Troubleshooting a C Marker Trip Problem

A Thermwood CNC owner gets help tracking an error message to the hardware issue that triggered it. January 4, 2014

Would anyone be able to help? Error 1500 X axis did not find c marker on ramp down. Any ideas on how to fix?

Forum Responses
(CNC Forum)
From contributor L:
You should be talking with Thermwood. Visit their forum and ask the question.

From contributor B:
It is best to talk directly with Thermwood's techs. The call is free.

From contributor L:
That's even better. Talking directly to the techs.

From contributor S:
Did you get down and look for the physical c markers on the x axis? They literally look like a c shaped piece of metal with wires on it. When the moving part of the axis comes back home, a piece of metal is supposed to go in between the c marker and send the input to the controller. Is some junk bending the c marker or the piece going into it? Are the wires intact on the c marker? Look in the Thermwood manual if you don't know what to look for. But it is pretty self-evident when you see one. Also Thermwood tech support has always been helpful when I've called them.

From contributor B:
Just to clarify, I believe what you are referring to are Hamlin switches. They are somewhat similar in general function to proximity sensors (but less expensive) and are not the actual C-marker. Part of the home sequence is to signal the controller when to start looking for the actual C-marker, which is itself a part of the encoder.

You suggestion to look for a broken Hamlin switch or for junk interfering is sound. It could also be knocked slightly out of alignment - in which case the controller could reach the count limit before finding the C-Marker (normally this is a fair amount less than one revolution).

From contributor S:
I stand corrected. What you call the Hamlin switches are what Thermwood calls the Home switches. After the home switch gets tripped, the controller calls for deceleration and the controller is supposed to look for the c marker, which comes once a revolution of the screw. After the c marker trips it's supposed to reverse the axis and return to the c marker to home the axis. Error 1500 means the c marker wasn't found during deceleration. The machine manual tells how to realign the c marker.

From the original questioner:
Cheers for the help everyone! Will know what I am looking for next time.