Core Lam Grain Orientation and Thickness

[arachnid]

Hi guys.

Just a little question:
When making a tri-lam, does the core have to have straight grain like the back or not?
And, what thickness should the core be (if, lets say, the belly is ipe).

Thanks
 Dor

[mikekeswick]

It doesn't have to be perfect but it helps! People will say that it doesn't matter but i've had cores pull apart (padauk) and the back and belly have been fine.
If you are playing about with new designs just use maple - it is the PERFECT core wood for a whole heap of reasons. Once you've got your design where you want it then start to experiment. Generally diffuse porous woods are best.
Start with thin cores, then try tapered cores...then you'll know! Main rule is thin enough (or tappered enough) that you don't run out of belly wood.

[arachnid]

Well I got my hand on a board of african walnut. Might not be as good as maple but I think I'll use it for a tri-lam: ipe belly, african walnut core and white oak back.

I'd like to know if you have any suggestions for the bow dimensions.

Thanks.
Dor

[Springbuck]

  It needs to be basically straight.  In my experience.  If the grain runs off the belly sharply front to baclk or off the side, it can lift.  It's a funny fracture, more like a spall (spalt?) than a fret.  The grain slips, and on the belly a lip of grain that hangs out will form.  In a core, a hinge will form, and sometimes you can see a tiny separation in the lams.

Backs need to be perfect. bellies darn good, and cores ok.  General grain should run mostly the length.

[bow101]

The grain should be reasonably straight. Just use 2 pieces from the same cut and oppose them.  And watch out for grain run off, and pay attention to the edge grain that it is straight.

I would use domestic woods, like Maple, White Oak, Hickory, Osage,  Yew, Ash,  Cherry, Elm.  Most domestics are not as expensive and you do not have to deal with the oils in the wood.  Besides why not support your local wood cutters and growers. ..........