Pete; most of the saw plate I use for making backsaws is still coiled. After shearing to length, the next thing I do is lightly joint all 4 sides side with a flat file. 9/10 cases it removes the stored memory of being coiled. The odd case is generally rectified after being toothed and fitted to its hardback. I shape all my saw teeth by file, and by deepening each of the tooth gullets in progressive passes, the saw plates flatness is not compromised. That's should not suggest I am trying to undermine the use of a Foley Machine.
Stewie;