bows.It's hard to judge.When width taper takes over taper thickness wise slows down a little.
I've wondered about this. How much does width effect tiller? clearly it has a substantial impact. However, I've heard of people saying that their Pyramid Bows are uniform thickness with width being the only variability in tiller, but I can't remember who I heard that from, or if they had actually measured for taper. even a 0.1" inch difference (which is close to a 0.003" taper) may be easy to miss with the naked eye.
Width will affect the poundage more so than the actual bend or tiller.It'll store more energy then.I should say meaning that with parallel limbs using the same type wood.
I don't make true pyramids.Even then the width taper goes to 1/2" wide at tip so a little thickness taper is still needed I would say.Your right though making self bows is more fun especially when you use combinations of width tapering.Parallel from fades to mid limb but slightly a width taper of 1/8" maybe to midlimb nowadays lately on mine then into pyramid towards the tips with very little thickness tapering leaving the tips a little stiffish.
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Greg: "I've wondered about this. How much does width effect tiller? I................."
Now hold on! This IS tiller. This is bow design 101, from the TBB Vol 1. This concept is THE thing you have to know to tiller bows. This is essentially Badger's rule' "thickness determines how much wood CAN bend, width determines how much it WILL bend." This is THE difference between a pyramid, flatbow, and a longbow. Front profile, which is essentially how much width and where) determines tiller shape (how much bend is allowed, and where). We tiller TO the width. Width and thickness are interdependent.
The reason that a pyramid bow (having even side taper) theoretically bends to the arc of a circle is that the thickness is the "exactly" the same. The other reason is that, since the width increases proportionally from tip to handle, the stiffest part is the widest part. The middle is half as stiff as that. Each part of the limb is strained the same amount. Get it? Theoretically, of course. You have fadeouts to work with, and the tips can't actually come to tiny points.
The reason a more parallel sided bow like a longbow has a different tiller is that the thickness varies, and evenly straining each portion of the limb means that some portions are bending more and some less. Guess which portions should be physically bending less?
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See the slight incline?
I have a power planer like that too only a dewalt for laminated bows and bamboo/maple/hickory backings.Nice set up you made.I just use a wide big saw horse with same thickness material on the end of lam or backing so the planer does'nt gouge the last couple inches.
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The wheels solve that on the far end, but can cause it on the starting end. The good thing is being able to start in the middle. Planing without any real jig, or with just a backing for stiffness works great for parallel slats.
As I said, planers save a lot of sanding, too! One of my favorite parts. ;D ;D ;D
If you have any insights on using a planer on bamboo backs, let me know.
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Yep from the fades out with the planer.Usually 3 staggered passes at 1/64" then I see what I got.
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This is the set up I use to grind lams , it's not as creative as you guys but does a great job, but can't do what spring bucks does starting in the middle which is nice for tapering a one peace lam , but to change taper rate is just a mater of changing the sled but even with the fancy equipment it's still hard to get perfect lams !
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Sled
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Greg: "I've wondered about this. How much does width effect tiller? I................."
Now hold on! This IS tiller. This is bow design 101, from the TBB Vol 1. This concept is THE thing you have to know to tiller bows. This is essentially Badger's rule' "thickness determines how much wood CAN bend, width determines how much it WILL bend." This is THE difference between a pyramid, flatbow, and a longbow. Front profile, which is essentially how much width and where) determines tiller shape (how much bend is allowed, and where). We tiller TO the width. Width and thickness are interdependent.
The reason that a pyramid bow (having even side taper) theoretically bends to the arc of a circle is that the thickness is the "exactly" the same. The other reason is that, since the width increases proportionally from tip to handle, the stiffest part is the widest part. The middle is half as stiff as that. Each part of the limb is strained the same amount. Get it? Theoretically, of course. You have fadeouts to work with, and the tips can't actually come to tiny points.
The reason a more parallel sided bow like a longbow has a different tiller is that the thickness varies, and evenly straining each portion of the limb means that some portions are bending more and some less. Guess which portions should be physically bending less?
I know width effects tiller. I understand the principle as you state it but it's good to hear it again. What I meant was, could you only tiller with width. It sounds like you make the argument for this. I should try it sometime. To rephrase this I was wondering is if people ACTIVELY tiller the width like they do the belly. Most of the time I see people shaping the width first then finalize the tiller by adjusting the thickness. Have you ever shaped the thickness first then only tiller the width to get it right? I guess that's what fiberglass bow makers do, it just seems unnatural for me and less effective seeing you would have to remove 8 times the measurement of wood as you would if you tillered the belly. So yes I understood that width effects tiller, that was poor wording on my part. I should have said "how much could you actively tiller with width when making your final adjustments", that is after roughing out the shape of course. My ignorance and in-experience with pyramid or fiberglass bows may be showing. Maybe people actively tiller with width all the time, just not me. That's what's nice about this site. you can learn from other's experiences.
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Good set up too Rich.My friend Grant does his that way too.
All of this tapering etc. just coincides to what portion of the limbs do the most work along the length of the limbs.Highest percentage on the inner limbs but with more wood there to handle it.Less percentage as you go closer to the tips.That's why a nice even ever increasing arch for reflex works so well with it holding a higher percentage farther out to the tips.While taking less set on the inner limbs.These are all Tim Bakers' words I always remember.
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Bytheway Springbuck I like your lam set up. Simple and inexpensive comparatively. I'm guessing you can remove the wheels if need be. I'm in the process of making my first laminate bow, and I had no power tool method of making them or tapering them, so.... I did it the hard way with calipers, a straight edge, and a rasp. Yeah, I don't know if I will do that again let alone how accurate it was. We'll see how it works.
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I don't think things are quite as precise as some seem to think. A Scalloped bow is all over the place regarding width and it still bends as if it has straight sides. The belly would be a series of ripples if you were going to try to follow the width and thickness proportion rules.
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I successfully tillerd one pyramid bow that way. It was red oak blew up on arrow 50 or so. Mostly I end up doing some thickness taper on a pyramid bow. I believe you would have to have the perfect width tape vs length with the right piece of wood to have no thickness tiller.
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Greg: "I've wondered about this. How much does width effect tiller? I................."
Now hold on! This IS tiller. This is bow design 101, from the TBB Vol 1. This concept is THE thing you have to know to tiller bows. This is essentially Badger's rule' "thickness determines how much wood CAN bend, width determines how much it WILL bend." This is THE difference between a pyramid, flatbow, and a longbow. Front profile, which is essentially how much width and where) determines tiller shape (how much bend is allowed, and where). We tiller TO the width. Width and thickness are interdependent.
The reason that a pyramid bow (having even side taper) theoretically bends to the arc of a circle is that the thickness is the "exactly" the same. The other reason is that, since the width increases proportionally from tip to handle, the stiffest part is the widest part. The middle is half as stiff as that. Each part of the limb is strained the same amount. Get it? Theoretically, of course. You have fadeouts to work with, and the tips can't actually come to tiny points.
The reason a more parallel sided bow like a longbow has a different tiller is that the thickness varies, and evenly straining each portion of the limb means that some portions are bending more and some less. Guess which portions should be physically bending less?
I know width effects tiller. I understand the principle as you state it but it's good to hear it again. What I meant was, could you only tiller with width. It sounds like you make the argument for this. I should try it sometime. To rephrase this I was wondering is if people ACTIVELY tiller the width like they do the belly. Most of the time I see people shaping the width first then finalize the tiller by adjusting the thickness. Have you ever shaped the thickness first then only tiller the width to get it right? I guess that's what fiberglass bow makers do, it just seems unnatural for me and less effective seeing you would have to remove 8 times the measurement of wood as you would if you tillered the belly. So yes I understood that width effects tiller, that was poor wording on my part. I should have said "how much could you actively tiller with width when making your final adjustments", that is after roughing out the shape of course. My ignorance and in-experience with pyramid or fiberglass bows may be showing. Maybe people actively tiller with width all the time, just not me. That's what's nice about this site. you can learn from other's experiences.
Combination type tillering belly and width works well on self bows.Even if they are parallel limbs.Especially towards the end of the tillering to your draw weight and length.
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Greg, I hope uyou caught that I was goofin' on ya a little.
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"What I meant was, could you only tiller with width. It sounds like you make the argument for this. I should try it sometime."
Baker mentions this as a common method used by commercial bowmakers "way back then", esp. for laminated wood bows. The issue is that different woods want a different thickness or set results, and methodical thickness tillering can help us discover what that is. More often than not "what I HAVE in the stave", like what the stave will give me determines width and I follow that.
And, yes, the FASTEST bows I ever made was with scouts. Ahead of time, I thinned down the limbs of bamboo flooring boards to @3/8" thick, left the handle 5/8" and added handle blocks. The boys bnacked them with linen and we tillered just from the sides with block planes making pyramid bows.
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Greg; " I did it the hard way with calipers, a straight edge, and a rasp." Good for your arms! I ground out my first set of bamboo backings from Three Rivers, and boofloo lams (cut on a tablesaw) by rubbing them on a 60 grit coarse sanding belt glued to a flat board. I feel ya!
Pat, you are correct of course. A lot of this is theory to be applied as it works later. I do know that having a limb tapering in thickness grow thicker again noticeably causes me issues with tillering, like a hinge right before the thick spot or whatever. Bows I make with a lot of small knots on the limbs end up varying in thickness like that, belly and back both a series of ripples. It's hard to make all the wood work, and these always take some set.
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I made this out of a planer I didn't use. For my sleds I use two pieces of 2"X36"X1/4" plate glass glued together with different sized wire inbetween as spacers to set my taper. I usually use about 5 pieces of wire spaced at the appropriate rate of taper. Makes for a quick and easy and accurate sled.
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One of these days I'll get more serious about making bows and get into more different styles of bows.Nice set up too.
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Sorry I missed all of these comments. I was out of town....Great discussion. That's why I joined this site!
I can't claim my grinder as my own idea, I copied what I saw from another website a couple years ago.
There's a cabinet door hinge on the left side of that ipe board ( a board not good enough for a bow!) that allows it to swing up and down. On the right underside there's a large bolt that adjust the height of board. 1/2 turn does about 0.01". I have a couple bungies holding the board down so it doesn't sway side to side while grinding, and that's about it. It's very simple, and surprisingly very accurate. If I run a parallel lam through it, it will be + or - 0.002", sometimes less if I go slow.
I bought a couple tapered lams that were ground precisely to 0.002". I place my parallel lam on top of the taper and run it through the grinder. The force of the sandpaper rotation holds the lams together, and consecutive passes makes the top match the bottom in taper.
I only have about 0.5" clearance between the board and the sandpaper, so I can't taper an entire board with a taper underneath it, but I really wish I could.
I'll post more pics later in the week.
Very Nice Springbuck. I may "borrow" that idea.
Nice Badger. I bet that's very accurate, I just don't have a spare planer.
Stick Bender, you are cheating! Lol
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To touch on some of the other post, yes the 0.006 taper rate just gets you close for style of bow I build, and different materials, different width profiles, etc will respond differently to that taper rate. The bending beam theory applies more so to these bows since they are generally more uniform and more predictable than lets say a selfbow.
All else being equal, weaker woods will require more taper rate than stronger ones. For example an all ipe bow may require a 0.004" taper to bend in a perfect arch where as an all elm may require 0.01".
On these tri lams approximately 0.003" equals 1 pound difference in draw weight. So if I was planning a bow and I wanted it to be 10 lbs heavier, I would make the initial stack .03" thicker (again all else being equal). It's close enough for taking an educated guess.
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How do you adjust your height Badger?
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Ben I worked every Saturday extra for a sewer contractor sucking out sewer systems to be able to cheat with that...lol it was blood money ! This is a great thread let me throw this out why tri lam I understand the Perry reflex part & glue lines for the form shape , but Marc that makes a lot of lam or backed bows says he has experienced no performance difference between using 2 lams vs 3 lams in a previous thread ? But I have some lams setting in a box collecting dust while I finish the 2 current bows , I was going to try a tri lam Pyramid , core is going to be bamboo,the belly osage , and back hickory , I was going to run the osage belly up the ramps , my core & belly lams are 0.150 with the belly 0.001 taper so I just need to figure out the stack total before grinding the hickory , I need to be close ,not much wiggle room for tiller ! I was going to try to isolate most of the reflex in the outer 1/3 just a exsperment really !
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How do you adjust your height Badger?
I use the height adjustment built into the planer. I also have a long plate that sets on the adjustable side of the sander not seen in the pin. The plate is made from channel iron and inlaid with a 1/2" thick strip of marble for flatness.
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Stick, I'm not sure there is an "advantage" to a tri-lam, it's just another way to do it.
Theoretically it might hold the shape off the form better (I think it does, less "spring-back" as you release clamps, but less "Perry reflex" benefit, as well?), two stage glue-ups give you more time to mess with glue and alignment, and you might be able to utilize a lighter core, etc. but I can't see any real differences.
The only thing I THINK I saw a difference with was when I was using a lot of bamboo flooring. That stuff was developing a reputation for taking set, sometimes lots, but never seemed to really hinge or fret. I started doing two stage glue-ups when I went to TB III, and gluing up belly and core in the form in one stage, then back to the same form for the backing SEEMED to make the bows take less set.
On the other hand, that MIGHT have been about the time I started to have a clue what I was doing.
On that note, has anyone actually tried the method Baker theorizes for laminated bows, where he suggests that gluing up two thin lams in "extreme exaggerated reflex", then gluing each consecutive lam into less and less reflex SHOULD make a laminated bow shoot faster? I never have, because my laminations aren't that thin, and I can get the profiles I want with two or three lams.
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"Blood Money", haha. I may have to get you to make me a couple custom sleds with you blood money grinder; I should watch what I say...And if I'm reading correctly, you already have osage at .15" and bamboo at .15" and you are trying to figure stack for the hickory? In my designs with a dense belly, light core, and bamboo back, I need at least 1/2" total stack to get to 50 lbs. That would put your hickory pretty thick for the back. Of course your design will vary some...
I see now Badger. It's one of those jointer/planer in one units.
Springbuck- why would you think there's less Perry reflex? Unless my understanding of perry reflex is not right, I would think there should be more.
That is an interesting method you mention about less and less reflex. Seems that it would have a spring type effect with coiled up potential energy. I may have to try that out but it will still probably only be with 3 lams. 3 is too much of a headache sometimes, and I couldn't imagine the glue weight on 4 or more lams :o
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Set tapers are much more reliable than the eye on these bows. I use a slightly less precision method but I do pre tiller my belly on the belt sander and it gives me a nice shape to start with when I start bending the bow. My eye will always tell me to get it bending more right in the curve and that aint always so.
Badger I remember you saying that at times you will make at least 1-2 bows a week. I wonder if this "pre-shaping" allows you to be quicker in your bow building. I find that getting from roughed out to brace is the hardest and slowest part for me in bow building. I feel if I had a better expectation of what thickness the bow will be beforehand then roughing it down closer to final shape would speed up that process tremendously. It sounds like you have a good grasp on what it will end up being and can thus predict quite accurately how much you need to take off in pre-shapping before you even get to tillering. I wish I could pick your brain but it's probably something that just comes with experience. In general how thick do you rough your bow down before you begin tillering and do you rough out a taper before you begin with all your wood bows on the belt sander?
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That is a hard question to answer depends a lot on working limb and design the tapper rate changes but I just measured 1 of my osage lever bows with a 20 in. working limb 68 in TTT and the average taper rate is 0.012 I'm seeing a average more like 0.010 for my self bows maybe I'm wrong Steve ?
That sounds right, it just depends on the bow and the tiller you are after. Most of mine are what I would call semi pyramid. slight limb taper most of the way down. Parallel would likely come out around 10 but I never measure.
Parallel limbs will have a more aggressive thickness taper on my self bows.It's hard to judge.When width taper takes over taper thickness wise slows down a little.
So I'm going to try to deduce based off these comments and feel free to critique if you don't think it logically holds up. So a bow needs to taper to bend evenly, or else you would get all the bend right in the middle if it was a flat board, or all the bend will occur right out the fades if it had a handle on it. It seems you can achieve your taper by either tapering width (pure pyramid bow), thickness (parallel limb bow) or a combination of the two. With beam theory, I believe it's stated that removing 1 unit of thickness on the belly is equivalent of removing 8 times that unit from the sides. If Stick Bender is accurate in saying his bows require 0.010"-0.012" taper, then I want to propose a hypothetical. Let's say Stick Bender's bows are parallel limbed as BowEd kind of suggests cause that's a more "aggressive" taper than most people use in the Trad camp. Whether this is true or not doesn't really matter for this thought experiment. If it is true it may be possible to determine the taper you need from either the thickness, width, or both. Supposing a 0.01" thickness taper rate is all the taper you need on a parallel limbed bow, then using beam theory a 0.08" width taper rate is what you'll need for a uniformly thick pyramid. For a 66" bow with 6" handle/fades and 6" stiff tips this would result in 24" working limbs and would require taking off around 0.96" on each side right before the stiff tips. if you still wanted a half inch wide tip you would have to have the limb be 2.4" wide when it starts right out the fade. I'm not sure if this is realistic, it's just what I'm deducing based off of Stick Bender's measurements and Beam Theory (if it can be applied so simply). Subsequently, you could also determine how much width taper you still need if you don't do a 0.01" thickness taper rate or vice versa. For example if you only have a thickness taper rate of 0.004" then you would need a 0.048" width taper rate as well. I calculated that as such (0.01-0.004)x8 = 0.048". Do you think there's any merit in calculating it like this? Sure it's more important to listen to the wood and how it's tiller looks than getting it shaped based on calculations. But maybe it can help when designing the bow and roughing it out to shape.
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Set tapers are much more reliable than the eye on these bows. I use a slightly less precision method but I do pre tiller my belly on the belt sander and it gives me a nice shape to start with when I start bending the bow. My eye will always tell me to get it bending more right in the curve and that aint always so.
Badger I remember you saying that at times you will make at least 1-2 bows a week. I wonder if this "pre-shaping" allows you to be quicker in your bow building. I find that getting from roughed out to brace is the hardest and slowest part for me in bow building. I feel if I had a better expectation of what thickness the bow will be beforehand then roughing it down closer to final shape would speed up that process tremendously. It sounds like you have a good grasp on what it will end up being and can thus predict quite accurately how much you need to take off in pre-shapping before you even get to tillering. I wish I could pick your brain but it's probably something that just comes with experience. In general how thick do you rough your bow down before you begin tillering and do you rough out a taper before you begin with all your wood bows on the belt sander?
I don't use any power tools on self bows, on lam bows I only use the belt sander prior to glue up and then once again to clean it up after I remove the rubber straps.. I never measure thickness. Sometimes I use a thicker backing than others, I don't have a set system. If it is completely rigid coming out of the glue up I might bring it down a bit with the belt sander but that is unusual,
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I do weigh my pieces, if I am projecting a bow to be 19 oz I will want the pieces in the glue up to weigh about 23 0z. I will do some narrowing and thinning as I build.
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gfugal, beam theory is based on the moment of inertia of a rectangular section, where inertia is proportional to the bending strength of the material or composite. So the moment of inertia of a rectangular cross section is the following equation, I = [(Width)x (Thickness)^3]/3. I think there's confusion since people often say double the width and double the strength, but double the thickness and you get 8 times the strength, 2^3=8.
Plug in some of your numbers into that equation and you can see how width and thickness affect strength. It's a cubed root relationship between width and thickness.
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gfugal, beam theory is based on the moment of inertia of a rectangular section, where inertia is proportional to the bending strength of the material or composite. So the moment of inertia of a rectangular cross section is the following equation, I = [(Width)x (Thickness)^3]/3. I think there's confusion since people often say double the width and double the strength, but double the thickness and you get 8 times the strength, 2^3=8.
Plug in some of your numbers into that equation and you can see how width and thickness affect strength. It's a cubed root relationship between width and thickness.
Ah, I see. That statement is only true in that specific example. It's not that changes in thickness always 8 times as strong as changes in width. I'm going to have to do some calculations and try and digest this. Thanks man.
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Yeah, the "twice as thick=eight times as stiff" is not good math. Just a rule of thumb.
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Greg: I feel if I had a better expectation of what thickness the bow will be beforehand then roughing it down closer to final shape would speed up that process tremendously.
Yeah, and with R/D lam bows I definitely had to learn not to start too thick. I was gluing up 5/8" slats with a 1/8" bamboo back at first, which caused things like the bow gaining reflex as I tillered down to a reasonable thickness, and how it took me hours to work down to where I could even get limbs to bend with my whole body weight.
For OTHER than laminated bows, this is what floor tillering is for.
I get the idea of the long single paragraph post, but I can't break it down for you without going over it sentence by sentence. Let me say this, though, that there is merit in doing it basically this way if you care to, have the time, etc. HOWEVER, there are flies in the ointment. As mentioned, bow length and working limb length changes the rate of taper needed. I imagine deflexed portions would, too. Perry reflexing makes the limb MUCH stiffer than gluing on a backing flat and varying the radius of that curve will vary that stiffness as well. Maybe more.
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"why would you think there's less Perry reflex? Unless my understanding of perry reflex is not right, I would think there should be more."
As I understand it, the whole idea behind Perry reflex is that bending the laminations and gluing them COMPRESSES the inner surface of the belly lam and STRETCHES the inner surface of the back. Likewise, it stretches the exposed belly (slightly) and compresses the exposed back slightly. Agreed? Hence, as each tries to relax back or bend, each resists the other doing so at the glue line.
So, as I understand it, there must be some strain in the system created by bending the lams,in order to create Perry reflex in the first place. As with a bow limb, you create more strain by bending a thicker lam than a thin one. If, for instance, you made an entire limb from 1/40" thick veneers (all glued at once) each thin lamination would be too "limp" to create much effect.
I once had a LONG discussion about this with Dan Perry and others on Paleoplanet.net, which culminated with me asking him, "Would it be better to bend one 3/8" belly lam and apply a 1/8" backing, or to Perry reflex two 1/4" lams?" Which would take best advantage of the effect? He wouldn't tell me, so I know it was an important question. He just described how to make models to work with from foam rubber, rubber cement, and marking pens.
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"Would it be better to bend one 3/8" belly lam and apply a 1/8" backing, or to Perry reflex two 1/4" lams?" Which would take best advantage of the effect? He wouldn't tell me, so I know it was an important question.
https://www.tapatalk.com/groups/paleoplanet69529/calling-dan-perry-how-to-tiller-t53163-s20.html#p579487
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Very interesting. I'm going to have to think this through. My initial thought was that a tri-lam offers twice the amount of glue surface for holding the compression and tension forces so it must have more than a single lam, but it is also true that a thick lam holds higher forces than a thinner one.
I now wonder too which one would produce the better result?
In your example I would say a 3/8" belly and 1/8" backing would benefit more since you are holding more force with the 3/8" thick piece.
But in the case of (3) 1/6" lams vs a 3/8" and 1/8" lam, which would you say benefits more?
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Good question and controversial.I'm in the thicker core group with 1 glue line.Most epoxy has a density more so than wood to consider too.Not sure if that's a facter though.
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I don't know what to make of the glue lines in the middle of the bow having a contribution to the performance. My understanding is that most of the work in a bow happens to some degree on the back and more so on the belly surface.
It does seem like there might be some benefit to applying the backing so that it stretches more at full draw.
As far as the belly goes, it seems that if it is prestretched to make the reflexed glue up, it can be drawn as much as it always would have to get to full draw, but if the the prestretched surface is removed, then unstretched or more normal wood is being asked to get drawn further.
If I am using a high elastic modulus backing, (like Bamboo) with a dense, but medium elastic (in compression) wood, like shagbark or shellbark hickery, you would likewise bring the bow closer to finished dimensions to prevent crushing the belly and getting compression fractures.
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I wonder if the tri lam might be more durable in the sense if you develope a crack in one lam it's probably going to stop at the glue line (particularly using smooth on ), of the other ? But that's a good point on the extra mass that Ed mentioned but might be a advantage something like hickory back maple core , osage belly etc ,lightening mass on the core and back . Marc St Louis has made a ton of speedy backed bows and like said ,he said in a another thread he has not seen any performance advantage with more lams ! I guess it is one of those controversy topics but interesting !