I took the extruder block home and sliced a piece off the rear end, so now it doesn't hit the base of the Z stage any more. But when testing that, it turned out that at a specific X stage position, a screw in the Y stage would hit the extruder holder. 'Tis but plexiglas, I can take a wirecutter to it and snip off a corner. Works.
The lower Z endstop is not calibrated for the current height at all. Need to add a better-than-cardboard piece. Unfortunately, it's in a very tight spot -- that's one of the issues with this design: While the printing surface is nice and accessible, the L- and U-shaped aluminium pieces and the multiple layers of plexiglas makes it difficult to get in and adjust things.
Finally after some fiddling got it bolted on - though a broken-off corner on the teflon runner foot -- only in that corner, of course -- made the endstop plate bend forward, so I had to bend it back. Fiddly.
The endstops don't work the way I'd hoped to. At the moment, they seem to be floating, though the bottom Z LED registers nicely, and the bottom X LED registers weakly.
Oh. I had old pin settings on them. After fixing that, it turns out the two Z endstops and the two loose ones are fine, but the X and Y endstops are floating. I wonder if it's a problem with the mounting? Will take one off and try it on its own. Yes, definitely the case for the X endstop. I guess the bits of wire on the back side were enough to dig through the paint and short it. Adding a piece of cardboard helped quite a bit.
I'm also getting a bit concerned about the X and Y stage rail pressors. The X stage wobbles sideways quite a bit, and the Y stage jumps easily up and down. Not easy to fix, particularly the Y stage, due to the construction.
Trying the ReplicatorG calibration block. It seems to expect much higher speeds than I have given in the firmware settings. I should re-measure the speed and put in realistic rates. 4mm/sec is kinda low.
Here's some of the bits I chipped off today and the precision tool I used for it: