Brand new prusa mini: Z needs to adjust on every new print.  

RE: Brand new prusa mini: Z needs to adjust on every new print.

mhh could be possible, but i doubt that, because i tightend it good and the diviation happens in both directions. if it was a problem with the position of the sensor itself I doubt that it would accure in a random direction in the small time frame between probing and printing the first layer, because aside the offset the first layer hight is rly constant.  I think in the first place there was a problem with a bad probe, and now the remaining error is inherent with uncompensated probes, because there is a reason why there is a corrected probe used und the mk3 at all.

RE: Brand new prusa mini: Z needs to adjust on every new print.

Try installing the latest firmware that came out on 4/6. The release notes say "Adjustment to Mesh Bed Levelling"

I've only done a couple of prints since installing it so it's too early to tell but haven't noticed the problem since.

RE: Brand new prusa mini: Z needs to adjust on every new print.

I have 4.0.5 firmware.

Here is a picture of it just getting worse over several prints. I also feel like it won't even hold calibration from my initial z-height calibration to the print immediately after now. 

RE: Brand new prusa mini: Z needs to adjust on every new print.

After i installed the upgrade Bondtech heatbreak today i did a lot more testing. Interessingly now the randomness is gone. with preheating i get the same spot on first layer now. and i can consistently say that the difference between preheated and cold is around 0.2mm. Thats in line with what others in this thread already stated. so @ulrike-b i think you could be right and there is a component to the problem from not rly secured probes, because i disasembled the whole printhead for the Bondtech Heatbreak installation. That or the Heatbreah itself improves the heat transfer to the probe.

So i think that it is possible that are 3 different problems play in to the MINDA Probe problem. At first there are a few bad probes where the values are all over the place like mine. Then there is definitly a component from the temperature difference between a hot and a cold printstart.Finaly  there could be a small randomnes caused by a suboptimal probe holder.

But for me the first layers are working fine now, at least for the moment.

RE: Brand new prusa mini: Z needs to adjust on every new print.

@julian_bauknecht

Very interesting results. I've been using the Bondtech heatbreak for over a week now. Unfortunately, it did not solve my MINDA problems. However, this is almost a non-issue for me. I just have to remember to preheat when starting the first print of the day.

RE: Brand new prusa mini: Z needs to adjust on every new print.

Seeing the whole assembly makes me think if people who have a silicon sock encounter bigger problems with the MINDA probe.

RE: Brand new prusa mini: Z needs to adjust on every new print.

Posted by: @geoper2

Seeing the whole assembly makes me think if people who have a silicon sock encounter bigger problems with the MINDA probe.

Can you explain how you come to this conclusion, I have issues and I have a sock --but how do you tie those 2 as cause and effect...

RE: Brand new prusa mini: Z needs to adjust on every new print.

I'm suspect you're aware of this but just in case, the mini's probe is nor temperature compensated unlike the MK3s which is.

RE: Brand new prusa mini: Z needs to adjust on every new print.

idk whats wrong with this printer, after 3 days working fine the z values are all over the place again... I confirmed that the real offset between probe and nozzle is stille the same 0.8mm but the needed z-offest for a perfect first layer jumped from 1,070mm to 1,500mm and diviates as high as 0,1mm again... I am a little bit lost atm, never had such issues with the z probe from any other prointer, idk what i can do at this point... Maby i build a teststand for the Probe and test it seperatly from the Buddy Board with diferent temeratures and stuff, or i try other inductive probes, but will see.

RE: Brand new prusa mini: Z needs to adjust on every new print.

I've had my Mini a couple of days now and finding the Z-offset does need  tweaking. I left it pre-heating for a good 10 minutes this morning and ran the First Layer adjustment and then set off a print within a couple of minutes. When I checked a couple of minutes into the print, I found the nozzle was slightly too high, so needed live tuning again. I really hope Prusa resolve this my offering a temperature compensated MINDA option, or allowing the mk3 PINDA to be supported in the firmware with new mounting plastics. The 32-bit motherboard has the extra pin, not currently utilised, so maybe this will happen in the future?

Texy

RE: Brand new prusa mini: Z needs to adjust on every new print.

Posted by: @oxygen

Posted by: @geoper2

Seeing the whole assembly makes me think if people who have a silicon sock encounter bigger problems with the MINDA probe.

Can you explain how you come to this conclusion, I have issues and I have a sock --but how do you tie those 2 as cause and effect...

I thought the heat from the nozzle differentiates the temperature rise in minda. If the heat is contained the sensor will be heated only from the bed thus making the results different.

I can confirm this problem too in my printer. With a warm minda and calibration I always get good layers. If I start a print with a cold printer the layers are really all over the place.

All the solutions are really just a work around so I hope they fix this problem soon otherwise whats the point of having a sensor if you need to calibrate the first layer every time.

RE: Brand new prusa mini: Z needs to adjust on every new print.

@benji

Hey! I want to confirm, do you still have drifting Z-offset problems even though you did the silicone mod to get your bed super flat?

RE: Brand new prusa mini: Z needs to adjust on every new print.

@nibmaker

Had no effect on MBL. I still have to make sure to remember to preheat the bed. The silicone mod allowed me to print on 100% of the bed, however.

RE: Brand new prusa mini: Z needs to adjust on every new print.

I would not expect the mechanical bed flatness to effect how the MINDA measures the height - the problem is the temperature of the MINDA when it is reading. So what it measures the bed height when the MINDA is say 30'c will be different to what it measure the same point if it is say 35'c - the actual height of that point of the bed will be the same, but what the MINDA thinks it is will be different.

Texy

RE: Brand new prusa mini: Z needs to adjust on every new print.

Crazy thought but will covering the sensor in kapton tape work? I have never tried kapton on a conductive sensor but at the moment my tools are in a place where I can't go due to the restrictions.

RE: Brand new prusa mini: Z needs to adjust on every new print.

@rick-m12

Thanks a lot Rick for the very detailed and well commented code. I completely agree that this is basically the only thing that conquers the Minda probe temperature dependency (as long as Prusa ignores our pleas to support the Pinda probe on the Mini). I have not exactly used your code, but thanks to the good explanation I was able to perfect mine for my personal taste, essentially following your strategy of putting the probe over the middle of the bed at a controlled bed and nozzle temperature for a good time, to generate repeatable temperature conditions for the bed leveling. Besides compensating for different temperature histories (printer just switched on vs. directly after a 16h print), this should also compensation to a large degree for different ambient temperatures, as the the probe temperature is largely determined by the controlled temperature over the bed.

I will do more trials with this solution, but I am rather confident that this will work well. If it does not, I will try to experiment with the waiting time. There simply must be a waiting that is long enough get this right. Take the extreme example of waiting for an hour, then any history of that day must be completely irrelevant. But let's hope it is less than that 😉

RE: Brand new prusa mini: Z needs to adjust on every new print.

The 80 seconds originally used wasn’t enough for me so I went the extreme and set it to 300 seconds (5 minutes), even then it wasn’t reliable. 
i understand that story are now advising the opposite - keep the head away from the bed prior to print start. In the mean time I just tinker with the z level until it is as I want it. I find I tinker a lot first thing in the morning then it’ll be good for the test of the day. Most of my prints takes 2-3 hours. Longer prints I leave over night. It’s a real shame prusa can’t admit this is a genuine problem. 

RE: Brand new prusa mini: Z needs to adjust on every new print.

I've made a note of the cold and hot Z values. The cold value works reliably for the first print of the day. The difficulty is when I have to cancel the first print after a few minutes. Then I have to guess what the Z should be.

RE: Brand new prusa mini: Z needs to adjust on every new print.

Cool it before the print? Aim a fan on it for a while before the print, to cool down everything including metal parts? 🤔 

RE: Brand new prusa mini: Z needs to adjust on every new print.

@crawlerin

I've tried waiting until the hotend fan shuts off but that's not long enough. Most of my prints don't require a perfect first layer. As long as it sticks I can remove the elephant's foot. I really hope the solution from Prusa isn't to wait several minutes before starting every print. I feel the start up process already takes too long.