Stack Thickness vs. Bow Length

[JGR1269]

As a general rule, how much do you guys increase stack thickness when building a 2” longer bow on the same form as a shorter bow? I’m not changing the length of my riser, just increasing limb length.

[jrstegner]

.015 on T/D recurves

[Crooked Stic]

Just longer tip or backing the wedge up ??

[JGR1269]

It’s a one piece hybrid. I’ve been building 54” bows off this form for 6 years. I recently built a 56” bow off this form but was short on weight. I can go as long as 58” on this form but looking for suggestions on how much to bump op my stack.

[bjansen]

I generally get 4-6# more if I shorten 2” and 4-6# less if I lengthen 2”.  So I would calculate the desired lam thickness using the lam stack calculator and your known lam stacks from your historical bows using that differential

[JGR1269]

Thanks for the info.

[Crooked Stic]

5-7 lbs. for two in.

[JGR1269]

I have built several 54” bows that come in around 49-50 pounds with a .310-.311 stack. Anyone care to take a stab at the stack I should go with for a 58” bow at 42-43 pounds?

[bjansen]

JGR, I need to edit my previous comment on 7# for a 2" change - my notes indicate 4-6# instead - sorry about that...thought I had that memorized!

I plugged in your data to the lam stack calculator.  With a .311 stack your 54", 50# bow would produce a 40# bow at 58".  To get a 43# bow at 58" - I think you should use a .319 lam stack.

Mileage will vary of course - you know how it is. If you need a copy of that lam stack calculator, send me your email in a PM - or you maybe able to find an old link on this site.

[JGR1269]

Thanks Brad. I came up with about the same number with the stack calculator as well. I was hoping to get confirmation that It was correct.

[Crooked Stic]

JGR .295.
And its gonna depend on what the weight range of the bow is lighter bows be less than heavier bows

[JGR1269]

Glued up yesterday and roughed in this morning. I went with a .300 stack at the butts, 58”, with 7 5/8” brace and it’s 46#@27”. She’s 1 1/2” at the fade outs and 5/8” at the tips so by the time I take the limbs down to my usual width and work the tips I should be about right.