Live Z calibration Weirdness
Hello,
I Got my Mk3 kit in a few days ago and so far Everything has been pretty amazing. This thing is WAY better than my POS Tronxy m802a. I did run into something weird though. After doing my original z offset calibration, I ended up disassembling the Y axis. I had over tightened the bearing on the carriage and was getting some binding. After I put everything back together, I re-ran the XYZ Calibration, but I didn't go back and re-run the first layer adjustment. Instead, I started a print for the SD card. I used the live Z adjustment during the first layer which worked fine, but decided to restart so I stop the print. When I restarted the print, the Z offset was back to where I had started, the the Z offset number was still reflecting the adjusted calibration. I tried adjusting the Z offset a few more time during the print, but the same thing kept happening. The Z offset would always start in the same spot, but the adjustment number was getting lower and lower. I decided to go and run the first layer calibration and if you haven't guessed, the nozzle was almost digging into the PEI. I was able to adjust it here and the Z offset seem to be calibrated now. Has anyone else experienced this before? here is a summary of what happened.
1st Print: Z offset .2mm too high. used live z to adjust to -.640. Ended print
2nd Print: Z offset .2mm too high. used live z to adjust to -.840. Ended print
3rd Print: Z offset .2mm too high. used live z to adjust to -1.01. Ended print
Ran first layer calibration: Z offset was .4mm too low. Adjusted to -.640
4th Print: Perfect first Layer
Re: Live Z calibration Weirdness
Did the printer completely cool down between prints or where you restarting the prints one right after the other? The sensitivity of inductive probes changes based on their temperature. The PINDA2 is supposed to help address this by allowing the printer to adjust for the temperature of the probe unit, however on my Mk3 I have found this to not be functioning as well as advertised. To adjust for this I utilize the same process I use on my other printers which have standard inductive probes. before starting a print, I position the extruder close to the center of the build plate and preheat the printer. Through trial and error I have found Z-Offsets that reliably work for the different material print temperatures I use. For example when printing with my PLA temperatures I use -1.32 and when printing with ABS temperatures I use -0.93. Initially I attempted to identify the Z-Offset for immediately after the printer heats, such as when starting a new print with a cold printer, however I found the temperature induced variance occurs to quickly and would require waiting for the printer to cool down between each trial. After switching to the preheat method I found that, in my case, about 20 minutes of preheating results in regularly repeatable results which also work for a second print, immediately following the first.
Re: Live Z calibration Weirdness
keith,
This appears to be the PINDA temp which is listed here https://github.com/prusa3d/Prusa-Firmware/pull/552 please add to the comments to help get this fixed quicker
The Latest Firmware can be found here https://github.com/prusa3d/Prusa-Firmware/releases
Open Firmware Issues https://github.com/prusa3d/Prusa-Firmware/issues
Re: Live Z calibration Weirdness
Hello,
<snip>
After I put everything back together, I re-ran the XYZ Calibration, but I didn't go back and re-run the first layer adjustment.
<snip>
Had you ever run the first-layer calibration? Did you reset your firmware at some point during the disassemble/reassemble process? There is a 'magic' GCode sent when running the official First Layer Calibration test, and without it live-z will be completely ignored. So if you breezed through the menu message 'first layer adjustment needed' (something like that) it will not record your live-z setting between prints until you run their official command through the LCD menu. In practice this means that you will keep adjusting and adjusting, then as soon as you run the calibration the firmware will finally respect your changed setting and your nozzle will be much further away than you expected.
Ran into this issue as I prefer to do my own calibration prints - don't get much out of the wavy line method. Gave my PEI a nice scratch for my efforts. BTW the GCode is, I believe, G87.
Re: Live Z calibration Weirdness
I just built my MK3 this weekend. I honestly am underwhelmed by the included live Z calibration print. The line and the small square were too hard for me to see clearly and make the right adjustments.
I used the method from https://shop.prusa3d.com/forum/prusa-i3-kit-building-calibrating-first-print-main-f6/life-adjust-z-my-way-t2981.html instead and had MUCH better results.
I just kept adjusting by 50 um until I got close and then starting using smaller increments until I found the sweet spot. It helps to have a caliper to measure the thickness of the finished squares as well, but not completely necessary.
I tried to avoid any complication from the PINDA being affected by the bed temperature between prints by moving the extruder up and preheating manually before starting. Seems to work pretty well.