Thursday, 19 November 2015

More Work on the Yew Longbow

I've tidied up the limbs a bit and cleaned up the edges on the belt sander to remove the last of the bandsaw marks and to narrow the tips a tad.
I've done a fair bit of work on the undulating tip and done a video of that work.
I'll soon be ready to increase the brace height and get it back on the tiller, I've taken thickness measurements every 6" on the upper limb, this will help me even it out. Generally I look for about 2mm of taper every 6".
Here are the measurements:-
Thickness at centre 30.2mm
6" from centre 27.6
12"                  24.6
18"                  24.1
24"                  21.3
30"                  19.5
36"                  16.9
Now you can see, that's not very even and if I take even 2mm steps from 30.2 down wards, I wont get down to 16.9mm.
So I probably need to thin the grip a bit. But lets assume it's about right at the 6" mark and the tip ( We can leave the grip a tad thick) and lets see what would be an even taper. 27.6-16.9 is 10.7 and this would be divided into 5 equal steps.
So 10.7 divided by 5 is 2.1 (to one decimal place)
If we work out the thickness reducing by that step we'd get:-
6" from centre 27.6
12"                  25.5
18"                  23.4
24"                  21.3
30"                  19.2
36"                  16.9
If we look at those figure we can see that we ate a tad thin at 12" and a bit thick at 18", the rest are pretty good. No need to worry about the 12" figure being a bit this as the whole limb is still probably too thick. Basically I can just thin the limb at the 18" point and blend it in before it goes on the tiller.
It's not exact, as the taper on the finished bow won't be dead even, it will get thinner than that at the tip, it's just a check to keep things on track. We don't make a bow by numbers... the measurements are for guidance, not to be our master.

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