Draw length question

[buckeyebowhunter]

I have a customer interested in buying a bow, however he is a big dude and says he believes his draw length is around 31/32". I am not certain how familiar he is with traditional bows, so he may be referring to his draw length with a compound.

I have not built any recurves over 62" inches, and am wondering if I should modify my form to try and make a 64" to accommodate for his long draw. I really don't want to if I don't have to, but I'm not sure if he can get away with a 62" bow. 

Any thoughts are greatly appreciated!

[KenH]

Is the customer local, that he could pull one of your bows (carefully) -- or even just a stick and string -- while you measure to see what his draw really is? 

[buckeyebowhunter]

Ken, yes he is. Good idea

[dbeaver]

I don't know about your form specifically but I just built a 68" bow off my 62/64 form and I got a great profile while strung and a really sweet shootin bow.  Went well for me

[Kirkll]

It would be helpful if you posted a picture of your form. Often times the draw length capacity can be manipulated considerably with taper rates and shifting wedges alone. But lengthening a recurve by going further out on the hook changes the dynamics,  and can result in torsional instability.  This occurs at lower draw weights more often than not, and can be mitigated by backing off on forward taper rate and increasing the thickness at the base of the curl…

BTW…. Limb width profile doesn’t help as much with torsional stability than limb thickness does. You would be amazed how narrow you can actually build a recurve limb with the right geometry and taper rates.

With a one piece form, you can only do so much. But experimenting with going out on the curl further, and using a tip wedge, you could end up with an excellent static tip design that exceeds the performance of your original design…. Nothing ventured…nothing gained.

What taper rate are you using now?

Kirk

[buckeyebowhunter]

Kirk, .002 is what I've always used.

I agree with you on lengthening at the tip end, however I was considering adding length at the butt section in order to keep the curl profile the same. 

I should have mentioned I was building take downs only.

I really don't want to experiment a whole lot, if I had the time it would be a different story. I am hoping I can get him by with a 62" bow.

[Mad Max]

You could make your riser 2" longer

This is a 64" I made years ago. I sold one to halfseminole, he said he was drawing it to over 32" and later told me to 36" and 38", My eyes were squinting when I read the post later. He often said from finger tip to finger tip was 7 foot 



Some info I found years later





He drew thumb ring and liked horn bows too. cool guy


Here is the link to the Original bow he bought if you care to look.
https://www.tradgang.com/tgsmf/index.php?topic=153777.0

[Kirkll]

Kirk, .002 is what I've always used.

I agree with you on lengthening at the tip end, however I was considering adding length at the butt section in order to keep the curl profile the same. 

I should have mentioned I was building take downs only.

I really don't want to experiment a whole lot, if I had the time it would be a different story. I am hoping I can get him by with a 62" bow.

Well i don't know why i was thinking one piece bow, but being a TD it's pretty simple to build a 2" longer riser like Max mentioned.  If you are happy with your .002 FT and have no stability issues going, then stick with it.... but keep in mind .....as you start building lighter draw weight limbs you'll find backing off on FT to .001  or even a par is very effective increasing torsional stability without too much performance loss.  All of my recurve designs performed much better with .001 FT.   Once i get below 35# draw weights on my RC i go with an .001 reverse taper using glass....   Kirk

[Kirkll]

Hey Max.... That is a very cool bow. Lots of work put into that...

[Mad Max]

Hey Max.... That is a very cool bow. Lots of work put into that...

Yes it was a lot of work, I made 4 total

[buckeyebowhunter]

Thanks for the tips gents, Kirk can you weigh in at all on how changing from 002 to 001 FT affected draw weights with comparable stacks?

I have not noticed any torsional instability with my lighter limbs but I have thrown some stabil core in those lighter limbs I have built.

My limbs are essentially just a Bingham with some modifications I've made. Haven't had time to experiment, the Bingham design ain't bad. Very little  hook with their design. So I may just add a inch to each limb and see what happens with some stabil kor. I'm not against making a 21" riser but I really don't know if I want to for just one guy.

[Kirkll]

Thanks for the tips gents, Kirk can you weigh in at all on how changing from 002 to 001 FT affected draw weights with comparable stacks?

I have not noticed any torsional instability with my lighter limbs but I have thrown some stabil core in those lighter limbs I have built.

My limbs are essentially just a Bingham with some modifications I've made. Haven't had time to experiment, the Bingham design ain't bad. Very little  hook with their design. So I may just add a inch to each limb and see what happens with some stabil kor. I'm not against making a 21" riser but I really don't know if I want to for just one guy.

 First of all…. If you are only getting a 60-62” bow out of a 19” riser, I would definitely increase your limb length. You should easily get a 62-64” bow on a 19” riser.

As far as taper rate changes effecting draw weight goes, it’s pretty simple to calculate the addition thickness in the working portion of your limb going from . 002 to .001.  If your working section of the limb is out there at mid limb, and your limbs are 25” in length.  Your limb thickness will be 12.5 thousandths thicker at mid limb.

If your tips are opening up at full draw, and it’s a working recurve design you are building, those .001 tapers are going to stiffen that section up a bit too.   So I think you would be safe dropping your stack height about .016 to hit the same draw weight.

Yup…. That old Bingham RC design doesn’t have a very aggressive hook, an you won’t have as many issues with torsional stability.   But once you start getting your tip notches further out on the hook, is when you start seeing more sensitivity in torsional strength. The use of tip wedges, and making the tips more static will make a big difference in performance, but alignment is critical to keep them from going sideways on you. Once ya start playing with static tips, the thickness at the base of your hook makes a huge difference in stability just using glass and stable core.


These guys building radical static tip RC using .002 FT  successfully obviously have tricks I’m unaware of…. Talk to Max about wild static tip RC’s.  That guys work amazes me…..    Kirk

[buckeyebowhunter]

I think a lot of the old time bowyers with a good amount of hook, like the Assenheimer, used just parallels and glass.

[Mad Max]

I think a lot of the old time bowyers with a good amount of hook, like the Assenheimer, used just parallels and glass.

All my static's but 1 was .004 taper

[buckeyebowhunter]

Did you have a strip of stabil kor in those Max?

[Mad Max]

Did you have a strip of stabil kor in those Max?

Uni-weft glass back then, .030 thick I think

[Kirkll]

I think a lot of the old time bowyers with a good amount of hook, like the Assenheimer, used just parallels and glass.

All my static's but 1 was .004 taper

That amazes me..... I've built a lot of radical recurves in my time, and i just cannot see that much FT in a static tip RC without reverse tapers factored in... How the hell do you even keep a string on them?   Kirk

[Mad Max]

I think a lot of the old time bowyers with a good amount of hook, like the Assenheimer, used just parallels and glass.

All my static's but 1 was .004 taper

That amazes me..... I've built a lot of radical recurves in my time, and i just cannot see that much FT in a static tip RC without reverse tapers factored in... How the hell do you even keep a string on them?   Kirk