[scott216]

I have an Acu-rite KT-3D edge finder I got from my father's shop as he was getting rid of everything. I would like to use it on a CNC router (ShopBot). The way the router works for touching off is you just close a circuit, usually the end mill touches a aluminum touch-plate. I put an ohm meter on the KT-3D to try and figure out how it works, but it's not clear. The wire going into the KT-3D is just one conductor using a mini banana jack. The shaft of the KT-3D is insulated from the rest. I put an ohm meter across the wire and the touch probe tip and it showed about 25 ohms. When I moved the tip, I expected the circuit to open up, but it doesn't; the resistance does go up to a couple hundred ohms, but it fluctuated a lot. If I release the tip to it's neutral position, the resistance does not return to 25 ohms and it still fluctuates a lot. If I remove the test leads for a second and put them back on, the resistance is again around 25 ohms and pretty stable. This has me thinking there's a circuit inside and it's not a simple open/closed connection. Does anyone know the inner workings of the KT-3D?

Attachment 480274

[CNCMAN172]

Most of these type probes have small contacts inside. Due to its age they are probably corroded, and need to be cleaned with sandpaper or emery paper. This is just a mechanical switch the resistance with a short cable should be very close to zero ohms. Depending on the electronics involved it could be looking for a higher resistance, but I would be surprised. I would expect a hiZ reading megohms and close to zero when tripped.

[scott216]

Even if the contacts are corroded, it should still show as open when the probe tip is moved. I removed the top section where the 4 screws are, but I can't figure out how to take it apart any further.