Limb Design Discussions

[Watsonjay]

Sanity check of my possibly flawed logic.

I am trying to make a short 3 piece longbow that doesn't stack till 30 or as close to as possible.  My current bow is 51" nock to nock. I have about 5 1/2" static tip. It has 001 back taper and parallel belly for cores. It starts stacking around 28-28.5". My thoughts are if I were to use a 002 taper instead of 001 on back lam it would cause the limb to bend more before levering the tips. If I used both parallels it would cause the tips to lever more quickly due to more resistance towards the fades.

Is my logic sound?  I know you guys have a ton of experience out there

Thanks

[Crooked Stic]

If it's one piece your gonna need a short riser. A lot of deflex and a lot of reflex. I have built them with .004 taper per inch. Kinda like a Thunderchild.

[Watsonjay]

Its a 3-piece

[Longcruise]

How about putting a little more recurve out on the limb ends.

[Watsonjay]

Ya I was thinking that would help a little but want to make sure I keep it a longbow strung up I have a little room before it touches the limb.

[Crooked Stic]

I have built longbows 3P with a 12 in, riserdown to 54 in. you end up with not much of a sight window and must cant the bow. I am now building a 50 in. one piece recurve for 28 or less draw. Getting the longer draws out of short bows may be a problem to keep them durable.
Then you have theShrew Tsunami. With wider limbs. Then there is the Hoo-dini that's gotcarbon to keep it stable so who knows. Just depends on how much development you wanna do----

[Watsonjay]

This might be a kirkl question. Im really bummed. I just ram it through the chrono and it only shot 140fps at 9.7gpp and 29" draw. I am wondering if there is too much deflex in my limb pads or ifI need more arc in my limbs. I would like to hit 175fps

[dbeaver]

Theres no recipe.  And no offense to kirk but he is going to ask you about taper rates, stack makeup, pad angle, preload, hook properties, tip wedges and powerlams(which is all informaiton that exists on this forum which has a huge archive of really detailed and great information).  But what does any of that mean to you.  Im not trying to get ruffled feathers or anything but i mean how does changing the various thicknesses and taper rates along the bow limb change how the bow acts to you as a bowyer? Is it just factors or can you see how they physically influence the dynamic bow bending?


Kirk when you see this, i appreciate you dont get me wrong.

There's a ton of information out there on what taper rates do as a function of limb bending and how and what the influence of changing that parameter will do.

[dbeaver]

Sanity check of my possibly flawed logic.

I have about 5 1/2" static tip. It has 001 back taper and parallel belly for cores. It starts stacking around 28-28.5". My thoughts are if I were to use a 002 taper instead of 001 on back lam it would cause the limb to bend more before levering the tips. If I used both parallels it would cause the tips

So to help in some way after my rant.  001 back taper and parallel belly, total taper rate still 001 parallel doesnt matter.  assuming thick side of taper is to bow center;  If you want the entire limb to bend before the hooks start to lever you would remove the taper at all and have paralell laminations.  This would make the lamination coming off the wedge the same thickness allowing the limb to more evenly distribute the bend amongst the whole limb. This would move the hook the furthest distance and would take the most energy to return to brace.  If you increased the taper rate from .001 to .002-.004 then the difference in thickness from bow center to the hooks is even more dramatic, meaning that the part of the limb coming off the fade or wedge will be substantially thicker than at the tip.  This limb will bend closer to the hook and resist bending near the wedge/fade/handle where due to the total taper rate is thicker ratio from center to tip than.

For getting your  fps up the taper rates will help where the energy gets stored and what parts of the bow use up the energy while returning to brace, so adjusting for taper rates may not help you as much as a different design that incorporates preload.

Stacking has to do with the string angle reaching 90 degrees and the pull characteristics change.  Having your limb bend further out and will change the point of rotation for for that string angle. also some good archived threads about stacking.

I have way less functional experience than the "authority" of my claims but im here to understand bows and this is what i think ive learned.  Id love some discussion.

[Watsonjay]

Sanity check of my possibly flawed logic.

I have about 5 1/2" static tip. It has 001 back taper and parallel belly for cores. It starts stacking around 28-28.5". My thoughts are if I were to use a 002 taper instead of 001 on back lam it would cause the limb to bend more before levering the tips. If I used both parallels it would cause the tips

So to help in some way after my rant.  001 back taper and parallel belly, total taper rate still 001 parallel doesnt matter.  assuming thick side of taper is to bow center;  If you want the entire limb to bend before the hooks start to lever you would remove the taper at all and have paralell laminations.  This would make the lamination coming off the wedge the same thickness allowing the limb to more evenly distribute the bend amongst the whole limb. This would move the hook the furthest distance and would take the most energy to return to brace.  If you increased the taper rate from .001 to .002-.004 then the difference in thickness from bow center to the hooks is even more dramatic, meaning that the part of the limb coming off the fade or wedge will be substantially thicker than at the tip.  This limb will bend closer to the hook and resist bending near the wedge/fade/handle where due to the total taper rate is thicker ratio from center to tip than.

For getting your  fps up the taper rates will help where the energy gets stored and what parts of the bow use up the energy while returning to brace, so adjusting for taper rates may not help you as much as a different design that incorporates preload.

Stacking has to do with the string angle reaching 90 degrees and the pull characteristics change.  Having your limb bend further out and will change the point of rotation for for that string angle. also some good archived threads about stacking.

I have way less functional experience than the "authority" of my claims but im here to understand bows and this is what i think ive learned.  Id love some discussion.

thank you, that helps a lot. Basically my logic was backwards.

My logic also says if I decrease my pad angle it will add more preload and speed??

[dbeaver]

It may, but thats where the fun comes in.   Anyone wanna share one of their adjustable risers for watsonjay?  Aluminum body adjustable pad angles and sometimes can be adjusted a few inches between say 16-20 inches(or whatever) depending how you construct

https://www.tradgang.com/tgsmf/index.php?topic=185947.0

[Watsonjay]

It may, but thats where the fun comes in.  Anyone wanna share one of their adjustable risers for watsonjay?  Aluminum body adjustable pad angles and sometimes can be adjusted a few inches between say 16-20 inches(or whatever) depending how you construct

https://www.tradgang.com/tgsmf/index.php?topic=185947.0

Ya, I am going to have make one of those.

[Watsonjay]

I measured my limb pad angle and I am at 17deg. I think I will bump it down to 14deg and use parallels for the core to see what happens

[Kirkll]

It's a long process tinkering with different limb shapes, and adjusting limb pad angles to maximize preload. Along with shifting wedges and positioning working limb, and adjusting the length of the working limb.

But there is one more factor that really makes a difference in your performance that should be notet, and that is the limb travel... higher pre load , with a shorter limb travel makes a huge difference in performance ....  I didn't quit tinkering until I was hitting high 190's at 10 gpp myself and over 200 fps at 9 gpp.

I was using .004 FT on my hybrid LB at first, but got better performance at .003 FT.


The most important thing to remember is that you need to dial in your pre load and limb shape at brace with your adjustable riser. Then mount it on your riser block before shaping the grip and measure back from the string to locate the deepest part of the grip.

[Watsonjay]

Does anyone sell these adjustable limb pads riser? It would be nice to have an aluminum one like kirkl's

[OldRawhide42]

I made one from a old compound . Just cut off some of its limb and bolt yours on it. Use the compound weight adjustment bolt to change the angle.

[Watsonjay]

I made one from a old compound . Just cut off some of its limb and bolt yours on it. Use the compound weight adjustment bolt to change the angle.

Any pics of this? Hard to imagine.

[OldRawhide42]

Old compoumd

[OldRawhide42]

As of right now it goes 17° to 22°

[Watsonjay]

As of right now it goes 17° to 22°

Pretty slick. Just an old compound. Usually they have really long risers. How do you adjust for riser length?