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Main Boards => The Bowyer's Bench => Topic started by: BenBow on March 07, 2015, 09:26:00 PM
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I've been shooting a set of sage limbs mounted on a converted darton excel compound riser which made a 62" bow. It just seemed hard to draw plus it's kind of a dog as far as speed goes compared to the homemade longbows I make. So I decided to do a FD curve on the recurve and compare it to the FD curves from my longbow. Now I can see why the comp sage is hard to shoot at my 28.5" draw length and why it's such a dog. The comp sage is a cheap bow to put together but you get what you pay for.
I've only built longbows and you can tell when a longbow will start stacking by when the limb/string angle gets near 90% but that doesn't appear to be the case with recurves. My comp sage recurve isn't even close to 90% at 29" draw but as you can see from the FD curve it starts increasing the lbs per inch from 23" on and really starts stacking after 27". The brace height on the comp sage is 7.25" and 6.75" on the longbow.
Here's a picture of the comp sage and one of my longbow.
(http://i.imgur.com/qePJvKF.jpg?1)
62" Comp Sage recurve FD curve SE/PDF ratio of 81.19%
(http://i.imgur.com/0oVLk6z.jpg)
64" Longbow FD curve SE/PDF ration of 92.66%
(http://i.imgur.com/A9pbx2i.jpg)
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So the question is how do you design a smooth shooting recurve???
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The sage might benefit from more of the outer limbs devoted to recurve and maybe a bit thicker (stiffer) in the inner limbs. Try putting the sage on a tiller tree at 28" draw and measure the string angle carefully.
Even though the longbow is only 2" longer, the working limb lengths are much longer and maybe there is a tip wedge?
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Here's my thought on the stacking issue with my comp sage. As you can see by the pictures if the curve of the non recurved portion of the limb is extended and you calculate the sting angle there it seems to show that a recurve stacks similar to a longbow if you ignore the recurve portion of the limb. You recurve builders have any input to help clarify this?
(http://i.imgur.com/Ozf3asW.jpg)
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Benny Boy, back away from the computer and go work on the wife's honey do list.... You are putting way too much thought into this stuff...
Good wood and good beer is all ya need to make a fast bow.. :)
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From the pictures you posted I can see that the riser of the recurve is way longer. The recurves seem to be static and the bow is shorter than the long bow. The working part of the recurve limbs is probably only half as long as the one of the longbow limbs. Therefore it's no surprise to me that it stacks way earlier.
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Andy
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I tend to agree with Andy- I've got a few questions though- what is the length of the riser, length of the limbs from butt end to the tip and the limb pad angle on the recurve?
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I've converted a few old compounds to recurves and to longbows as well. Some of them I use both ways. I've never run into the stacking problem you describe and I think it's because I'm pretty fussy about the risers I choose for conversion. I don't think your issue is with Samick, I think it's with Darton. That riser is (to me) marginal as a conversion candidate. I look for a bit more deflex than that. Looks like you did a nice job on it though.
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The recurve limbs are Samick Sage limbs and I haven't measured to see what the taper rate is. I had thought about building a 1-piece recurve so learning what the differences are was where I was going with this. After building a few bows I realize I don't save any money doing it myself so I'll save my money and buy one from you guys :)
I had assumed that since the string angle at the tips of a recurve was so much less than a longbow the would be less susceptible to stacking and I see I'm incorrect. They are a whole different animal.
Thanks!
Trux I'll get some measurements for you but the riser is 19" end to end. I'll also get some longer limb bolts and change the limb angle to see what happens. I didn't think there would be this issue since the sage limbs were for a 50# 62" bow but this riser is a reflex riser which doesn't help that's for sure
Roy I'm heading to the garage to get a corona now and I'll try and not ANAL-IZE this any more. :knothead:
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It's the angle at the fingers that determines stack not the tip angle. It's all about the leverage ;)
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Originally posted by mikkekeswick:
It's the angle at the fingers that determines stack not the tip angle. It's all about the leverage ;)
Well, by that logic a long riser longbow would never stack and short bend through handle or horse bows would always stack?
Stacking and what effects it does change between bow types. I think it has much more to do with the string angle relative to the limb's axis than it does to the fingers. But the length and shape of the working limb also have a lot to do with it. I don't think you can simply apply the 90 degree criteria to all bows equally.
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The angle at the string determines finger pinch not stacking. But it is about leverage.
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Ben, I have several classic recurves that I can measure for you. Can't do it till Sunday.
Like a fool, I took a job that's going to keep me busy for a month or so!
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My guess is long riser, long fadeouts = short working limbs. From the pictures it also looks like the taper rate is much higher on the recurve which makes it stack earlier.