K40 doesn't home anymore

I’m running an M3 Nano board in my K40 and everything worked perfectly until suddenly the laser at ‘home’ moved 50mm down and 50mm to the right instead of to the top left corner. Even when switching on, it always moves to the 50/50mm position. Everything else works as usual, even the jog function works correctly.

Does anyone here have any idea what the problem could be? I have cleaned the end stops (although the laser moves away from them) - this has not changed anything.

I may add that this happened while the laser did jobs for about a hour or so. So it wasn’t “switch on and error” but rather out of the blue while working.

I can move the laser head manually to the home position and work as usual. But on every switch on and “home” it moves 50mm down and to the right. And it tries to go further even when it reached the end of the rails, resulting in nasty und unhealthy rattling of the belts…

Any solution would be very welcome.
Thanks an advance,
max

Does it move to the 0,0 position and then to 50,50, or does it just stop 50mm into each axis?

Can you post a short video showing this in action?

It just starts moving and stops at +50/50. I’ll make a short video.

Have a look here:

I should also mention that I control the k40 with k40whisperer under winxp. However, since the head also makes this movement when switching on without a computer connected, this cannot be the reason.

Test you end stop switches and cables. Maybe one or both have become closed/triggered(open circuit) and look to be triggered by the firmware so the firmware does the safest thing and moves away from the corner trying to change the switch state.

Hmmm, both at the same time? I can move with the jog function freely in all directions. If it’s the endstops then this should not be possible in directions up and left, am I right?
I already cleaned them, but i will check the wires too.

I don’t know your wiring, both can fail if your wiring connector came loose or the common ground wire broke. But why focus on one of the 2 options I provided?

interesting, how do you “clean” your end stop switches?

These are optical switches.
I didn’t meant to ditch one of your suggestions. I will check switches and wires.

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Besides checking wires and connectors it would be a goal to actually validate they are functioning. If they have an LED which lights when triggered that might be good enough once wiring has been inspected. If they do not have a ‘triggered’ LED then it might be necessary to put a voltmeter on each of the signal wires to measure and “see” the switches are triggering.
Anyone else can chime in if they have experience testing optical limit switches on a M2/M3 Nano board. My experience is with GRBL based controllers.

To learn more about optical limit switches here is a write-up Don did some time back - Don's Laser Things: K40 Optical Endstops

Using a voltmeter:
For a K40, the limit switches are Normally Closed (NC), so when the gantry is away from home position, the X and Y pins should each measure around 5V relative to ground.

When the gantry is in home position, the X and Y pins measure approximately 0V.

Ah, each home operation goes 50x50 further from the origin, regardless of where the head is when the home operation starts.

My guess is that the switches are triggered and it’s trying to move away until they aren’t triggered, so that it can re-home, and giving up when it moves that far.

So I’m with @dougl on this one, to see whether the switches are actually triggered even with the head moved away. And cleaning the optical switches was a sane first step, but doesn’t mean that they work, so testing them electrically makes sense.

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Thanks for the explanations. I will check everything in the next days and report. My guess is: something is broken in the wiring, because the error appears on both axes the same instant. But we’ll see…

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A common problem is that the metal endstop flag gets bent and damages the sensor when it enters its gap.

This happened to mine and I replaced the switches with mechanical ones. It wasn’t easy, but they have worked well ever since. (Knock on wood).

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Hej guys,
today i finally had the time to look after my k40. You were absolutely right in your suspicions - the problem was with the end stops.
So I had a serious conversation with them and explained that I was not willing to accept that they no longer wanted to work.
Well - something like that.
It was the ribbon cable that was no longer fully plugged in. It had slipped out a bit on one side (for whatever reason) which meant that the switches could no longer give a signal.
I reattached it properly and everything is back to normal again.
Thank you so much for your help. This has helped me again to understand a little better how my k40 works.

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Yes! The joy of learning from fixing things that break… :heart:

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