Vallorbe piercing frame

Does any one else have real problems with the new Vallorbe piercing saw frame, getting the bottom nut to secure the blade? I find that when I replace a saw blade putting top nut holds but the bottom nut doesn’t. I have about 6 of these Vallorbe piercing saws in my workshop - as I run classes, and they all seem to do it! 😬 I only have this problem with the Vallorbe piercing saw frame, never with my trusty old eclipse!

Not a commonly found make in UK. It looks as if the saw blade is inserted into a hole and tightened with a knurled nut.

Maybe you can take out the offending nut and see what is preventing the blade from being fully inserted, or the nut from going fully home.

Failing a resolution, I would get a new set of frames with clamps and wing nuts and let your poor students off the hook, so to speak. Dennis.