77W!!! Thank you!!! I am buying one of those Bosch units now just so next time this comes up I am prepared!!!
I learned how to use bimetal hole saws back in '82 cutting 5" holes in late 70's Camaros/Firebirds doors through triple steel, spot welds and all! Using a Black and Decker 1/2 hp drill with a big T handle at 700 rpms!  I was taught to lock in using your legs and dont f'n let go.  Dont force it, just let the saw cut as you ease it through...  Slow and steady!!!
I actually snapped off the threaded end of the chuck in the armature shaft after years of use.
You either got hurt or learned real fast how to use hole saws.