Quote Originally Posted by Derek Cohen View Post
I am sure that the new frame is a good one. Better? I do not know. The old frame is rigid enough. What is more relevant is how you use the saw. Technique trumps extreme tension.
This is particularly true of a fretsaw, where the tension is limited more by the blade attachment than by the frame, which brings us to...

Quote Originally Posted by Jeff Ranck View Post
I have the new one (Mk-IV) and am still trying to figure out if there is something wrong with it. I have to loosen the adjustment knobs as far as they will go and the tension still pulls the blades out of the holder. I've gone back to using my coping saw for now until I can sort out if there is a manufacture flaw or if it is user error (more likely).
Fretsaw blades weren't really designed to be used at high tensions. There's only so far you can go with a simple friction-based retention mechanism like that. If you did somehow manage to tighten the plungers down far enough then the next thing to fail would probably be the blade itself. With that said you should probably make sure there isn't any grease or oil on your blade or plunger ends that could be degrading the coefficient of friction.

If you need that sort of tension then a coping saw is arguably a better tool for the job.