Crossbow Limb Delamination

I took the crossbow out on Sunday with my new bright yellow bolts with a view to finding at what range the fixed telescopic sight was sighted. That is to say I wanted to find the range at which the bolts hit where the cross hairs were lined up. Then I could find out how many graticule divisions allowance was needed for each 10 yard step up or down from that range.

Well it didn't go according to plan as when I cocked the bow I heard a slight noise. I took the shot and examined the bow. The foggy looking patch on the back of the left limb looked larger. I was pretty sure the patch was where the glass lamination was parting from the wooden core, this was confirmed when I cocked the bow again and heard more noise and could see a slight gap between glass and wood. I took the shot, which was pleasingly only about an inch from the first, this was V good considering the 30mph crosswind which made it very difficult to hold on target.
Once home I peeled off the glass and for the most part it was pulling wood fibres with it, so the glue was doing it's job. Why the glue line had failed at that one point is probably a combination of things.

I'd taken my usual meticulous care over the preparation and glue up. Maybe I'd clamped too hard, maybe there was contamination of one of the surfaces. Nothing obvious was visible when I examined the surfaces. I've just been into the garage again and before I put on the bench light I could see a slight dark patch on the wood where the delamination started, funny how sometimes poor light can show more than good light, it looked like a slight depression in the face of the limb and, sure enough when I put a rule across the limb and slid it back and forth it showed up a depression in that area which was presumably starved of glue. Not conclusive but certainly something to watch out for in future.

  The epoxy adhesive  EA-40 is a bit of a pain for several reasons, it is expensive and hard to obtain in small quantities, it also has a limited shelf life, it also is best cured in a hot box for maximum strength (but will cure at 20degrees C). This isn't a problem if making laminated glass faced bows is your thing, but for my occasional experiments it's not ideal. So with my usual sense of curiosity I've glued up a test piece from the delaminated glass and a scrap of maple using Cascamite/Resintite (my usual wood laminating glue). I cleaned the parts on the belt sander (coarse grit) and glued 'em up last night and when I looked at it this morning I was surprised to see the glue line showed clear through the glass (bottom pic) despite the glue looking opaque beige when either mixed or cured. (see pic above the lowest one ))
The test piece is currently on a radiator to make sure it's thoroughly cured before I do a destruction test later today....
Just tested it and it peeled apart easily, so that's no good. Mind even the epoxy peels apart with a firm pull, but of course in a bow limb it's not in a peel situation.
I've ordered some epoxy adhesive and some acetone from Easycomposites. It's in a 500g size which is handy and at a reasonable cost. The postage was a bit heavy, but not so bad when I lumped in the 500ml of acetone too. The info said it was good for things like laminating snowboards where some flexibility is needed, so it may be just the job for bows. I'll let you know how it turns out.
They do some interesting carbon fibre tube and rod too, if I wanted to make carbon fibre flight arrows, but for the moment I'll stick to my natural materials.