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Simple Touch Probe
Thanks to johank for pointing out the error in the original design! There is now a 3D printed component to hold the centre contactor together. Use a small blob of super glue to hold the M6 nut and the 6mm rods into the contactor.
The spring should be tensioned to pull the contacts lightly together. With stainless components the resistance of my probe circuit varied between 20ohms and 200ohms depending on spring pressure. Set the spring as light as possible while still reliably triggering your controller input. If the spring tension is too high the probe will apply more force to the bed before it triggers and this will reduce your accuracy.
The probe stylus is made from M6 threaded rod or a long M6 bolt. I ground the tip to a 30deg point with a slightly rounded tip, but you can make any shape you need. You can also make threaded tips which screw on, or even 3D print a custom stylus.
Heres a few videos of the probe in action: