A good motto to observe throughout life is, never play pranks upon medics. But play a trick on them when you're meant to be at death's door: just keep on living. They won't know how to take it. It's a fantastic wind-up
Thanks for the info. But I did mention that it is a circular saw; not a bands saw.
Even if it comes loose, it just loses grip and simply stops in the cut. The motor keeps on turning.
It can't come off due to the design.
My first job after leaving school was in a timber yard. We had big circular saws driven by tractor power take offs. Also some large band saws for ripping trunks. Quite hairy when the blade comes of one of these.
Anyway, I have tightened everything up, and will monitor the situation.