MPCNC permanent z probe

So I’ve had nothing but success with z probing using alligator clip on my tool, but having to clip it on / off is a slight inconvenience.

Using a dw660, I’ve been wondering if mechanically there’s a way to keep the z wire on the spindle even while it’s running.

Has anybody given this any thought and made any attempts?

I had considered a carbon brush (like from a brush motor)

Best guess would be to take the shroud apart on the top. Use a multimeter in ohm mode and probe from the collet to something metal, non-spinning, and that definitely will NOT have any electrical potential on it. You could then potentially attach a wire to this point and feed it through the vents on the shroud.

Just an idea.

But in my opinion it’s far safer to stick with the alligator clip method.

Try some magnets they work well. With mine as long as everything is on the same circuit no clip or magnets needed I checked with foam and aluminum tape


I agree with @timonjkl. I just stuck a magnet into the jaws of the alligator clip and toss it at the collet when I need to zprobe. Removing it is as easy as giving it a tug.

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I wonder if it isn’t already grounded. It may work to just leave it off.

Since it is spinning, it would have to be electrically connected through the bearing.

Neither my 660 and 500w spindle need a connection when plugged in they don’t need to be turned on either but it works with it on too. Not all mill coatings conduct electricity or one with a lot of pine burnt on it

One problem I would be worried about is if it makes poor connection to ground through the bearings, it might appear to work until it doesn’t and then one day it crashes into your workpiece amd stretches your Z coupler.

Another option would be to have a known-height endstop switch that mechanically detects the bit instead of conducting through the bit.

Couplers are cheap. I accidentally pushed a vbit through a piece of oak once. It didn’t survive being pulled back out. Alligator clip popped off when I turned to hit z home.

I ran a alligator clip at 30000 RPM once no twice still haven’t found it.


With MPCNC it compresses the coupler and lifts the frame out of the legs and you have to relevel the bed.

Am I the only person who built one of these? It works on capacitive touch so no probe on the tool needed and works with any tool so long as it’s metal. It actually works on fleshy tools too (fingers) but that seems to be less useful. It’s spring loaded so even if it fails to detect the tool (which it hasn’t so far in 70+ homing cycles) you would have a second to hit the E-Stop before it crashes into the board. It even has a little light off to the side for visual confirmation that the probe as been engaged.

I sacrificed one of the holes on my board in a little used area and just leave it there all the time.

I can attest that you don’t want to crash Z into the bed, re-leveling is no fun.

Here’s a video of mine in action.


I’m interested do you have a build page I would like more information on this

I seriously considered making one of these. I had not read about it on the forums yet, so I thought it would be a non-standard solution which might have some issues I did not foresee. That’s why it dropped pretty low on my list of ‘things to try’.

My experience with the alligator clip kind of probe is a bit hit and miss, and it’s more work than just running some gcode that always works.

That’s very neat! I’d also like some more info on how you built it.

Does it home to the same Z level regardless of the size and shape of the tool? Larger end mills have more metal, so they might trigger earlier than thinner end mills, or not?

My main issue is that I use g38.2 to find the corner of metal stock. So switches in general wouldn’t work for me.

Very cool. I’m sick of messing around pulling paper under the bit while adjusting the z-height. Time to upgrade and thiis looks like a great option. Do you have a vector to a design page?

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Two things I’ve considered doing, option 1 build a pyr0piezo. That would give you a mechanical switch that’s quite small and accurate that doesnt need any connection to the router. Option 2 is use a grounded router and read the router ground. You could add a ground brush to the dw660, probably wouldnt be too hard to come up with something you can 3d print to attach a brush to the shaft, maybe a replacement for the nose peice with the button to lock the spindle for bit changes… reuse the dw660 brush and brush springs so the parts stay the same.

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Hey, sorry for the slow response.

I don’t have a build guide yet, but would make one if there’s interest. I was also thinking of getting custom PCBs made to solve the rats nest on the side.

So far I haven’t had any issues with Z levels, it’s gone to the same place each time regardless of tool. Mind you, I only use a quarter inch end mill, an eighth inch end mill, and an engraving bit (which I haven’t actually tried with this system yet). The capacitive response is exponential in the last couple tenths of a mm as it approaches the endstop so I haven’t had issues with repeatability independent of the tool used.

@Doug_Bailey I’m not sure what a vector to design page is, can you elaborate?


@jimprince Hi Brad, would you mind in taking a look in this thread:

I started had very nice inputs but I could not make it work. Probably you can help me :slight_smile:

Please write a built guide for your capazitive probe!