MPCNC Primo Z-Max Switch

I designed this thing to add a z-max switch to my MPCNC Primo. It is designed to work with the same size limit switches that are standard on MPCNC. It works with Burly style mounts, but may also work with others (the lever has to hit the top of the mount). It installs on top of your z-nut.

Is it necessary? Not really, but it's a valuable addition. Let me explain...

Most professional CNC machines can have an arbitrary workspace origin, aka WPOS zero can be anywhere (GRBL, Marlin, etc are the same). However, if you don't home your z axis, your MPOS may be set to zero wherever it was when you turned it on. If that is right next to your spoilboard, jogging down to your zmin will crash the bit. Adding z-max to your homing routine means your MPOS z=0 will always be at the top of your z travel. This is how most professional CNC machines usually operate for safety reasons.

Also if you want to do semi-automated tool changes with a fixed probe location, the machine must know it's absolute position (MPOS) along z to move to the proper tool change and probing heights. By adding a z-max switch, and homing to z-max, you set z=0 at the top of your z travel. Then you can be assured when you rapid to your tool probing location, the head will be at the correct height. For this reason alone, I feel the MPCNC should by default include a z-max switch.

Firmware configs?

Yep, for this all to work may have to edit your firmware config files. Usually you just have to edit your homing routine to include z, and get the z homing direction right with a homing bitmask. Typically the z-max switch is defined to connect to the z-min plug on RAMPS (momentary NO to ground). If that doesn't work, you can check your cpumap file to see what pins are being used for what.

When you go to test the first time... please do so carefully!!! Preferably do a test before mounting the switch, starting homing from the middle of your z travel to give time to react. Hit the switch manually with your fingers, and if it doesn't stop hurry and halt the gcode in your sender software. If the switch fails to stop the z-axis and you are late to halting the sender, the z-gantry will likely break your newly printed switch mount, and the z-screw may end up flopping around the top of your z-nut (not good)... or the router will crash the bed... both of which are not desireable.

[Update: 2-28-2021

I uploaded a v2 stl file, which has a thicker body for more stiffness. Since the z-nut screws were already sticking up into the travel area, I figured I might as well use that extra room to make the switch mount even stiffer.

The v2 file can also be printed without supports, however you should use build plate only supports if you are picky about your counterbores.

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Print Settings

Rafts:

No

Supports:

Category: Machine Tools