This is my Z touch probe.

This is my Z touch probe. It is made from 4 mm garolite (fiberglass board) and two pieces of spring steel. Pallet shipper strapping works well. One of the leaves needs to have a larger hole drilled and a plastic washer or other insulation to fill the gap. I use a normally closed loop for all my homing and probing. I also plasticoated the end of the longer leaf to make the actuation rely on the separation of the leaves and not a ground from a metal bit. (That was happening) Electrical tape works too. This gives me the ability to probe with other things besides metal bits. I have several screw on attachments that allow me to use things like; paint pens, rotary needles cutters, Roland vinyl blades and what ever else I can dream up.

I was using the flat plate with a alligator clip on the tool method. I was having problems with electrical noise causing false positives. I decided to go all normally closed with capacitive filters to dampen the noise.

I works really well and is very accurate. I decided to use sketchup picts because it was easier to see how to build it.

Nice. What firmware are you using? What set of commands you execute?

I use GRBL 1.1f Firmware.

This is the way I started out. I found that Normally open circuit can be randomly activated due to system electrical noise. So I went to Normally Closed with signal high. I also added a capacitive filter to filter out noise. I’ll post that circuit when I find my notes.

Macro Command is:
G38.2 F300 Z-100
G92 Z7

Where “F” is the speed of the movement towards the probe. “Z-100” Is the distance the movement will go before it times out. “G92 Z7” sets the thickness of my offset to 7mm. To measure the Offset run the G38.2 F300 Z-100 command. That sets Z to zero. Then you remove the probe and manually jog down until you touch the surface. The difference is the offset. You can make fine adjustments by adjusting the number up or down.

I did find that since it is a mechanical switch you need to pay attention to where you touch the bit to the probe. I aim for the center of the black plastic coating. Closer or farther out changes the zero ever so slightly. I sometimes use that to my advantage too. If I want my bit to shave off slightly more I just probe closer to the end.

This is my simple noise filter. Uses standard 100 nF Caps and 4.7k resistors. Gleened from this post.

There are much better filters that could be used. This one does a pretty good job. An Optoisolated filter would be best. (Ain’t nobody got time for dat)