Good evening folks. I've created a new folder under our M2 repo on our Github (https://github.com/MakerGear/M2/tree/ma ... auto-level
) called "Experimental Parts", which will be the home for any semi-official/testing upgrades, including the auto-level probe and bottom Z endstop setup.
The "Z Probe for auto-level" folder contains all the current experimental parts. There are two different probe mounting systems - a very simple bracket to simply test out the bed leveling features (mount a microswitch at the bottom, mount the bracket to the filament drive mounting hole closest to the idler shoulder bolt), and the more advanced "hex" probe. The hex probe requires a few extra bits of hardware, in addition to the prints - the new extruder motor mount has two M3 nut traps and counterbores that will allow the probe body to mount to the side of the EMM with two M3x12mm bolts; the probe body requires two M2.5x10mm bolts to secure the microswitch to the part, and also needs springs and a guide rod (addressed a bit below); the probe needs two bolts, M3x8mm preferable for the actual probe tip (to avoid melting the PLA tip if probing on a bed heated for ABS printing), and M3x12~20mm for the probe "handle", which activates the microswitch and allows manual control. The probe needs a spring to force it down strongly enough to activate the microswitch (and hold it in place while inactive) - I used a 3mm Allen wrench as a guide rod, and the springs from two pens (an orange and a purple Pilot G2, if you want to be that attentive to detail... this configuration may not have quite enough force/throw, however).
While idle, the probe is lifted up and rotated CCW (when looking down at the printer) so that the "handle" bolt sits in a relief in the probe body; the spring force keeps it in place. In use, the probe is lifted slightly and rotated until the handle bolt is in the main channel, and gently brought down to contact the microswitch. When commanded to probe Z, the printer will raise the bed until the probe bolt head hits the bed, opening the microswitch; the bed will drop a bit and slowly touch the probe again (standard homing "double-tap" behavior). The microswitch is plugged into the Z-Min header on this printer's RAMBo, as I'm using this printer with a Z-Max endstop/homing direction by default (which I think may be preferable when using the Z probe).
The firmware in that folder is currently configured for homing Z towards Max (so down, hitting/activating an endstop at the bottom of the printer).
I'm still wrapping my head around all the offsets that are in play here (M851 sets the Z probe offset, "M206 Zn" sets the Z _home_ offset, and there are compiled probe position/range values), but the firmware as it stands should work. I believe that the process is to set your M206 Z home offset first (if homing to Max); then use M851 to set the vertical distance between the probe activation point and your standard bed:nozzle gap (~-17.9mm on my setup, IIRC).
I don't believe I've missed anything critical here. One note about the optical flag - if printed in our Blue PLA, it may be IR translucent enough to not trigger the optical switch; I haven't tested that thoroughly yet, but adding a piece of standard black electrical tape was sufficient. The flag itself can easily be trimmed down to fit a different endstop setup (you don't want the bottom pressing against the endstop assembly when the Z motor is disabled) - I trimmed mine down to a layer or two below (/above...) the chamfer on the flag tip.
Let me know if I've missed anything here, or if you would like .STEP or other formats for the parts.