canadianavenger wrote:And if software becomes out of sync with reality because of lost steps, you can crash your head, whereas the endstop will help prevent this by "advertising" the lower limit.
That's the canned answer i always hear when i mention top endstops.
Unfortunately, it has very little basis in reality.
If you're skipping steps, you've got more problems than a "crashed head". Also, a lost step or two (or three or four or five) can hardly be called a "head crash". Think about it. After touching the bed with the head, you can go a further 0.3-0.4mm even with a completely fixed bed, without any trouble. 0.3-0.4mm equals about 760-1000 steps.
But even ignoring that (as hard as 760-1000 steps are hard to ignore), the Z current on my setup is set so it cannot do any damage even if it continued pressing against the bed until i hit the kill switch. And that's with an Arcol.hu head, one of the least sturdy heads available.
And even ignoring THAT, i have it set up so it lowers the head about 1-2mm above the bead after a home. And then i hit the -Z button a few times and issue G92 Z0. Which is 4-5 mouse clicks that ALWAYS guarantee that the Z is adjusted right, compared to spending days designing mechanical Z adjustment setups and then fiddling with thumbscrews.