Bamboo backed Trilam Questions

[bluegill]

I have my materials gathered and am planning a core lam of black walnut. Do I need to be concerned with grain orientation (flat, quarter or rift) for the core lam. Also what should I be looking at for thickness/taper for a core of BW?  I am wanting a bow in the low to mid 50's @ 28", Using 66" tip to tip, 11/4" wide? Belly will be Osage.

Thanks Sean

[LittleBen]

Hey Sean!

The old man (Roy from PA) builds a fair number of these and may have some more advice but I'll throw in my two cents.

Better to have a little extra meat on the belly, so I would probably make the core 3/16 tapering to 1/16. Maybe you could go thicker, like 1/4" tapering to 1/8", but obviously you'll end up with a thinner belly slat after tillering.

Search through Roy's threads, he's done at least one buildalong and probably answered this question 100 times.

[Roy from Pa]

For the core lam, the grain orientation doesn't really matter.  1/4 sawn could be a tad stronger, but it doesn't really matter. I make the core lams thickness 5/32nds at riser, tapered to 1/16th at tips. Have no problem getting well into the mid 50 pound range.

[bluegill]

Thanks guys I'll get started on this in the near future.

[mikkekeswick]

The taper on the core is dependant on the bows width taper.
Pyramid will require virtually no taper.
A parallel width limb that tapers only near the tip will require about 0.005 taper rate.
Grain orientation doesn't mater on any of the lams as long as it is straight.