Live Z Adjust Constantly Decreasing  

Re: Live Z Adjust Constantly Decreasing

Hi

Mine needs to be readjusted after every print, either up or down. I have to reprint the Calibration print before every print. Sometimes it can be as much as 0.2mm difference in Z Adjust. This is even if I don't change filament. I am not moving the Z axis by hand or knocking it.

In this state, the printer is far harder to calibrate than my FlashForge and far less reliable. On that, I only had to check the calibration once a week with a piece of paper. The big selling point for me of this printer was the auto bed levelling and Z probe.

If the probe is two low, the bottom layer gets strange marks and patterns appearing in it. If it is too high, the print ends up lifting from the bed part way through. My success rate for prints is about 30% currently.

Sounds like mine.

Did yours function normally for a while, or has it always had this problem?

Mine started suddenly after I upgraded the firmware to 3.0.9. But I'm not sure if that is the cause. Others reported the problem with firmware 3.0.8.

I have not tried it repeatedly, but I think that printing the v2calibration before each print will not help you in this situation. The z-value will be all wrong again when you start the real print.

The way to get around this for me is to print a brim and adjust the live z adjust in the current print.

Now that I'm thinking about it, it would be smarter to print a second object at the same time, an object that just has one layer, but a large enough one to allow perfect fine-tuning of the z-adjust before the real print starts.

Any idea how to force Slic3r to start printing one of two objects first?

Re: Live Z Adjust Constantly Decreasing

Stephen, Daniel and Cyrille,

what exactly is the problem with your printers?

A few somewhat different scenarios have been described above, for example that the live-z-adjust needs to be changed in the same direction every time, or that it changes up or down, alternatingly, or maybe at random.

Mine is changing up or down. I'm still using 3.07 firmware, I've never had problems with this firmware except live Z adjust.

One thing to keep in mind: if you are using the last version of slic3r, you must not use your old gcodes. The first layer for the new version is 0.2mm (previous one was 0.15mm). If you calibrate your live Z adjust for the new slic3r, and try to print a gcode from the previous slic3r, your Z will be too high (0.05mm too high!!). I know this is another problem, and my problem with live Z adjust was before this new version with slic3r, but I was also confronted with this problem and wanted to warn other users.

Re: Live Z Adjust Constantly Decreasing

My first three prints came out fine, then it started to go wrong.

I am beginning to think this is my issue:
https://shop.prusa3d.com/forum/original-prusa-i3-mk2-f23/bed-adhesion-trouble-please-help--t2391.html

I have been cleaning the PEI sheet with 70% IPA. Could explain why it was fine at the start.

I've got some 99% IPA due tomorrow, so I will test it then. It prints perfectly if I use glue stick on the bed.

Re: Live Z Adjust Constantly Decreasing

My changing z-adjust value problem is gone! 😀 😀 😀

I'm not sure why, because I changed a number of things all at once, and not with the intent to fix the z-axis problem.

One possibility is that the PINDA "protector" causes this. I have today removed it after I noticed that it can break the PINDA probe by hitting the heat bed power connector plastic cover.

Does anyone have the 'Changing z-adjust-value-problem' who does not have a PINDA protector on the PINDA probe?

Anyway, I have taken the PINDA protector off.

I have also literally turned the printer upside-down, to get to the data cables underneath it. Then, I wrapped the cables in aluminium foil. That has solved another problem I had with cable extensions leading to SD card reader failure.

I also removed the 12ohm resistor (not stock, I had added it) from the heat-sink fan on the extruder, so the fan now runs at full speed while the printer is closed in in a plastic box.

I used the LCD control knob to move the X,Y and Z axes to all extreme positions, to check if the enclosure interferes with the printer. That's how I noticed that the PINDA 'Protector' is really more of a PINDA-breaker!

After all that mucking around, I ran the self test and the full X Y Z calibration and V2Calibration. It all went well.

When all that was done, I printed a calibration aid that I designed in OpenScad. I printed it 8 times in a row, including turning the printer off once, stopping the print, and pausing and then stopping the print. The live-z-adjust value did not need to be changed, I just played around with it between -0.325 and -0.375 to see the effects. Eventually I settled on -0.340 as the optimal setting.

Now I'm printing something I actually want to print, and I adjusted live z from -0.340 to -0.325 during the large 100mm Brim printing, because I saw some tell-tale signs of the nozzle being a bit too low.

So, I figure my problem is solved for now. Maybe someone else can figure out with certainty which of my actions (if any) have had this effect. 😉

Here is the OpenScad code for the test object, it is quite handy when you still have the 'Changing z adjust problem':

// Calibration square to be printed before main print object, to allow live-z-adjust.

cube ([75,20,0.2]);

Re: Live Z Adjust Constantly Decreasing

I just realised I changed even more that could have something to do with the absence of the problem now:

I modified the "End G Code" in Slic3r to:
G4 ; wait
M104 S0 ; turn off temperature
M140 S0 ; turn off heatbed
M107 ; turn off fan
G1 X125 Y200 Z200; home X axis and lift extruder for cleaning
M84 ; disable motors

This lifts the extruder to the top middle, easy to reach for cleaning, giving me time to remove dangling bits of filament when it starts to move for the pre-print calibration, and it keeps the PINDA probe away from the heat of the bed. Just in case you are one of those who think different temperatures of the PINDA probe are behind this problem.
Just reading my way through this thread which is related: http://shop.prusa3d.com/forum/improvements-f14/pinda-probe-live-z-calibration-z-offset-and-temper-t2048.html

Re: Live Z Adjust Constantly Decreasing

I tend to agree with the theory that raising the extruder before heating up the bed helps. At least my problems went away after i edited my end script. Definitely worth a try if you're having this flakey Z distance problem

Re: Live Z Adjust Constantly Decreasing

I had the Z adjust problem long before I put the protector on.

Re: Live Z Adjust Constantly Decreasing

Hey guys!

I have been having this problem for quite a while my self and it was driving me absolutely crazy. I realized that there was an actual issue and that I had just happened to have my probe set so close to the computed offset from my nozzle that I wasn't noticing it for a while. If you power cycle your printer and you are seeing any text message alerts then you are likely having the issue I am having. You will likely get one recommending you run the v2 calibration or that you need to run the xyz calibration for your printer. This is due to a bug in recent firmwares.

I have patched the firmware and tested it a fair bit on my own printer and it seems to be working great. I applied the patch to the current 3.0.9 firmware and have added a download link to the bottom of this post. If you have a few spare moments please check if you are getting a message on power up of your unit. If so please try my firmware. After flashing it please verify your z-height is set to 0!!! Because if you have been "adding" again and again the actually additional values will all be applied together and you will very likely run your nozzle into your bed. So set it to 0 and try to calibrate it again. Try printing something 2-3 times and verify that it has resolved the issue.

I hope this helps everyone else out as I imagine quite a few people have had this issue. I have submitted a pull request to get this patch into the official firmware as well. ( https://github.com/prusa3d/Prusa-Firmware/pull/32 )

Here is the firmware:
https://dl.dropboxusercontent.com/u/18990/3d%20Printing/Prusa%20Firmwares/Prusa_MK2_1_75mm_RAMBo13a-E3Dv6full.3.0.9.1-z-height-bug.hex?dl=1

Re: Live Z Adjust Constantly Decreasing

I have similar issues, after a perfect calibration, i can print few times without bothering Z, and suddenly i have to adjust it, lowering it, again and again.

For example, i just printed 4 identical parts, one after the other, after a V2 calibration:
- first one, with Live Z at 0.445, printed fine
- second one, unchanged, printed fine
- third one, Z is off, i have to lower it a lot, 1.135
- fourth one, Z is totally off, i have to set it to 2.325 (!)

I redo a V2 calibration (using last version of it), and ... after i adjusted it during the calibration, at the start of the next print, Z is totally off again.

So, something is wrong, the printed has no mechanical issue i'm aware of, and is able to do fine prints.

When i use Calibration > Auto Home, just after V2 calibration, sometimes it works fine, sometimes not at all (XY are ok, Z is off, nozzle too high).

I don't know if it is a firmware issue or a PINDA issue or whatever, but it is VERY annoying.

Current versions: MK2S, firmware 3.0.10 (latest)

Re: Live Z Adjust Constantly Decreasing

The problem has disappeared and my printer rarely requires and live-z-adjust now. It also stopped crashing into the print bed and not finding calibration points at random. I think it was related to PINDA probe height, at least it went away after I adjusted it during a rebuild.

I also adjusted the custom start code in Slic3r so that the extruder is away from the bed during heating up, even when the previous print finished unplanned.

Start code:
M115 U3.0.9 ; tell printer latest fw version
M83 ; extruder relative mode
G28 W ; home all without mesh bed level
G1 X100 Z200; move X axis off centre and lift extruder for cleaning
M104 S[first_layer_temperature] ; set extruder temp
M140 S[first_layer_bed_temperature] ; set bed temp
M190 S[first_layer_bed_temperature] ; wait for bed temp
M109 S[first_layer_temperature] ; wait for extruder temp
G28 W ; home all without mesh bed level
G80 ; mesh bed leveling
G1 Y-3.0 F1000.0 ; go outside pritn area
G1 X60.0 E9.0 F1000.0 ; intro line
G1 X100.0 E12.5 F1000.0 ; intro line

End code:
G4 ; wait
M104 S0 ; turn off temperature
M140 S0 ; turn off heatbed
M107 ; turn off fan
G1 X100 Y200 Z200; move X axis off centre and lift extruder for cleaning
M84 ; disable motors

Re: Live Z Adjust Constantly Decreasing

All inductive probes are affected by heat.
See Tom Sanladerer's sensor probe showdown here, .

Re: Live Z Adjust Constantly Decreasing

If you have the constantly changing z-adjustment problem, then consider if it may be related to switching SD cards.

JeffJordan wrote: 💡 so furthermore: if you got problems with an inconsistent sensitivity of your p.i.n.d.a. probe (which leads to different live z-adjustment levels) during operation of your printer: check the supply voltage for the probe ! if it varies only 0.05V (which is way inbetween the spec of the voltage regulator), your live z-adjustment level may vary about 100µm. this may be a problem especially when you "steal" some power of the 5V circuit (maybe to feed a raspberry...) or use an sd-card that requires significant more power than a standard one (as my mentioned toshiba flashair card).
http://shop.prusa3d.com/forum/improvements-f14/prusa-i3-mk2-my-way--t4047.html#p30108

Re: Live Z Adjust Constantly Decreasing

Hi everyone,

I have a MK2S from February, and I started having the same problem lately. After reading some messages in this thread I realised that I switched from Slic3r to Cura a couple weeks ago, and the problem started after a few prints with Cura generated gcode files.

In case anyone is having a similar issue, this is what I've found out: the Cura slicer levels the bed first and heats the extruder and bed after that. Slic3r did it the other way around. I suspect that messes up the PINDA probe measurements.

I modified the start and end gcode in the Cura printer profile this way.

Begin code:

1. Move the extruder high (150mm) so the PINDA probe won't be affected by the bed heat before the bed levelling.
2. Do things in the same order than Slic3r, and heat up extruder and bed before bed levelling.

Full modified code:
G21 ; set units to millimeters
G90 ; use absolute positioning
M82 ; absolute extrusion mode
G28 W ; home all without mesh bed level
G1 X0 Y0 Z150; home X axis and push Y forward and z axis up
M104 S{material_print_temperature} ; set extruder temp
M140 S{material_bed_temperature} ; set bed temp
M190 S{material_bed_temperature} ; wait for bed temp
M109 S{material_print_temperature} ; wait for extruder temp
G28 W ; home all without mesh bed level
G80 ; mesh bed leveling
G92 E0.0 ; reset extruder distance position
G1 Y-3.0 F1000.0 ; go outside print area
G1 X60.0 E9.0 F1000.0 ; intro line
G1 X100.0 E21.5 F1000.0 ; intro line
G92 E0.0 ; reset extruder distance position

End code:

1. Put the Z axis high so it won't be affected while the bed cools off.

Full modified code:
M104 S0 ; turn off extruder
M140 S0 ; turn off heatbed
M107 ; turn off fan
G1 X0 Y200 Z200; home X axis and push Y forward and x axis up
M84 ; disable motors

So far, it seems that the Z axis calibration issues have stopped.

Note: the end code is probably not necessary, but I like it that way because that forces the extruder to get out of the way when you print short items.

Re: Live Z Adjust Constantly Decreasing

Hi!

I'm so glad I've found this thread!

I also have troubles with my z adjustment. At first I thought it was because of me switching to different filaments (ABS/PETG/...) but now I mainly print PETG and still have to adjust my offset almost every print.
Over the last weeks I've found variations of +-0.075 resulting in offsets between 0.650 and 0.800.
In recent days printing only PETG these variations have come down to about +-0.040.

If the problem is the temperature of the probe itself it should help to get it down to ambient before bed calibration.
I'll give that a try and report back in a few days/weeks/...

B.t.w.: The title of this thread should be changed to something like "inconsistent z adjust" or "have to change z offset every print".
I almost didn't read this...

Re: Live Z Adjust Constantly Decreasing

Have you try this code?

M115 U3.0.9 ; tell printer latest fw version
M83 ; extruder relative mode
G28 W ; home all without mesh bed level
G80 ; mesh bed leveling
M104 S[first_layer_temperature] ; set extruder temp
M140 S[first_layer_bed_temperature] ; set bed temp
M190 S[first_layer_bed_temperature] ; wait for bed temp
M109 S[first_layer_temperature] ; wait for extruder temp
G1 Y-3.0 F1000.0 ; go outside pritn area
G1 X60.0 E9.0 F1000.0 ; intro line
G1 X100.0 E12.5 F1000.0 ; intro line

Re: Live Z Adjust Constantly Decreasing

Has anyone tried this in an enclosure? I had this live Z adjust issue with PLA prior to installing the MK2S in an enclosure for ABS (closed loop control set to 35C)

I never got to the bottom of this issue prior to the enclosure, but running the V2 calibration gcode prior to every print seemed to work, but now with the enclosure, it's so bad that I actually have to perform the live Z adjust during the print. If I perform it immediately before the print, then the nozzle will crash into the bed. This is driving me mad, so any help would be much appreciated.

Re: Live Z Adjust Constantly Decreasing

Has anyone tried this in an enclosure? I had this live Z adjust issue with PLA prior to installing the MK2S in an enclosure for ABS (closed loop control set to 35C)

I never got to the bottom of this issue prior to the enclosure, but running the V2 calibration gcode prior to every print seemed to work, but now with the enclosure, it's so bad that I actually have to perform the live Z adjust during the print. If I perform it immediately before the print, then the nozzle will crash into the bed. This is driving me mad, so any help would be much appreciated.

Ah, looks like this may have been resolved in the 3.0.11 firmware. Fingers crossed.

"Temperature calibration:

PINDA probe detection distance increases with temperature. This leads to need of adjusting live adjust Z values often, expecially when printing with different materials. Main contributor to PINDA temperature shift is heat received from heatbed. New temperature calibration was implemented to decrease this temperature dependency."

Re: Live Z Adjust Constantly Decreasing

I had the same issue of having to adjust the live Z value every time i retried a print. I did not power off or reset the printer in between each print.
With the first print i adjusted the live Z value to -0.600mm to get a good first layer.
With the second try of the same print, i had to set it to -1.200mm to get a good first layer.
With the third try of the same print i had to set the live Z adjust value to -1.800mm to get a good first layer.
Of course it is no coincidence that the difference between the Z values of the first, second and third print is -0,6mm (negative value means closer to the heated bed, so the extruder is moved down).
So it seems like the adjusted Z-value simply is not stored and has to be adjusted with the same relative amount with every new print.
To verify this, i checked the actual height of the Z axis with a dial gauge micrometer and found that the -0.6mm of the first print, the -1.200mm of the second print and the -1800 of the third print all resulted in the same height indicated on the dial gauge micrometer.
So i was fooled by a false Live Z adjust value that is shown on display but is not stored and is not representing the real Z offset that is used.
I noticed that when i reset/power off the printer, it showed a message telling me that i didn't adjust the distance between the bed and nozzle yet. This also indicated that the live Z adjustment was not stored at all.

While searching for conditions that have to be met, in order to save the Live Z value, i found the following URL :
http://help.prusa3d.com/mk2-firmware/live-z-adjust-not-storing
It says that the V2Calibration gcode HAS TO BE used in order to save the adjusted Live Z value.
I was not using the V2Calibration gcode when i was adjusting the Live Z value, so the Live Z adjust value was not stored and got me and probably lots of other users fooled and confused.

In the V2Calibration gcode, there are 2 special commands : G87 and G88 which probably have to do with saving the Live Z adjustment to EEPROM.
See : http://shop.prusa3d.com/forum/prusa-i3-kit-building-calibrating-first-print-main-f6/v2calibration-gcode-and-live-adjust-z--t3710.html

[EDIT] I'm using Firmware 3.0.11 and i'm not sure if older firmware behaves different.

Re: Live Z Adjust Constantly Decreasing

...
In the V2Calibration gcode, there are 2 special commands : G87 and G88 which probably have to do with saving the Live Z adjustment to EEPROM.
See : http://shop.prusa3d.com/forum/prusa-i3-kit-building-calibrating-first-print-main-f6/v2calibration-gcode-and-live-adjust-z--t3710.html
the G87 tells the printer that the calibration procedure was invoked, at least once, and that he has to store the z adjustment values from now on.
the G88 is a red herring.
i used the G87 in my 4th version of the little calibration surface as well (because you need to be very lucky to get the calibration right with the v2calibration.gcode).

Re: Live Z Adjust Constantly Decreasing

I'm having the exact same issue (Live Z adjust constantly needing adjustment), but only after upgrading the firmware to 3.0.11, and (so far) only after running multiple prints after one another without turning the printer off in between.

No idea what's causing this. It might have something to do with the 2 minute warmup not getting the PINDA probe as warm as being above the print surface for a longer time (i.e. during a print) does, so that might be messing with the distance readings. Of course, it could also just be a bug in the firmware, since it seems to increase in .3 mm intervals for me.

I've been thinking about downgrading the firmware, but I don't want to lose PID calibration, which keeps nozzle temperature really stable.