They often shift a bit especially on high poundage bows. (Mike's are obviously better than mine
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)
When you start to serve the two sides together to close the loop, do some figure of 8 whipping to start the thread , this helps. Also crank up the tension on the string jig and server.
I still get 'em shifting a bit, but you can always re-do the serving that pulls the sides together, or add in a little more... doesn't have to look too pretty.
Couple of days ago I had a guy drop a bow off to me, I'd made it in 2012. He said the string kept coming off
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.
Turns out it was some random old stretchy dacron string, not the one I'd made for the bow. the loops had stretched out like they'd fit a horse bow! I tidied the nocks a bit and re-served the string where the loop closes.
Dunno why he couldn't figure it out himself... I s'pose thats the difference between just 'archers' and bowyers.
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Del