I know on the printer I run now, the hot end manages to pick up a fair amount of charred/misplaced plastic. It cakes up on the hot end over time. Sure, I could get out some sandpaper or the dremel and grind it off, but usually I don't bother with anything but the tip. As a result, I suspect that my hotend would generally fail to make an electrical circuit with a metal bed, even if it were in contact. Also, what's the consequence if you forget to remove the glass when you "auto-level"? Is shattered glass a possibility?
As for finding center: there probably isn't any need to find an exact center. Run the arms up to the limit stops at the top, and name the resulting head position (above) "center". Though it might be difficult to determine when you've reached the top, starting at an arbitrary position, without either a lot of stepper stalling (consequences of this?) or some limit switches.
As for finding center: there probably isn't any need to find an exact center. Run the arms up to the limit stops at the top, and name the resulting head position (above) "center". Though it might be difficult to determine when you've reached the top, starting at an arbitrary position, without either a lot of stepper stalling (consequences of this?) or some limit switches.