lamination advice

[jsweka]

Hi guys,

I've built a few straight limbed longbows using Bingham's kits with good results.  For my next bow project, I want to deviate a bit from Bingham's recipe and also want to try grinding my own lams (It's good to have a father that is really big into woodworking and just bought a drum sander.) This one will also be a straight limbed bow (just love that classic look).

Here's my tentative design specs:
68" nock-to-nock
15" riser
1.25" width at fades
0.5" at string groves

Laminations (from back to belly):
0.050 black glass
0.080 hard maple (parallel)
0.080 hard maple (parallel)
0.080 purple heart (parallel)
0.110 hard maple (0.002 taper)
0.050 black glass

I'm hoping to hit the high 50/low 60 pound range.  Will this get me there?  Any advice on lam thickness or additional tapers would be appreciated.

Thanks,

John

[kennym]

Hi John, That is off the Bingham charts!! 70# is .435 total stack! Check this out...

http://www.binghamprojects.com/Page%2019.pdf

[kennym]

OOps shoulda read closer!! Marty can tell ya what you need,he builds lotsa 1.25 wide bows...

[jsweka]

Kenny - Yep, a little narrower than the Bingham blueprints and kits.  With the last bow I made from one of their kits (cherry and actionboo lams), I narrowed the limbs to 1.25" and cut the riser back from 18" to 15".  I let them know this when I was ordering the laminations and what they sent me was pretty close to what I specified above except that one of the parallels was 0.070 instead of 0.080.  That bow ended up at 54# and I was going for 60#.  Still a nice shooting bow and actually the one that I'm hunting with this year.  So I figured if I just beefed up one of the lams I could probably come closer to 60#, but wanted some additional opinions.  In the other bows I've made where I followed their design, their lamination kits did come within a pound or two of my desired weight.

[kennym]

They are usually real close on the stack. Sounds like you have it nailed. Marty should check in on it,he will know more than me,mine are mostly 1.5 and d/r.

[Apex Predator]

A .450 stack with .004 taper, a 16" riser, and 66" NTN will give me a 55# bow.  Mine come off the form with 1/2" of string follow.  Let's do what I would do.

add two inches nock-nock -      -7#
subtract one inch from riser -  -3.5#
.002 taper vrs .004 -           +2#  ??
Straight profile vrs string follow - +2# ??

If I were building it, I would expect around 48@28 with your recipe.  If it were me, I'd have to go with a stack of around .490.  Results do vary though.  I typically need a thicker stack than most.

[jsweka]

Marty - Thanks for the advice.

This bow is going to be my Christmas present to myself.  I'll post some pics when I get it done.

Another general question - How much variation do you see in finished weights using the same design, but different woods for laminations?

[kennym]

I've found red cedar and walnut to come in about 5# lite on a 50# bow.  That is complete core(red cedar may be even more) I only use red cedar for veneers tho due to strength. YMMV

[jsweka]

Thanks Kenny - I guess this really points to the advice Jack Harrison gives in his book - Take good records on each bow you make.

[kennym]

Exactly right!!