Simple Touch Plate Probe / Build and Use on bCNC

Ok I’m going to make the touch probe for the CNC machine using this 3 pin aviation panel mount. I’m just sticking with the format of shielding and luckily I’ve got a bit of wire that I can use to shield here.

I noticed when I solder this particular type of wire, the sleeving shrinks a little because of the heat. This might be because I’m using thin solder and keep the iron on the wire core for too long.

So this doesn’t become a problem later, once the wires are tinned, I snip the ends down a little so I don’t have too much metal exposed.

I use heat shrink to neaten the joins and check that there are no shorts using the voltmeter.

I soldered a crocodile clip to one wire end, and crimped a ring terminal to the other.

Ok I need to decide what I’m going to use as the touch-plate now. I’m going to use a piece of aluminium angle bar as the touch plate for now. Extruded aluminium is pretty flat so variation along the piece will be minimal.

And the angle will also help keep the aluminium flat, but I need to tapper this so it doesn’t get caught on the incoming spindle.

Ok the wire that’s meant to be the shield is making contact with one of the other wires. Obviously I haven’t done a good job here. So I’m going to cut this back and un-solder it.  Ok I’ve re-soldered it.

I’ve actually written the code here that I need to write after I’ve done the probe sequence.

To Probe in bCNC I had to position the bit above the area I wanted to probe, and then set the x, y and z coronadites to 0. I then set the probe along z direction to -10, although that could vary, and made sure the touch plate hadn’t moved away from the soon to be incoming bit.

I pressed probe and once they made contact and stopped I typed the command G92 Z1.5 into the command line. G92 sets the position of the bit end, and z1.5 is the thickness of the touch plate along the z axis.

I then raised the bit, removed the touch plate and moved the spindle to the new origin.

I then use my feeler gauge to check the remaining distance between the waste-board and the bit, and reinput the g92 command with that difference.

Thinnest one, which is 0.01mm.

So if I write G92 Z0.1 now it should move down a little bit further. That doesn’t go in (0.1mm). Lets try a thinner 0.02mm. It’s catching ever so sightly. That’s bang on.

I’ll measure that again. That’s 1.49mm, 1.52mm…

I may have not held the aluminium touch plate down well enough, but the thickness does vary slightly. Alternatively I look out for a gauge blocks and use that as the touch plate. Anyway don’t forget to sacrifice a thumb and thanks for watching.


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