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Backing for Tri-laminate ELB

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Redhawke:
Thanks everyone for helping with this project, it's intimidating to say the least. The plan as of now is to build the bow with Ipe belly, Yellowheart core, Bamboo backing, finished length at 75". I did find plans for an excellent tapering jig from Paul Sellers on YouTube for using hand planes so that concern has been addressed. My next question is how to calculate laminate thickness for the given draw weight and length ? Is there a formula or method that is used ? Also the starting thickness for the core and the taper to thickness.
Thanks again to each of you for sharing your knowledge.

Del the cat:
A couple of things that may help.
1. If you are aiming for 65"... make it 67" to allow a better glue up of the tips and potential for taking an inch off each end to adjust tiller, the poundage or to shift the centre line etc.
2. A linear taper in the core is good, but bear in mind the finished bow isn't a linear taper. The taper increases in the outer 1/3
3. You won't get spot on dimensions for glue up, you'll still need to be tillering, so don't make the belly lam too thin.
I've not done that wood combo, so I can't give figures for thickness... I could make an educated guess if you like!  :) ::)
Del

Redhawke:
Del the cat, that would be extremely appreciated. Yes, after reading several follow alongs on this site I understand the belly should be thicker and thinned during tiller. This is so much different than flat bows.

Del the cat:
I have a 76.5" ntn Hickory backed Yew 80# @ 32" ELB/Warbow.
If you maybe take the thickness figures and use them as thickness of core + belly lam (e.g without the boo).
That should give you plenty of poundage when you add the bamboo back  :)
Upper limb is 37" from arrow pass to top nock.
Distance from arrow pass.  Width (mm) . Thickness(mm)
0 (at arrow pass)                 32.8         27
6"                                       33.2        23.5
12"                                     31.1         21.8
18"                                     30.8         21.4
24"                                     28.4         19.9
30"                                     24.9         17.7
36"                                     19.9         14.4
39" (nock)                           13            11.9

Note:- I mix inches and mm 'cos inches are more suitable for distances along the limb but mm are very convenient for width and thickness.
Hope this makes sense and is of some use.
Del

Redhawke:
Del the cat, it makes perfect sense sir. I want a finished length of 75" so start at 77" and work from that point. I suppose my real question is what thickness should the Yellowheart core lam start at and the end of it be tapered to for finish (or a rough guess)? The Ipe can be added to the equation to meet depth requirements and meet the 100-120 lbs draw weight. I totally agree that mm are easier to work with in many instances. I build cigar box guitars and use mm almost exclusively on those builds.

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