Bamboo backed Trilam Questions

Started by bluegill, December 11, 2017, 08:48:00 PM

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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.

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