X-axis intermittently fails to find limit

[walter_davis]

I’ve been pulling my hair out about the homing sequence lately. The problem is, it comes and goes, and while I have found a way to un-stick it when it happens, I am at a bit of a loss as to how to solve it long-term.

Occasionally, during a homing cycle, my Shapeoko 4 XL will drive into the X-axis stop in the back, refuse to acknowledge the (working, light on) homing switch, and just keep trying until it gives up. I used to hit the stop button in Carbide Motion when this happened, and then send $h to re-home, but often I would also need to power off the machine, drag the carriages out into the middle of the work area, and then re-power the machine and re-home it. This only worked about half the time.

The last time, I discovered that if I “flick” the bundle of connectors at the right side of the X-axis with my finger while this is happening, the limit switch will suddenly re-appear to the controller, and everything will sort out. But short of disconnecting and re-connecting everything, and then praying that this doesn’t repeat, I am at a loss for finding a more long-term solution.

If the issue is a connection that has come loose, then why would that happen? These are strong spring-clip-to-pin connectors, with mighty snap locks forged of real Nylon. They should not lose electrical connectivity or mechanical connection to one another, even under heavy vibration. I have seen these in my car’s wiring harness, for goodness sake. I don’t use the CNC every day, and I’ve only had it for a few years.

If the issue is a conductor that has worn or broken, then is the wiring harness sub-standard in some way? Are solid conductors being worked back and forth until they break? Should I source some extra-flexible stranded wire and re-build the harness? Are there better connectors I can use? I am about to rip everything apart and install grounding (I found some silicone-insulated very-fine-strand 14-gauge wire for that), so it would not be out of my way to replace all the drive cables and sensor cables at the same time.

Thoughts? Suggestions?

[Chaotica (Joel McKenzie)]

If the crimps on the conductors within the connectors are not done properly(like, crimped too much on the insulation instead of the wire or just not tight crimps) this can happen. Since it’s on your X-axis limit switch, that should be easy to identify which cable/connector. You can try wiggling/bending/stressing the cable around the connector to see what it does during homing. As a temp fix while you consult Carbide3D support, you might find a position you can zip tie the connector into that maintains a proper connection.

If you want to DIY, you can get new connectors/crimping pins/crimp tool & re-do the connectors yourself. That’s what I did - cause I love parts/tools & solving problems.