z-offset different from front to back.  

This could damage the printer so for your peace of mind contact Prusa Support:

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Cheerio,

Same Z Axis Problem, I think

This happened during my first 1st layer calibration. I adjusted the z-axis sensor twice and it keeps happening. Any thoughts? I'll get in touch with the support team as well, but thought I'd post here too. 

RE: XZ axis skew correction ?

Hi

Maybe XZ axis skew correction is needed...

You can find details in Prusa knowledge base here -> https://help.prusa3d.com/en/article/xz-axis-skew-correction-mini-mini_158518

For sure if it's the case Prusa support will confirm it

JC

Follow up.

I contacted support. They walked me through a lot of the troubleshooting tips mentioned in these forums. Ultimately they determined it was an issue with the y-carriage. They are sending a replacement. I highly recommend the support process. Very helpful, fast and kind. Highly recommend. 

RE: z-offset different from front to back.

Hi,

I've got the same issue and I'm going to contact support. Which part have you replaced?

RE: z-offset different from front to back.

In the end it was an issue with the torque on the z axis screws. I built a second printer and it had an x axis error and it was because the screws were too tight. I'd check that your screws aren't too tight on the z axis first and see if that fixes it. 

RE: z-offset different from front to back.

They sent a replacement carriage, the part that you install the standoffs that hold the heat bed. However, it didn't fix the issue. Prusa Support also asked me to check the extruded pieces to make sure they were square. It was time consuming to disassemble and reassemble the machine. My extruded pieces were square, and to be honest I haven't had time to tinker with it further. 

Please let me know what your experience is like. I would like to get my printer working, I just haven't had the time to mess with it lately. 

RE: z-offset different from front to back.

I'm glad you got replacement part, which will hopefully solve the problem.
However, you say:

Posted by: @matthew-2

...

So far I have:

• adjusted the PINDA sensor many times (with the steel sheet removed)
• .....

-you did it wrong. SuperPINDA must be adjusted with steel sheet on the bed!

RE: z-offset different from front to back.

Thanks for the feedback. You are correct. However, I have gone through all of the calibration with the support team and I am still seeing the issue. 

RE: z-offset different from front to back.

For anyone who might be interested this is what my print bed self test looks like. The front half of the print bed has the correct level of smoosh. However, as it works to the back of the print bed, the z-offset becomes to far from the print surface. If I adjust the z-offset to get the appropriate layer fill, then the nozzle will crash into the bed on the front half on the next test/print. 

So far the support team has had me run through all of the calibration tests, check the tension in the bed screws, check the gantry to make sure it is level, check the zy-assembly, check the rods to make sure they were not bent or damaged, and check the extruded sections to make sure they were square. Prusa support has also sent me a new carriage and build plate. I have built and rebuilt this machine many times. 

This printer is the second one I have ordered and assembled. The first one runs like a champion and I am very happy with it. Additionally, customer service has been very helpful. However, these were purchased for use in my classroom and I haven't had a ton of time to sink into troubleshooting this printer. If anyone has any suggestions or advice, please pass it along.  

I will update with any new information from customer service. 

RE: z-offset different from front to back.

Posted by: @bogdanh

-you did it wrong. SuperPINDA must be adjusted with steel sheet on the bed!

@bogdanh
Can You tell me where You read about that SUPER Pinda must be adjusted with steel sheet on the bed ??
I only found that instruction ---> https://help.prusa3d.com/en/guide/height-adjustment-of-m-i-n-d-a-superpinda-sensor-mini-_154547   and there is no sheet on bed.
Please let me know 😊 

RE: z-offset different from front to back.

I sincerely apologize -my mind was at first layer calibration when I was replying.
I think, for adjusting SuperPINDA height, it actually doesn't matter if steel sheet is on the heat bed or not. On the page you pointed out, Prusa indeed says that sheet should be removed, but I just don't see what difference that would make.

RE:

I hope to have solved the issue.

I had two issues:

1) different z-axis offset from the front to the back of the steel sheet

2) printer didn't hold z-offset value from one day to another. When I started to print nozzle scratched the steel sheet with the same z-offset value I set the day before. An almost good value considering issue #1 and certanly a bit higher as it should be (farthest from the steel sheet I mean). For example one day I print with -0.920 z-offset value and the day before, with the same z-offset, nozzle touches the steel sheet. In the meanwhile nobody moves or touches the printer, of course.

What I did

1) Reset firmware to factory defaults. I've 4.3.3. version and I read (in this forum may be) about troubles using sheet profiles function. To be on the safe side I reset the firmware.

2) I've loosened two screws in the trapezoidal nut on the z-axis middle rod. Just a quarter of a turn not more.

Magically everything was good. Printer keeps z-offset value and z-offset from the front to the back is almost good now. I had to go down much more than before with z-offset (i.e. -0.920 before -1.165 after) but now PLA sticks in the same way in all the sheet.

I still can't believe that all this happened. Is it possible that printer is so responsive to a quarter of a turn on a screw or I'm missing something?

RE: z-offset different from front to back.

Thank you for reporting how you solved the trouble.

.. Is it possible that printer is so responsive to a quarter of a turn on a screw..

I just checked Mini assembly manual, and there's said "Secure the trapezoidal nut to the X-axis with two M3x20 screws.". I've read somewhere, that trapezoidal nut should be slightly loose, so that it has a little free play -which makes sense to me. Means, connection between guide rods and trapezoidal shaft shouldn't be fully rigid. And that's why two oval holes (without thread) should be used to secure the trapezoidal nut.

RE: z-offset different from front to back.

Just got my printer done, and seem to be running into a similar problem. I did have the trapezoidal nut way too tight at first, causing z-axis self test failure. I loosened that up but it's still snug and the self test passed. In getting the initial calibration done, I ended up with a good looking test square. Then on the first print crashed the head. Not as bad as the picture above, but there is a line in the surface of the PEI now. Emergency stop and reset. I made sure to be in Live Adjust Z and backed it off to prevent the crash. The first print is still going and looks good so far, though I think the first layer is going to be ugly--though the part is sticking ok. I wonder if I need to loosen those screws a bit more.

RE: z-offset different from front to back.

On my Mini (and MK3S) this nut is lose just enough, so it can "travel" horizontally if needed (there's no gap vertically).

RE: z-offset different from front to back.

WOW! I was having the exact same issues with my Mini kit. I would calibrate the first layer and it would crash on the next test suggesting the front was higher than the back of the bed. The front would be accurate at -0.350 while the back was accurate at -0.950. I tried everything to fix this including over 8 hours with customer service trying to troubleshoot. They eventually suggested that the PINDA was not sensitive enough and sent me a new one. This did not fix the issue.

What DID fix the issue was the genius idea of loosening the screws on the trapezoidal nut. The screws we'ren't even tight, but I loosened them up just about a quarter screw from the point of resistance and this completely solved it! It looks like that horizontal movement was being impeded, which I have no idea why it would have that much of an effect, but it clearly does. My z offset is now -1.225, but it's perfect across the whole bed.

@spark-2 or whichever king discovered this solution, hats off to you.

RE: z-offset different from front to back.

Okay, finally got some time to try adjusting the trapezoidal screws. Immediately solved my issues!! Two months of tinkering and collaborating and my frustrations are finally over!!! 

Thank you to everyone! I hope this helps anyone dealing with this issue in the future. I am also going to send a reply to Prusa support so they can add this suggestion to their troubleshooting!!