MK3S sticking/z-offset/extrusion problems  

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david.r45
(@david-r45)
New Member

Hello, a few months ago, I have upgraded my printer from MK3->MK3S and so far, I have not been able to get the print quality back to where it was pre-upgrade. I do not know what the problem is, but I will try to describe symptoms and maybe the problem will be clear to some of you. In order to simplify an already complicated problem, I will only talk about using a 1.5 year old smooth PEI sheet and a variety of different PLA colors/manufacturers.

1) The first layer calibration procedure is inconsistent. I was used to getting a stable zig-zag line of filament, but now the line is often broken in many places, sometimes replaced only with a few dots, and sometimes full as it should be. Especially in the 90 degree turns, there is often no material deposited and only a string "cutting the corner short". Changing z-offset can help a bit, but the first layer calibration is never perfect. What is more, the little "carpet" at the end of the calibration can look terrible in one run and then reasonably OK in another run with the same exact z-offset.

After trying several things, what helped was to stop treating the PEI sheet with IPA before every print. Suprisingly (to me), the first layer calibration sticks well and looks OK if I run it after having already ran it a few times without cleaning. So after cleaning the sheet with IPA before every print for 1.5 years, I now don't clean the sheet on purpose and it works better. However, I sense there might be a problem causing all this, so I'd love to hear some insights. (Also, if larger prints start unsticking now, I cannot go to my previous "clean with IPA" fix, so I am not sure what to do in that case.)

2) While attempting to solve inconsistent extrusion, I played with the tension in the extruder and arrived at a satisfactory point, where the extrusion was more or less good. However, twice already (with the same filament every time), the extruder motor started skipping and after unloading the filament, I noticed that the filament broke just below the bondtech gears and was slightly bent away from the proper "line" which made it get stuck and prevented more filament to enter the nozzle.

Some frustrating times with pliers allowed me to take the filament out and reload, but I am worried it is going to happen again. What could be the cause? I have had many successful prints with this filament and printer in the past without any issues.

Thank you!

Posted : 18/09/2019 10:16 am
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(@-2)
Illustrious Member

Try using a temperature stabilization method.   

Heat the bed, preheat the nozzle, let the PINDA warm to a defined higher temperature, perform mesh level, final heat the nozzle, print.

The PINDA can be pretty useless over a wide temperature range.  So run to run mesh levels give wildly different results (I've personally experienced this).  I now wait for the PINDA to reach 40c - and this has added consistency to my layer 1 quality.

M115 U3.7.1 ; tell printer latest fw version
G90 ; use absolute coordinates
M83 ; extruder relative mode

; preheat things to a low temp, , get nozzle plastic mushy before driving into the bed with G28
M140 S[first_layer_bed_temperature] ; set bed temp
M109 S180 ; wait for extruder temp
G28 W ; home all without mesh bed level
M190 S[first_layer_bed_temperature] ; set & wait for bed temp

; soak PINDA then level
G0 X50 Y50 Z1 F3000; this is a good PINDA heating position
M860 S40 ; wait until PINDA is >= 40C
G80 N7 R5; mesh bed leveling

; heat to extrude temp
G0 X0 Y-3.0 Z10 F3000; this is a good nozzle heating position
M109 S[first_layer_temperature] ; set & wait extruder temp

; purge
G1 Y-3.0 Z0.15 F1000.0 ; go outside print area
G92 E0.0
G1 X60.0 E9.0 F1000.0 ; intro line
G1 X100.0 E12.5 F1000.0 ; intro line
G92 E0.0
M221 S{if layer_height<0.075}100{else}95{endif}


This post was modified 2 years ago 2 times by --
It is always wise to get more than one opinion... as for trusting Prusa? No way man....
Posted : 18/09/2019 6:33 pm
Nigel liked
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(@-2)
Illustrious Member

And another point worth mentioning: the initial Live-Z cal using the firmware is required; but once that's done, using a large solid part for adjustment is better.  It also allows time to make adjustments and see real world results.

Cal Circles

It is always wise to get more than one opinion... as for trusting Prusa? No way man....
Posted : 18/09/2019 6:49 pm
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