Author Topic: underdrawn bows  (Read 693 times)

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Offline DC

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Re: underdrawn bows
« Reply #15 on: May 16, 2019, 08:56:25 am »
This is making me think that I could make a "better" bow by just tillering it/them to my draw length rather than 28". Is there an accurate way to extrapolate the 28" speed from a 27" measurement? Would just a percentage work? Would it be a fair assessment since I'm not actually bending the bow fully?

  DC, suppose you had a bow that was drawing 47.5#@27" and shooting at 186. If you drew the bow to 28" it would be drawing say 50# ( 2.5# gain) suppose your bow is about 75% efficient. That would put you at about 188 with a 500 grain arrow as opposed to 186 with a 475 grain arrow drawing 27". But keep in mind that extra 1" draw will also cause some set in most cases possibly eliminating your speed differential. If this were the case the loss of speed would be reflected when you went back to 27" and shot it again.

So if I was to tiller to, say 24"@40#, then test it. Then tiller to 25@40 and test. then 26 etc. If I notice a drop in increase, stop. At least I would catch it within an inch.
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Offline Badger

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Re: underdrawn bows
« Reply #16 on: May 16, 2019, 09:18:38 am »
This is making me think that I could make a "better" bow by just tillering it/them to my draw length rather than 28". Is there an accurate way to extrapolate the 28" speed from a 27" measurement? Would just a percentage work? Would it be a fair assessment since I'm not actually bending the bow fully?

  DC, suppose you had a bow that was drawing 47.5#@27" and shooting at 186. If you drew the bow to 28" it would be drawing say 50# ( 2.5# gain) suppose your bow is about 75% efficient. That would put you at about 188 with a 500 grain arrow as opposed to 186 with a 475 grain arrow drawing 27". But keep in mind that extra 1" draw will also cause some set in most cases possibly eliminating your speed differential. If this were the case the loss of speed would be reflected when you went back to 27" and shot it again.

So if I was to tiller to, say 24"@40#, then test it. Then tiller to 25@40 and test. then 26 etc. If I notice a drop in increase, stop. At least I would catch it within an inch.

  My original no set tiller method that I still use on flight bows involves shooting as you suggested rather than monitoring the weight. It is much more accurate and sensitive, Super sensitive to even slight drops in efficiency. I just broke one a few minutes ago that was one of my best ever. I am really pissed. 51" long osage recurve. It came off the cawl with 5 1/2" reflex and right after unstringing still maintained 4 1/2" No change after sitting for an hour which is a very good sign. Testing was going great until I got to 24" which was full draw and it let go at a pin knot. I think I can fix it.

Offline MattTheClueless

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Re: underdrawn bows
« Reply #17 on: May 16, 2019, 09:30:58 am »
Way to ruin a guys day, Badger ;)

I'm currently working on a stave the exact same length. Steamed static recurves into it and have tillered it to about the same length.

After reading your post I'm looking at it sitting in the corner and I don't have the stones to draw it past 24"  (--)

Offline Badger

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Re: underdrawn bows
« Reply #18 on: May 16, 2019, 09:45:02 am »
Way to ruin a guys day, Badger ;)

I'm currently working on a stave the exact same length. Steamed static recurves into it and have tillered it to about the same length.

After reading your post I'm looking at it sitting in the corner and I don't have the stones to draw it past 24"  (--)

  Usually on those short bows 24" seems to be about it before they start to show signs of fatigue, I think I could have gotten 2 more inches out of this one if it were not for the pin knot.

Offline MattTheClueless

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Re: underdrawn bows
« Reply #19 on: May 16, 2019, 10:21:04 am »
Yea I'd be happy with 26" of draw. I'm considering a very thin layer of sinew for protection. It's also a setback and static recurve (some call it a 5 curve?) shape, so there's a lot of strain all round. I've got a bit of ostrich sinew lying around, maybe worth a try...

Interesting discussion about under drawing bows, though. It suggests that we all may be losing a huge amount of efficiency simply by the fact that we estimate our dimensions based on the intended draw length and weight. Sure, experience has helped us become reasonably accurate in our estimates, but it really is still guesswork. The closest to a formula we have is your mass principal (which I've read about 100 times, by the way. It's excellent).

Offline willie

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Re: underdrawn bows
« Reply #20 on: May 16, 2019, 03:51:56 pm »
So i am noticing a theme with some longer bendy handle bows is that the bow isnt being drawn to its full length like a 56 inch bow not getting a full 28 inch draw, are there any advantages to a so called šunderdrawnš bow?

from a different angle, not all woods an bend the same "amount" before taking set, all else being equal.
so with a less than superior wood, a longer bow works better