Final Tillering of Flight Bows

My two weights turned up at last, I took them in to the place I used to work and weighed them, they were 10.5 and 10.6 kg. On the way home I stopped at the local post office and checked the 10.5kg weight on their scales, it showed as 10.48kg which was pretty good conformation.
Using those weights to check my scales, showed the digital ones to be accurate and the spring/dial scale to be ok at 45# if zeroed to read 4lb.

I could do the final tillering. The mk3 which is the shortened mk2 was way overweight and despite taking the width down and tapering the riser section down more to give a longer working limb I was struggling to get the draw weight/draw length right. I resolved to use the 26" arrows rather than the 27".
I pulled it to 24" and recorded the weight, pulled to 25" and it went crack , the belly fractured.
It's an interesting failure with a section popping up and out a bit like a geological fault. When I broke off the piece I could see the black central pith of the log dipping from the belly deep into the wood, this was presumably a weak point that contributed to the failure, or at least dictated where it happened. I had assumed that the few pith marks on the belly had been just at the very surface, obviously I would have used better wood if I'd had it to hand.
The main point is that the bamboo back held the bow together. Whereas a failure on the back would result in the bow exploding into shrapnel, this is actually repairable! I could put in a patch or remove about 1/3 of the thickness of the belly and glue on a suitable slat of timber, but that can wait for now.
The bow was very highly stressed and was getting to the point where it was almost as thick as it was wide!

I had better luck with the Boo/Yew/Ipe flight bow (mk4) which is effectively finished now. It's difficult to get accurate poundage readings as when the bow is freshly strung it will read a pound or so heavier than when it's been strung for 15 minutes and exercised.
It's slightly disappointing that the bow had taken a little set, but then it shows it is working hard, and I always say, would you rather have a little set or a smashed bow?

I was anxious about having the bows weighed at the flight shoot, but they explained that they don't take them to full draw, they weight at 1" and 2" less than full draw and use the difference between those as the increase in poundage for the final inch. An example:-
For the mk4:
25"  44.8 lb
26"  47.2 lb              difference between the 2 figures is 2.4lb.
Add the 2.4 lb to the 26" figure to give...calculated figure for 27" of 49.6 lb
Tested it through the chrono' with my test arrow (295 grains)  :-)