Backing for Tri-laminate ELB

[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.

[Del the cat]

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.

Depends on what thicknesses of wood you have available... but...
If it was me I'd make the core a linear taper from about 12mm to 3mm (or maybe 13 - 3) that seems to be manageable dimensions that will still leave plenty of belly wood to tiller.
I reckon on a roughing out taper of between 1.6mm every 6" to 2mm every 6"

Maybe if you taper the core from a little bit thicker (say 14mm) that would allow you to flatten/blend the centre to a flatter, more gentle curve where the two tapers meet, that will make it easier to glue on the belly lam.
Hope that's some help.
Del

[Redhawke]

Del the cat, it helps tremendously. If all goes well I will try to get the lumber ripped into dimension this afternoon. I'm a bit anxious to see how my Freud thin kerf ripping blade fairs on the Ipe and Yellowheart. If all goes well my next step will be to build a tapering jig for the core laminate but that will be a day off project. Thanks so very much Del the cat and all you guys for helping me with this project. I'm unsure if I'm equal to this task and if it were not for such a very special young man I wouldn't even consider trying to build it. I will do my best to add pictures as I go along with the build and I'm sure there will be lots more questions coming from me soon. Many thanks.

[Redhawke]

Del the cat getting close to glue up time for this bow. Do you think I should make a former and add a bit of reflex on this build ? If so how much should I go for and is there a tutorial here for building one ? Thanks again sir, all the help here has been a tremendous help.

[Del the cat]

Personally I wouldn't add reflex to a heavy long draw bow as they are a pig to get to brace anyway, and reflex will make it want to flip on the tiller. If you really want to, then I'd say no more than an inch.
Del

[Redhawke]

That makes sense to me sir and I will not do it. Thanks again.

[Redhawke]

Getting ready for glue up if I can get a nice dry day. Yellowheart core is tapered, bamboo backing flat and thinned. Just got to think about ripping Ipa or leaving it whole. It's a full 1 inch thick. Tried to add photos but made file too large.

[Redhawke]

I will try this again, here are the pictures of the Bamboo that has been thinned and flattened. The Yellowheart core tapered from center to end, and the Ipa belly wood.

[Redhawke]

The Bamboo flattening.

[Redhawke]

Bamboo profile.

[Redhawke]

All 3 lams spread out a bit.