Mechanical Limit Switches for the ShapeOko

So in this post – Limit Switches for the ShapeOko – I installed some optical switches as limit switches.

They were working pretty well until I did a job boring 66 largish holes in some MDF. That made a lot of dust – more than my vacuum could keep up with – and the dust got into the limit switches and made them trip.

I also had some random trips, and some that appeared to be related to static electricity. I would touch one of the rails and the machine would stop with a limit switch error.

This was less than optimal.

So I bought some mechanical snap switches from McMaster-Carr and mounted them up.

I was going to do some fancy bent metal pieces with bolts through them to trip the switches, so that if I over-ran them they would not get damaged, but then I looked at the machine.

A while ago I replaced the motor mount plates with the v2 plates. These plates have nice little slots near the edges just for mounting limit switches to. And the roller will hit the end plates and trip the switch about 1/4″ before the plates will hit. It almost looks like it was designed that way!

So I bought some #2 screws and nuts and bolted them up.

Here is an in-progress shot – the new switches are mounted, but the old wires are still hanging around.

01-outI got them all mounted up, but I needed to make a stop for the far end of the X axis so that my dust shoe and router would not run into the end plate. This is what I came up with.

02-stopA little bit of re-wiring and this is what we get. This is the X axis wiring. The switches are wired in parallel. Looks like I should clamp that cable down a little better.

03-new-x

The one concern that I had about the mechanical switches was around the repeatability and accuracy of location that they would have. The optical switches were pretty dead on. When you homed the machine, it was the same zero every time.

So I setup my dial indicator and tested it. I’m happy to report that homing the machine and then moving to the same position was within .001″ every time.

05-testing

I did not change the switch on the Z axis yet. I have plans in my head for re-designing the Z axis and didn’t want to do the switches twice. If I have more random trips I’ll reconsider doing the Z.

There is one interesting side-effect with the mechanical switches: you can hear them trip with a little click sound. When you home the machine it does a some back and forth hunting at slow speed to find the exact location where the switches trip and you can hear them clicking on and off.

Fascinating.

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