Tillering and ash cored trilam ipe trilam ... along the back...

[Tommy D]

So I am trying another trilam - I kerfed some recurve into the ipe tips, then glued some deflex in with a piece of ash - which I think would work very nicely as a backing.

Because of this, I have been tillering the bow in part by scraping down the ash - there is no grain run off. I intend to get the bow bending well and then glue in some "Perry Reflex" with a bamboo backing strip...

A couple of questions...

1) If I am aiming for 70 lbs at 28 inches, any idea what I should aim for before gluing on the bamboo? Overall there is 2" of overall reflex at the moment

2) Could I substitute the bamboo back for an ash back? Any pros or cons?

3) Any advantage to heat treating ash cores or backs?

[DC]

If it helps at all bamboo backing stiffens the Yew up a LOT. I've never measured it but I would guess that my 40# bows are about 10-15# before the boo goes on. I could be wrong because I don't bend them that much but they are very weak before the backing goes on.

[bubbles]

Do you have another 70#@28 to measure for wood thickness? That might give you a jumping off point.

[bownarra]

No when making these sort of lam bows you should write dowen taper rates and lam thicknesses.
Make the bow with your 'best guess' stack.
Once you have the bow made and a draw weight off it. you can adjust stack on the next one to get pretty darn close.
If you cut the core tapered, belly also if you want, you can do away with the majority of weight removal and glue up a bow 5 - 10# heavy then fine tune to where you want it.
Bamboo will stiffen your other two lams like you won't belive! Glue the boo on now then start your tillering.
Ash will work for a backing but unless the grain is perfect your boo would be better.
No point heat treating cores and definately do NOT heat treat the back.

[Tommy D]

Thanks Bownarra - really helpful info as usual there. I really need to make a proper Lam grinder in think.