Thursday, 15 March 2018

Close But No Cigar

I'd had a good day helping my mate JT work on the Hazel longbow, the belly patch was worked down to blend in to the bow, but left a whisker plump, the horn nocks were roughed out enough to fit the string at a low brace and flex it, pulling it to 45# at about 22". It looked much better and the right limb which had chrysalled and gone weak now looked a hint stiff with the tiller restored to a reasonable shape. We quit there as we'd had a good session and didn't want to spoil the work by rushing.

By teatime I couldn't resist testing the crossbow and it worked nicely  201.1fps first shot, but then 200.5fps on the second and it then went on to loose about 2 fps of speed with each shot!
After 7 shots it was down to 188.8fps, I was just pushing it too hard, I'd taken a few turns out of the string to lower the brace height a whisker and take some strain off it to no avail.

Bang! The string cut deep into the nock on the left limb splitting down along the lower edge, this made the string slack and allowed the limbs to flex past their unbraced position splitting the belly lams away from the core.

If only I'd double served the loops or bound below the nock with linen thread soaked in superglue. Easy to be wise after the event, but even if I'd done those things, it may well have lost speed.
I've proved some aspects of the design, the bow mount, the Boo/Yew /Ipe combination, the 120# draw weight. The nock failure was at least different to the last one which virtually snapped off.
Am I down? Of course I'm not (well just a tad) I could buy a crossbow, but what would I learn from that. I'm hedging my bets, I've seen some nice maple slats on E-bay which I've ordered, these can be used with Boo/Ipe, or maybe I'll succumb to the lure of glassfibre laminations.
I'll probably have another go with the natural materials but with an extra inch on each limb, and better nock design. The belly lams will go right into the mounting/riser block this time so they won't simply split off if the bow flexes beyond it's rest position.

No comments:

Post a Comment