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

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JeremyN
(@jeremyn)
Eminent Member
RE: Brand new prusa mini: Z needs to adjust on every new print.

Just dropping in that I have the same issue. I need to check every first print of the day and adapt (lower) the Z-axis.
In my start gcode I do warm up the MINDA for 80 seconds.

Will drop a line to support, if we all contact them about this they might tackle it 🙂

Posted : 21/07/2020 8:03 am
Swishtail
(@swishtail)
Eminent Member
RE: Brand new prusa mini: Z needs to adjust on every new print.

I just ordered my Mini.... Hoping this gets addressed in the next 8 weeks.... 😮 

Posted : 21/07/2020 2:37 pm
stevethejedi
(@stevethejedi)
Eminent Member
RE: Brand new prusa mini: Z needs to adjust on every new print.

I'm also seeing this issue. The Z offset varies unpredictably within a range from -1.820 to -1.640, so you really have to monitor that first layer.

I haven't had a chance to do any controlled experimentation to see if I can find any of the patterns mentioned on this thread, I'll update if I find any.

Posted : 29/07/2020 5:26 pm
3Dprintedgr
(@3dprintedgr)
Estimable Member
RE: Brand new prusa mini: Z needs to adjust on every new print.

The biggest problem in my case is the difference when I change from PLA to PETG even the higher temperatures from the hotend have an impact on the sensor. It needs constant calibration which is frustrating. This problem exists since day 1 and I dont think Prusa will fix it any time soon. The only fix is to install a PINDA instead of a MINDA, I saw someone did it but the firmware needs to change (something that will void your warranty)

Original Prusa Mini + Smooth PEI
Prusa Slicer 2.2.0...
Posted : 29/07/2020 7:13 pm
Zane
 Zane
(@zane)
Eminent Member
RE: Brand new prusa mini: Z needs to adjust on every new print.

Just adding in my experience, exact same issue, z all over the shop nothing consistent. Raised the issue with support, got sent a new probe. Installed it, no difference.

A few weeks later a new support ticket, they advised me to preheat and see the results. It was like night and day, no more z issues for me as long as I preheat before starting a print. 

As with others, I just use gcode (found on the forums) to perform the preheat before every print.

G90 ; use absolute coordinates
M83 ; extruder relative mode
G28 ; home all
G1 X100 Y100 F4000
G1 Z1.5 F50 ; park position
M104 S170 ; set extruder temp for bed leveling
M140 S[first_layer_bed_temperature] ; set bed temp
M109 R170 ; wait for bed leveling temp
M190 S[first_layer_bed_temperature] ; wait for bed temp
G4 S180; wait 180 secs (x minutes) when heated up <--------------------
G28 ; home all without mesh bed level
G29 ; mesh bed leveling
M104 S[first_layer_temperature] ; set extruder temp
G92 E0.0
G1 Y-2.0 X179 F2400
G1 Z3 F720
M109 S[first_layer_temperature] ; wait for extruder temp

...
Posted : 29/07/2020 7:20 pm
Radmaster, 3Dprintedgr, stevethejedi and 2 people liked
Swishtail
(@swishtail)
Eminent Member
RE: Brand new prusa mini: Z needs to adjust on every new print.

@thomas-b13

Thank you for posting this.  I'm still waiting on my Mini to get here.  I'm assuming I'll need to figure out how to send this gcode with every print.  If this is a consistent issue across the fleet, seems like a firmware update should be made so this is done automatically.

Posted : 29/07/2020 7:54 pm
Texy
 Texy
(@texy)
Reputable Member
RE: Brand new prusa mini: Z needs to adjust on every new print.

@ben-kindt

You make the changes in prusaslicer and save it in a profile. Then it’s done every time you slice a model with that profile. 
Texy

Posted : 30/07/2020 5:33 am
herbert-1
(@herbert-1)
Active Member
RE: Brand new prusa mini: Z needs to adjust on every new print.

 

Hi all,

I implemented the preheat method as described above (made the respective G-Code part of my Prusa Mini profile) and was able to work without issues since then. But there are a few additional things that are likely contributing to me having no problems anymore.

I typically wait quite a bit after one print is done, because I mostly print PETG on the textured sheet, and the part comes of completely by itself if you have the patience to wait until the bed temperature has dropped below 40-50°C. Within these 5+ minutes, the hot-end and probe do of course cool down significantly, so it comes closer to the state that I have at the first print in the morning. Additionally I have adjusted my first layer to be squished to the bed quite strongly, i.e. my first layer is relatively thin. That ensures good first layer adhesion but gives a bit of an elephant foot to every part. (But that does not gain you a lot of margin for the z-height, maybe 50-100µm).

For a Printer that is advertised as a print farm work-horse, I find it disappointing anyway. (And I say this as a big fan of the overall Prusa eco system. I love my i3 Mk3S and I am a very active contributor to prusaprinters.org. But this issue simply sucks.)

 

Posted : 30/07/2020 5:27 pm
towlerg
(@towlerg)
Noble Member
RE: Brand new prusa mini: Z needs to adjust on every new print.

@herbert-1

"For a Printer that is advertised as a print farm work-horse" I checked and it does say that in the blurb. I think its a bit of a stretch myself, all that weight cantilevered seems like a machine for occasional printing rather tha 24/7.

Posted : 30/07/2020 5:42 pm
JeremyN
(@jeremyn)
Eminent Member
RE: Brand new prusa mini: Z needs to adjust on every new print.

@towlerg

I use it almost 24/7 and besides the Z-axis issue it lives up to that description. Just hope this gets fixed, cause it's not fun to have to retune the z-axis before every new print.

 

Besides this issue I have close to no other issues (most are related to this one, and another probably to the bad (slow-reading/writing, fast-heating) USB stick that is provided. If this gets fixed I will by more (or try my hand at a clone for the fun 🙂 )

Posted : 01/08/2020 9:01 am
towlerg
(@towlerg)
Noble Member
RE: Brand new prusa mini: Z needs to adjust on every new print.

@jeremy-naus

Impressive.

Posted : 01/08/2020 1:10 pm
stevethejedi
(@stevethejedi)
Eminent Member
RE: Brand new prusa mini: Z needs to adjust on every new print.

@thomas-b13

I've started using this g-code and it has mitigated the problem, thanks for sharing.

The issue is that all of that idle heating "burns" the filament in the nozzle, which eventually ends up on the print:

(As you can see I'm also dealing with some stringing issues...)

Posted : 01/08/2020 8:24 pm
JeremyN
(@jeremyn)
Eminent Member
RE: Brand new prusa mini: Z needs to adjust on every new print.

@stevethejedi

I first had 80 seconds in the gcode, solved it for the first couple of days. Now I've changed it to 180 seconds, hope that solves it 🙂
And I'm also having some stringing issue, but less severe. Still need to build my dry-box though

Posted : 01/08/2020 8:45 pm
JeremyN
(@jeremyn)
Eminent Member
RE: Brand new prusa mini: Z needs to adjust on every new print.
Posted by: @jeremy-naus

Just dropping in that I have the same issue. I need to check every first print of the day and adapt (lower) the Z-axis.
In my start gcode I do warm up the MINDA for 80 seconds.

Will drop a line to support, if we all contact them about this they might tackle it 🙂

Support go back to me they're sending me a new MINDA. Not sure that will fix it. But will try it anyway.

I advise everyone with this issue to contact support. If they keep getting the same issues over and over again, they might find a permanent fix 😀

Posted : 06/08/2020 7:16 am
PrusaTester2020
(@prusatester2020)
Trusted Member
RE: Brand new prusa mini: Z needs to adjust on every new print.

Just had an online chat with PRUSA support about the same issued I am also experiencing. They stated that this unreliable M.I.N.D.A. sensor is not a BUG but it’s a “feature by design” and is expected as a behavior. It was stated that the M.I.N.D.A. sensor was prone not only to printing heating but also to ambient temperature and the MINI was designed to have carefully manually checked every first layer and manually re-adjust Z axis for every print. WoW! 

The good news is that PRUSA is aware of the problem and was working on a solution and we should wait for (if it appears at all).

Posted : 31/08/2020 8:38 am
JeremyN
(@jeremyn)
Eminent Member
RE: Brand new prusa mini: Z needs to adjust on every new print.

@sth-udoma

Wow, first time they say it's working as designed.

The prusa Mini was always advertised as the perfect beginner printer. A beginner has zero clue about z-layer importance. A beginner will assume that, after getting it 'right' with the calibration, they are done (unless the switch sheets).
At least that was it for me as noob 🙂

Hope they fix it with either a PINDA (as there is an extra pin available on the motherboard) or in the start gcode.
With my start gcode fix it seems to be very consistent now.

Posted : 31/08/2020 8:52 am
Gordon W
(@gordon-w)
Reputable Member
RE: Brand new prusa mini: Z needs to adjust on every new print.

@sth-udoma

I think this may have been a case of the support person you were talking to being a bit confused or misunderstanding what someone had told him. If the situation was by design, i think the instructions with the printer would have directed users to check z height on every print and the issues on GitHub about this problem would have been closed as "working as designed".

Posted : 31/08/2020 8:57 am
PrusaTester2020
(@prusatester2020)
Trusted Member
RE: Brand new prusa mini: Z needs to adjust on every new print.

I said WOW in the chat and asked again a few times, but the support guy many times said it was not a bug but a feature of the MINI by design! He definitely recommended always to manually check the first layer and re-adjust it on the fly.

I also asked if during the print the M.I.N.D.A. sensor  changes its readings will it cause problem and the answer was that the change is not that significant.

Posted : 31/08/2020 9:04 am
PrusaTester2020
(@prusatester2020)
Trusted Member
RE: Brand new prusa mini: Z needs to adjust on every new print.
Posted by: @jeremy-naus

@sth-udoma

Wow, first time they say it's working as designed.

The prusa Mini was always advertised as the perfect beginner printer. A beginner has zero clue about z-layer importance. A beginner will assume that, after getting it 'right' with the calibration, they are done (unless the switch sheets).
At least that was it for me as noob 🙂

Hope they fix it with either a PINDA (as there is an extra pin available on the motherboard) or in the start gcode.
With my start gcode fix it seems to be very consistent now.

This pre-heating "start gcode" you execute it before each print OR you include in the begining of each gcode? Also after the pre-heating "start gcode" model is over (5 minutes) does the next model again measure the height of the heatbed or there is a setting in prusa mini to use the last measurements from the pre-heating "start gcode"!?!

Posted : 31/08/2020 12:44 pm
PrusaTester2020
(@prusatester2020)
Trusted Member
RE: Brand new prusa mini: Z needs to adjust on every new print.

I did a few tests: I printed a single layer 30x30 mm. square in the middle of the heat bed (printed  in diagonals). Printing time is at about 4 minutes using Prusa PLA filament at 215°C (print bed temperature set to 60°C). Room temperature at the beginning of the tests was 29°C according to the Prusa Mini display. I ran the test 4 times in a sequence without waiting in between.

  1. First run: Axis Z set to -0.650. The square is not adhesive and after the print is over it is easily separated from the heat bed. The result is a lot of separating strings. Not OK at all!
  2. Second run: Axis Z set to -0.650. The square is more adhesive and after the print is over it is not easily separated from the heat bed. The first half of the square again separates into strings. The second half started making a consistent area and is not separating into strings.
  3. Third run: Axis Z set to -0.650. The square is very adhesive and after the print is over it is difficult to separate it from the heat bed. The square is excellently printed and is a consistent square area.
  4. Forth run: Axis Z set to -0.650. The square is printed excellent again and again it’s difficult to separate it from the heat bed.

My conclusion is that MINDA probe changes its readings during the prints from Axis Z = -0.730 which would be OK for the first run, Axis Z = -0.680 ~ -0.650 which would be OK for the second and later runs. Clear evidence for this is the second run where the second half of the square is OK while the first one is not.

If I wait the Prusa Mini to completely cool down to room temperature and run a 5-minute 170°C pre-heat procedure at the beginning of the first run it is the same as if the first run is skipped. If I start again with a 10-minute 170°C  or longer pre-heat procedure at the beginning of the first run it is equal to the 5-minute 170°C pre-heat procedure. It proves that the pre-heat procedure partially solves the MINDA probe inconsistency and the MINDA needs a little more time at 215°C (for PLA) to be fully consistent.

But if after a long (more than 1 hour) print I immediately start a new print, then the Axis Z must be set to -0.500. If I leave it to -0.650 than it start scratching the surface. If I cool down the printer to room temperature then the Axis Z is OK again at -0.650. Also if I pause the print and wait until it cools down and then resume the work again the Axis Z must be set to -0.500 otherwise it is again too low.

 

My final procedure is:

  1. Wait the printer to cool down to room temperature or a few degrees higher.
  2. Print a single layer 30x30 mm. square with a 5-minute 170°C pre-heat code and check that the second half of the square is consistent (the first one is always separating).
  3. Wait a few seconds the temperature to drop to 170°C again.
  4. Start the final print with a 5-minute 170°C pre-heat code and check that the first layer is not scratching the surface.

All these pre-steps are just because the MINDA is not consistent 🙁

Posted : 09/09/2020 12:14 pm
Tracy liked
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