Making the touchplate more funner....

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Rando
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Location: Boise, ID
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Making the touchplate more funner....

Post by Rando »

[Edit: based on your machine, this might work. If it doesn't, let me know and I'll try and figure out how to make it work on yours.]

All:

This is a minor modification I made to my Rocker 60th (HD2+) machine that you might find useful.

For a lot of my work in aluminum, the work piece is held in a nice Kurt D688 vise, bolted down securely to the bed. Yeah, it doesn't give anywhere near the machine's full range of motion, but I also don't have to deal with clamps or spoil board, and so on.

Ever walked up to your machine and gotten one major static shock from it? My worst ones were when doing acrylic. On investigating, I noticed that the bed, even with the metal angles as supports, is electrically isolated. Not grounded, not anything. The grounding wire to the stepper doesn't seem to connect to the bed, but that's not entirely surprising it would have to go through the bearings and stepper shaft, and so on. So, I fixed that, attaching a wire from the bed to "earth ground". Yeah, there's an actual copper water pipe nearby. That solved the static issue for me.

Then I tried to use the touchplate....no dice. Say what? It turns out that the "probe" part (with the magnet) is connected to the controller box ground, which means that the "sense" line is actually the plate. Well, when that plate sits on the vise or aluminum mounted in the vise, it completes the circuit through that anti-static ground I added, and appears always touching. D'oh! Hmmmm....okay, so that isn't going to work....

Next up, I remembered that the bed/vise/material is really only grounded for the static...and static charge accumulates very slowly, one cut chip at a time. That means I can insert some resistance into the ground wire, hopefully enough so that contact doesn't trigger the touch plate, but still enough for the static to bleed off. Based on my testing, a 450K Ohm resistor worked great.

Check the below schematic for what I did. One thing to make sure of is a good connection from the power cord ground and the controller box to the spindle and bit. This is a must, and you might want to run a wire up to it if your router/spindle doesn't have a ground connection. At the back of the controller, I attached a standard 1/8" headphone jack Y connector (full stereo both sides, though I suspect it wouldn't matter if it was actually a channel-splitter), and then plugged the touchplate into one side. On the other side, I took the tip and ring connection that also connects to the probe wire, and ran that straight to the controller metal box. The sleeve connection I ran directly to the bed, while the 450K resistor goes from the bed to earth ground. There's an added benefit to using the Y, even if you don't make this mod: the controller card jack doesn't get damaged if you plug/unplug the touchplate.
Touch probe modification schematic
Touch probe modification schematic
Using that method, I can use the bit and aluminum material without using the probe or the touch plate, and never having to worry about the probe falling off. And, if I'm doing insulating materials like wood or acrylic, I can use the touchplate, and not worry if the plate touches the vise or bed or clamp, since it won't get false touches. And, bonus! It actually makes the touch probe redundant, because the router spindle and thus the bit are always connected. If you've ever watched in horror as the magnet pops off during the touchoff, you know how much a relief that will be. Schweet!

Hope you find this useful.

Thom
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ThomR.com Creative tools and photographic art
A proud member of the Pacific Northwest CNC Club (now on Facebook)

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