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First layer problem (MINDA Probe broken?)  

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hoops.frederic
(@hoops-frederic)
Active Member
First layer problem (MINDA Probe broken?)

Hey community,

I have a problem with my Pusa Mini and its first layer.

So first of all I did the first layer calibration with the z-axis adjustment, which worked very well. First layer looked great. (Sticked well and had no gaps)

But for some reasons on the first print of the day or when the printer was offline a long time, so when its "cool", the first layer looks horrible.

If I start the exact same gcode right after that first print, the first layer looks perfect, so its not my slicver settings or something.

Also when I preheat for like 5 minutes, the first layer looks good as well, so I guess its definitely a temperature thing.

But tbh I cant imagine ehat its necessary to preheat before every single print..I also cant find anything about that in the inetrnet, so I guess theres an issue with my MINDA probe (does bed levelling before every print)

 

I installed Pronterface to do some tests. You can see the results attached. I did bed levelling with a different time of preheating (warmup in the diagram). The 2 diagrams on the left side show the results of a /very) short warmup, while the two on the right side show the results of a preheat of like 5 minutes.

Both trys with the very short warmup have a bad first layer while the other ones have an almost perfect first layer, with one of the long warmups having a slightly squished one (as described in the picture). 

The other 3 pictures show the difference of the mesh bed leveling output of the perfect layer minus the other tests (see the title of each picture for further description). You can see that both bad first layer (short warmup) tests differ from the perfect layer in the same way, while the squished one differs substantially less and also differs in the other direction, which could explain the squished result.

Could this behaviour be explained by a bad M.I.N.D.A. probe? Any way of fixing the issue? I certainly don't want to preheat my printer everytime for about 5 minutes, as it's not the expected behaviour. A possible workaround would be to calibrate the meshbed only e.g. once a week, while I preheat the printbed for a longer period for said calibration, not sure if that's possible. However I wouldn't be satisfied by that workaround in the long run and therefore would ask for prusa to help me out here.

 

Thanks in advance,

Frederic

 

This topic was modified 2 years ago 2 times by hoops.frederic
Posted : 29/04/2020 4:44 pm
hoops.frederic
(@hoops-frederic)
Active Member
Topic starter answered:
RE: First layer problem (MINDA Probe broken?)

https://imgur.com/a/Lt3khKK

Here are the images uncut and in better resolution

This post was modified 2 years ago 2 times by hoops.frederic
Posted : 29/04/2020 4:52 pm
bobc
 bobc
(@bobc)
Reputable Member
RE: First layer problem (MINDA Probe broken?)

Your analysis matches my experience. A short or no warmup gives a Z too high, a long warmup is lower. I have a 1 minute wait in my GCode, if the first layer is not good I restart and then it is usually ok.

For back to back prints, I wait until the extruder fan has gone off, before starting the next print.

I guess there is variation between MINDA probes, possibly a new one will behave differently. I think Prusa know how to fix it, that is to put a temperature sensor in the probe, but they decided not to do that on the Mini. It's a budget printer, ya know 😉

Posted : 30/04/2020 12:04 pm
avrcore
(@avrcore)
Active Member
RE: First layer problem (MINDA Probe broken?)
Posted by: @bobcousins

Your analysis matches my experience. A short or no warmup gives a Z too high, a long warmup is lower. I have a 1 minute wait in my GCode, if the first layer is not good I restart and then it is usually ok.

For back to back prints, I wait until the extruder fan has gone off, before starting the next print.

I guess there is variation between MINDA probes, possibly a new one will behave differently. I think Prusa know how to fix it, that is to put a temperature sensor in the probe, but they decided not to do that on the Mini. It's a budget printer, ya know 😉

In what line did you place the wait gcode command?

 

G90 ; use absolute coordinates
M83 ; extruder relative mode
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
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

; intro line
G1 X170 F1000
G1 Z0.2 F720
G1 X110.0 E8.0 F900
G1 X40.0 E10.0 F700
G92 E0.0

M221 S95 ; set flow

Posted : 02/05/2020 2:12 am
DRKMSTR
(@drkmstr)
Trusted Member
RE: First layer problem (MINDA Probe broken?)

It's temperature drift due to a probe that doesn't have a temperature sensor. 

All mini users have this problem. If you haven't experienced it yet, try printing with a different material.

Try preheating the bed after homing the printer, then printing. (Oh no, it's too low now) Try doing first layer calibration from a cold printer, then doing it again immediately with a warm printer, totally different results.

The board can support a probe with a temperature sensor, but they refuse to offer the firmware support to do so. I'll gladly pay the $20 to get a probe to make the mini work, but as of yet it is not reliable enough for remote printing.

Posted : 02/05/2020 2:37 am
marcel.mayer
(@marcel-mayer)
Active Member
RE: First layer problem (MINDA Probe broken?)

Please see here:
https://forum.prusaprinters.org/forum/hardware-firmware-and-software-help/analysed-problems-with-minda-probe/

Posted : 21/09/2020 7:08 pm
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