Calibration crashing into bed on Point 4/9  

Re: Calibration crashing into bed on Point 4/9

Since it was working fine for 4 months, it could be a bad part or two. Here are some things I would check in order of likely-hood.

X-Axis Belt - Check for any missing teeth on the belt. Since it finds the first three just fine, you could be skipping teeth.
X-Axis End-stop - Your end-stop may be wearing out and is now intermittent. No real way to test an intermittent end-stop, so up to you if you want to order one and change it out to see if its that.
PINDA - The probe may be faulty. I don't really think that is the case, but stranger things have happened.

Hope this helps

Re: Calibration crashing into bed on Point 4/9

Thanks for the ideas.

The belt looks fine. I don't run the printer 24/7 or anything. Just hobby stuff.

The limit switch could be tested with a DMM to make sure it closes correctly. I use those switches in my job and they are usually rated for hundreds of thousands of cycles. So, unless I got a bad one I kind of doubt the switch has worn out. It's worth a try though.

I was finally able to get a calibration to run through. When it works it works fine for a while. When it went to step 4/9 it just went to the correct location of the sensor in the bed. Then it ran through fine. Then at some point I'll have this problem crop up again.

As far as the PINDA probe is concerned, is there any sort of diagnostic that can be performed on it with a DMM or oscilloscope?

I may be one of the few people having this problem but I also suspect a firmware bug in the calibration code. This problem really seemed to crop up mainly after I installed v10 firmware. I was about to try to switch back to v8 to see if the problem goes away but then my calibration miraculously passed and I have an important part I want to print before I experiment further.

Re: Calibration crashing into bed on Point 4/9

Something else I was thinking about on the endstop switch, your switch may have moved closer to the motor and isn't triggering all the time correctly. Try loosening the switch and hold it to the right as you tighten it. May have had the X-axis or Y-axis carriage hit it hard enough to move it slightly.

Re: Calibration crashing into bed on Point 4/9

Check to see if the threaded rods that connect to the prusa frame are still level, a bump or constant usage vibrations could have popped one up.

Re: Calibration crashing into bed on Point 4/9

Thanks for the idea. Do you mean the threaded rods that create the lower frame or the threaded shafts for the z-axis steppers? If you mean the latter, one thing I notices is that the threaded shaft on the right side sticks just a little more out the top plastic support than the one on the left does. The top of the one on the left is basically flush with the top surface of the orange plastic mount. The top of the one on the right sticks maybe 1-2mm above the top plastic piece. Could that be an indication of something else being off?

Re: Calibration crashing into bed on Point 4/9

On mine, the threaded Z-axis rods are out about 1-2mm above the orange guide. They should both be out an equal amount. If one is lower than the other, you should start there and try to find out why one is lower. Those being at different heights may be causing a problem even though the firmware can adjust for small deviations on the rod heights.

I believe michael.e3 was referring to your y-axis threaded rods. The fram sits on top of those threads and one may have loosened and moved.

Re: Calibration crashing into bed on Point 4/9

Hello there. I have the same problem. At point 4/9 my noozle kissed the bed. Every time after the first print.

After that I press reset and start the print again and it works.

I think theres a problem in the firmware?

Re: Calibration crashing into bed on Point 4/9

So guys. Please take a look at this.

I don't think that's a hardware problem.

Re: Calibration crashing into bed on Point 4/9

This looks a lot like a problem I'm having, except that it ran quite a few prints before it started crashing on point 4. I've tried resetting, but that doesn't fix it. I run selftest and that passes, but then I run Z-axis calibration. On the first point it is fine, on the second, it seems to be touching the bed, definitely touching on third, pushing bed down. I usually hit the off switch before point 4. It's created quite the little dimple in the bed there. What is strange is that the printer ran fine for several days of nearly continuous printing before this happened. I checked the P.I.N.D.A., since that's been the cause of issues before, but it seems to be exactly where it's supposed to be and I can't move it. I'm really perplexed as to what is plaguing me this time. I'm sure it's probably something I've done wrong. Any suggestions are appreciated.

Thanks,
Ray

Re: Calibration crashing into bed on Point 4/9

I'm having the same issue - ran through testing the endstops and PINDA with support, all was okay. They asked for a video, which I've provided, but I immediately reset when the calibration started really pressing into the bed (I've got a nice divot there, and I don't want to damage the bed even more). Given it detects the first three points fine...is is possible...I don't know...the 4/9 point has become demagnetised or something, so the PINDA doesn't pick it up?

Re: Calibration crashing into bed on Point 4/9

I dont know what the problem is but after pressing reset it worked but my Heatbed was now damaged... there was now a big spot at this point. Damn no respond from Prusa here :/ Recalibration has no effect at my Prusa. I tried it a few times. This heatbed costs 94 euro :/ and that problem with a printer that costs 760 euro 👿

Re: Calibration crashing into bed on Point 4/9

I ran a full calibration, and it's clear that the middle line of points 4-5-6 are the problem here: 1-2-3 calibrates fine, as does 7-8-9. Given there is absolutely no reason for this to have randomly become a problem (or the sensor needing to depress the bed to detect the point), this must be some kind of hardware fault. I'm just not sure what kind.

Full Calibration Here:

Re: Calibration crashing into bed on Point 4/9

After a full reset (and total failure on the initial XYZ calibration when I know it's perfectly aligned), I ran a couple Z calibrations. It does seem to be off axis slightly, which doesn't make sense...until I noticed that a bit of plastic at the back seemed slightly crooked. I reached out and...

Check your endstops are in place - I did, but I didn't realise that a crack had developed and it was being gradually nudged out of place. I'm hoping this will resolve the problem, but you never know.

Re: Calibration crashing into bed on Point 4/9

After printing for a few weeks perfectly - mine is now doing exactly this - slamming the head into the bed at point 4 / 9. It has to be a software problem. Going to try a firmware update (I'm on the .10 FW, and .11 came our recently)
😥

Re: Calibration crashing into bed on Point 4/9

After a full reset (and total failure on the initial XYZ calibration when I know it's perfectly aligned), I ran a couple Z calibrations. It does seem to be off axis slightly, which doesn't make sense...until I noticed that a bit of plastic at the back seemed slightly crooked. I reached out and...

Andrew, what is the black thing on the left X-axis lead screw? (Pause your first video at 0:24. ). The left side appears to have a nut/extrusion on top that the right side does not? Running the X-axis carriage all the way to the top and letting the motors skip is supposed to level both sides, however it appears that on the left side you have a nut meaning it stops running before right side, knocking the whole z-axis out of alignment rather than aligning it.

Probably not the only thing going on here, since it fails for all of the middle row, but I suspect that the firmware is using the level from the first point to guess the level of the subsequent points. It lowers until it either detects a point (and stores it) or keeps going to a preset value below this (IE the 2/3/4/5.. point will not be any lower than X mm compared to the first.) This could be set up in such a way that it would stop the nozzle from crashing into the bed if the probe misses. However if your z-axis is badly out of alignment AND the probe misses the point, it would crash into the bed before reaching this lower limit as set by the first point.

On your second video (where it completes all 9 points but crashes on 4-6) does the screen say the calibration was a success or failure? Watching in slow motion (0.25 speed) when it first crashes on point 4 the left screw appears to still be lowering while the right screw appears to rising. If the firmware detected a rise in the bed from point 1 > 3, because your z-axis is higher on the right side, then I would have expected this to be the other way around.

Re: Calibration crashing into bed on Point 4/9

For what it's worth - upgrading to the .11 firmware and calibrating from the beginning has fixed the problem for me.