Beam strength in bending is determined by the strength of the layers
in the outside quarters. Glass will be cheaper stronger and more
durable than the ply. It's heavier too.....

If you use use ammonia, the heat and flat iron won't be necessary.

Brian W

On 29 Dec 2003 19:45:58 -0800, (Kevin) wrote:

My brain must not be fully in gear today.....
the problem with the long list of ply that I found is that it was all
interior grade glue... not exterior as I stated above (guess the
mental clutch is slipping).

So now I think I will either do a layer of 1.5mm gl-2 finnish birch
followed by 6mm of chopped glass and resin, topped by another 1.5mm
birch ply (for 9mm of material) or 4 layers of the birch sandwiched
out with glass & epoxy to the desired 9mm.

Which of the above techniques will be stronger?

The birch is sold in 4'x4' sheets at around $24.00 a sheet plus
shipping (about $10.00). I am trying to also decide which will be more
cost effective as I haven't decided wich is more expensive, an extra
sheet of birch or the epoxy and glass needed to build a 6mm inner
core.

Any thoughts on which technique is more cost effective?

As for bending:

I will soak the birch in a very hot bath, throw in some amonia (into
the hot bath), and spot spray with water & heat it with a flat iron as
needed while applying it (a technique I saw described in one of the
model airplane building groups where the guy said he wrapped 6 inches
1.5mm around a pencil, in a very tight spiral).


Thanks,
Kevin