Friday, 28 July 2017

Last Throw of the Dice

Sometimes I'm my own harshest taskmaster and I was beginning to feel I'd had enough of the crossbow project. It's actually performing ok having settled down to about 215fps with the MkI prod, but I'm not really happy with ok.

I realize there are no deadlines, there isn't a spec', there is no boss or customer to satisfy. On the other hand I don't want to plough in vast amounts of time money or effort, so what materials do I have to hand that would beef up the belly? It would be nice to hit 250fps reliably.

Ah, there's the old horsebow which I smashed by overdrawing, I could use the fibreglass laminations off that, that would give them their third outing! What about adhesive? Some of the specialised bow making epoxies are ludicrously expensive but I've got the epoxy resin left from when I made the glass fibre socket for the take down bow. As a rough guide to dimensions (mainly thickness) I have the glass fibre/rockmaple prod which exploded at the start of this project.
So a plan is coming together... Boo back Yew core glass fibre belly, what's not to like?
I've already split/peeled the glass lam's off the belly of the horse bow and started rasping down the belly of one limb of the prod.
Here's a pic of the chrysal and the various prods/bows/lams I'll be working with.
Just out of interest, I reckon that with the two Boo Yew prods being re-worked at different lengths I've gone through about 7 iterations of prod. A lot of work, but you never get anywhere if you are too keen to quit. Of course it helps if you enjoy what you are doing and you've only got yourself to please... mind I'm reliably informed that there is some decorating that needs doing (Yes Dear!)

I'm feeling a bit more cheerful about the performance I've been getting, it's better than the cheaper split limb (centre shot) 90# crossbows and only just slower than the more expensive ones. The bows that are up in the 240 - 300 fps range are much higher draw weights and have 36" prods and longer power strokes.

PS:- For anyone who can't spot the chrysal or doesn't know what they are looking for. It's a silvery hairline fracture travelling up and left from the lower edge of the limb, just above where you can see a pencil lying on the bench.

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