I like to make Hill Style Bows. I put about 1 1/2" of backset in the limbs. The mystery started when I noticed that the current bow I am shooting has lost about 10 fps in arrow speed (But no loss in draw weight of 55lbs). While investigating I found that it had lost about 1/2 inch of backset.
I have made 4 bows on this form. They all have .050 glass front and back. They all have many 1000's of shots through them. 3 of them have red cedar cores, 1 has a bamboo core. They are identical in all other respects. One of the cedar cored bows and the bamboo core bow both show a loss of backset (same loss of 1/2 inch), while the other two bows don't.
The only thing I know I did differently during construction is that for the 2 bows that developed backset, I left their lams in the oven at 100 deg overnight to dry out. I am haphazard about drying the lams. Sometimes I do, sometimes I don't. And I didn't record this step in my notes, so I am not 100% confident about it. I am 100% confident that I dried the bamboo lams, just not 100% confident about which cedar bow I dried the lams for.
The loss of backset seems to be evenly distributed though the outer 2/3's of the limbs. Although this may be an optical delusion.
Any Idea's? Here's what I can deduce from the facts:
-I know there must be an answer as 2 of the bows did not take set.
-It can't be a material issue as both a cedar and a bamboo took set, Yet 2 cedar bows did not.
I thought drying lams would improve performance. But I am wondering if that is what led to the backset issue. I have a theory about it, but it's weak so I won't bother sharing it.
I didn't think Glass Bows could take set. Silly me I guess. All suggestions are appreciated!