Primitive Archer
Main Discussion Area => Bows => Topic started by: sleek on September 11, 2017, 04:10:29 pm
-
I am working on very stressed designs and I am to a point where I want to know how tight a radius osage can bend before set starts to take place. Of course what poundage it is also is a factor in that. So there must be a golden ratio between bend radius and draw weight. This will tell me how short a working limb can be at what draw weight and allow me to compensate with deflex of a known angle to get longer draw lengths of shorter bows.
-
I may do tests at 1.5 inches wide to set a standard.
-
Depends on the thickness, a thin shaving can roll up very tight.
Del
-
Draw weight will certainly be a factor. I think I have a billet with no match. It will be sacrificed for testing.
-
draw weight and thickness go hand in hand.
something like this could be used like the tilering gizmo to read the curves
https://www.amazon.com/iGaging-Electronic-Digital-SnapDepth-Fractions/dp/B0063LMXJ6/ref=pd_sbs_328_1?_encoding=UTF8&psc=1&refRID=W089PQK05FMBB13WRPC3
-
Thickness has a lot more to do with radius than draw weight. Ideally any weight bow whether 150# or 20# would be under the same strain. The width of the bow controls the weight of the bow. 2 bows the exact same length could have totally different style bends in the limbs and be different thicknesses.
Sleek the answer to your question is you need to learn how to monitor the condition of your wood as you tiller the bow. ( No set tillering) You can find just the right amount of strain for the piece of wood you are dealing with. Some guys do this by feel and don't even realize they are doing it. However you do it you do need to learn how to monitor the wood. I give some directions on that in the no set tillering thread.
-
Steve, your process is certainly one I need to learn. Its only short coming is that you unfortunately find yourself making the draw weight to the bow rather than the bow to draw weight as most of us would like to do. Perhpas that shortcoming is more mine that your process to be fair.
I am hoping to find a way to get to make the bow the draw weight and length I want and know the dimensions it needs to be rather than work dimensions and see what they will give me. My next bow will be a 50 pounder at 28. Its to be 50 inches when strung. I have a stave just shy of 2" wide and 56" long. How do i get this to give me my desired draw and keep set down while keeping string tension up?
-
How long is a piece of string? ;)
Badger just told you how to do it!
Any given wood has an 'ideal' thickness. Adjust width for draw weight you require.
-
Sorry to say Sleek but I have never found a standard formula for any piece of wood. :)
Pappy
-
You guys are way over-simplifying it by saying 'any wood has an ideal thickness', and it's not true as stated.
-
Steve, your process is certainly one I need to learn. Its only short coming is that you unfortunately find yourself making the draw weight to the bow rather than the bow to draw weight as most of us would like to do. Perhpas that shortcoming is more mine that your process to be fair.
I am hoping to find a way to get to make the bow the draw weight and length I want and know the dimensions it needs to be rather than work dimensions and see what they will give me. My next bow will be a 50 pounder at 28. Its to be 50 inches when strung. I have a stave just shy of 2" wide and 56" long. How do i get this to give me my desired draw and keep set down while keeping string tension up?
Sleek, it is a reality based method. You pull the bow to full target weight every time you pull it. If it won't take it you find out early and lower your draw weight. You can easily build bows to target draw weight without breaking them even if they are way past their elastic limits. They will still be dependable bows yet they won't perform as well. Just the opposite from what you are thinking, it is probably the easiest way to hit your target weight.
-
You guys are way over-simplifying it by saying 'any wood has an ideal thickness', and it's not true as stated.
How else would you say it, every length, weight, design etc will end up at different thicknesses depending on the radius of the bend you are using. I imagine you have a plus or minus factor of a few percentage points either way where it will still work just as well but there will still always be an optimum thickness for any design.
-
Well that's a little better, and kind of what I was getting at, Steve. With your quantifiers and "etc", it leaves THE perfect thickness harder to nail down. Because in reality, and by your own admittance, there are a variety of "perfect thicknesses for any wood".
-
Additionally, the percentage or plus or minus factor you mentioned is much greater in some woods than others...
....not to mention the rather sizable differences of ability possible within a single wood species that could/should cause a bowyer to alter the thickness to width ratio relative to draw weight and other factors.
Just don't want us to paint ourselves into a corner here.
-
I doubt we ever find the perfect thickness unless we just get lucky. I think it boils down to defining to ourselves what is acceptable to us. If you go past the limits of elasticity performance starts falling off gradually at first and then rapidly, if you never reach the limits of elasticity you end up with more mass than you need and it will start to slow you down. You have more tolerance on the too much mass side than you do on the overstress side of the curve. I think the idea is as a bowyer is to refine your skills so you get better at honing in on that ideal area we are looking for. Years ago it was published that about 10% hysteresis is just inherent to wood, we know better now. If you stay within the elastic limits wood has probably closer to 1% hysteresis. If we monitor the wood closely we can keep that number down in the 3% or 4% range. So practically I agree with you that we do have a range, but ideally there are methods that can hone in on that ideal number.
-
I think when someone says "any wood has an ideal thickness," it's not meant to mean any one wood species, but an individual Stave. I think that's what makes steves technique so useful, it doesn't matter what species you start to make a bow with, it allows you to design a bow from the stave you have.
-
Ok High Desert, but that's not an accurate statement either. An individual Yew stave can make an efficient 1" thick English longbow or 1/2 thick flat bow, each with minimal if any set. One twice as thick as the other? I'm not trying to be difficult, I'm just concerned about the message that could be sent to the less experienced and don't want to limit or disuade their experimentation or enjoyment.
-
Ok High Desert, but that's not an accurate statement either. An individual Yew stave can make an efficient 1" thick English longbow or 1/2 thick flat bow, each with minimal if any set. One twice as thick as the other? I'm not trying to be difficult, I'm just concerned about the message that could be sent to the less experienced and don't want to limit or disuade their experimentation or enjoyment.
Sure you can do that but you haven't optimized the design. The whole idea is to give the bowyer one more tool he can use when building bows. Most of the yew elbs I have seen are badly underbuilt and have taken way too much set. They don't need to take any set even after years of shooting.
-
I got a bow from Wayne Olive, a 64" 55# recurve. One of the most well made and performing bows I have ever handled. The bow is 2" wide and weighs 25 oz. Most guys would build this same bow at about 18" oz but I bet they would not perform near as well. He chose dimensions that would handle the strain without breaking down is all it amounted to and it was reflected in exceptional performance.
-
I get what you are saying DWS, but it's still true, the statement just doesn't explain the whole process, it's not an equation. The ELB and the flatbow wouldn't be the same design, so maybe it should read something like "for any piece of wood, at a given design, there is one correct thickness." Design meaning profile, tiller, length etc. that's just my take in it, I'm by no means correct.
-
I get what you are saying DWS, but it's still true, the statement just doesn't explain the whole process, it's not an equation. The ELB and the flatbow wouldn't be the same design, so maybe it should read something like "for any piece of wood, at a given design, there is one correct thickness." Design meaning profile, tiller, length etc. that's just my take in it, I'm by no means correct.
Eric you are correct, the weight of the bow is actually the thing that should have the least influence on thickness. Accomplished bowyers have been monitoring the condition of the wood for a long time, mostly not even doing it consciously so it is not a new thing. I never realized I was doing it until I held a small class and had to explain what I was doing. I had to think about the steps in order to explain it. If we know the wood we are working on and we usually build similar style bows we can hone in on the right design. But if we like to try different designs using different woods and a wide variety of weights it pays to have methods that will guide us instead of building a dozen bows to hone in on something.
-
Steve, Many underbuilt bows from recent years are that way because of your mass theory being a bit too skewed the wrong way. ;)
-
Very possible, I actually find it pretty liberal in most cases but if not applied exactly right I can see where a bow could be underbuilt. You have to allow more mass for every design change that adds stress.
-
You guys make my head hurt! I know you are trying to help, but if I had to guess most new folks would "flip" right through all this and have no clue. I know I don't. :) I just grab a stave and make a bow. I've never weighed a bow and never measure anything after the initial penciled in lay out is done. But I don't make a top performing bow either, well, not that I would know of.
-
Pearl, I am pretty sure you are doing it just naturally and not even realizing it, a lot of guys are.
-
I take the mass principle as a guidine,,
once I see how the wood is responding,,then I follow that,,
watching the wood, and shooting through a chrono tells me alot as I go,,
there are alot of plates to spin,, to get to full draw and good durable performance,,
I learn something here every day, that helps me get there,, thanks guys,, :)
-
I take the mass principle as a guidine,,
once I see how the wood is responding,,then I follow that,,
watching the wood, and shooting through a chrono tells me alot as I go,,
there are alot of plates to spin,, to get to full draw and good durable performance,,
I learn something here every day, that helps me get there,, thanks guys,, :)
+1, except I don't have a chrony. :(
My intuition tells me to first consider the species and quality of the stave I'm using and begin with a roughed out bow that is a bit too wide and bit too thick, but bending.
Then I use Steve's no set tillering as a guide, pulling it to the target draw weight asap and trying to get a nice even bend asap.
From there, I take off an even amount of wood across the limbs (not as easy as it sounds) until I finally reach 1 or 2 inches shy of the target draw length.
After the sanding and such hopefully I'm right where I want to be. :BB
-
I take the mass principle as a guidine,,
once I see how the wood is responding,,then I follow that,,
watching the wood, and shooting through a chrono tells me alot as I go,,
there are alot of plates to spin,, to get to full draw and good durable performance,,
I learn something here every day, that helps me get there,, thanks guys,, :)
+1, except I don't have a chrony. :(
In a nut shell that's the way I do things too.What confirms things for me I'm not stressing the wood too much when tillering towards the end to full draw too is the feel of it when I unbrace it.If it feels very stout yet that's a good thing and I did something right.That might be a wrong or an illusioned observation meaning it's just really dry wood....lol, but it has worked for me.
My intuition tells me to first consider the species and quality of the stave I'm using and begin with a roughed out bow that is a bit too wide and bit too thick, but bending.
Then I use Steve's no set tillering as a guide, pulling it to the target draw weight asap and trying to get a nice even bend asap.
From there, I take off an even amount of wood across the limbs (not as easy as it sounds) until I finally reach 1 or 2 inches shy of the target draw length.
After the sanding and such hopefully I'm right where I want to be. :BB
-
Heck ya Ed. That moment the string slips off and the bow responds says a whole lot for sure.
-
Steve, I hear ya on bow making classes. When I started holding them and having to explain EVERYthing in detail, instead of just doing it, I learned a lot..... more than THEY did, I think :)
-
I am in the doing it by feel crowd. Trying to understand the mass theory and how it applys to the species. I am currently using primarily Osage . I have been moving the mass for awhile now . Steve and Tim have already done this so I am probably just proving what they have already done. :-) oh we'll hardheaded people have to make their on mistakes. :-) I learned a lot about arrows in the flats!
Arvin
-
Arvin
Just wondering if "osage is king" at the flats? Not trying to be a smart ass, as osage is certainly proven to be the best for a lot of things, but have you been considering any others for flight shooting?
-
My intuition tells me to first consider the species and quality of the stave I'm using
Jeff that was a great quote not all wood is created equal and it heavily influences design & mass placement that's something I had to attend some classes of hard knocks to figure it out ,now I let the wood tell me what kind of bow it wants to be rather then forcing my design on the wood !
-
Well Willie Steve still holds the record with a Osage bow so I guess it is. My Osage was 20 yds short but I will blame 15 of that on arrow design. Mine was poor to say the least. But there is next year! And time to build some arrows and bows. I had two blow on me . One the string broke and the other the upper limb. I was shooting flight arrows that weighed less than 200-250 gr. Also I think the bows got too dry . Last day I wrapped best bows with wet towel over night. No problems but shooting 450-500 gr. arrows instead of arrows half the weight. Not sure what the real cause of failure was. Arvin