Unable to print PLA

wouldstain

@deckingman The issue only occurs when printing PLA. PETG prints reliably.
The grinding has become a non-issue since the addition of the MFM.

What is vexing about this is that there is no actual blockage. I am able to immediately issue a manual extrude command following a stop with no issue. To ensure there was no small / partial blockage, I replaced the nozzle, throat and PTFE tube between the extruder and hotend.

I am not holding filament at print temp for extended periods. This occurs randomly during any prints with PLA, and again, I can manually extrude immediately after the MFM triggers a pause due to lack of filament movement.

Additionally, I have attempted to print gcode that I had sliced and printed prior to the onset of this issue. These models will no longer print but the retraction settings are baked into the gcode.

I do not disagree about the difference in material properties being a factor, but I am baffled as to what else I can do to isolate the issue, although I have not yet tried replacing the heat break fan.

I will order a replacement heat break fan and give that a try, but otherwise, I am not sure what else is left.

Thank you!

wouldstain

@petrkroupa I'm using a 0.9 ° LDO motor. I'm looking at the packaging for the extruder and it does not indicate the gear ratio but looking at the website I believe it is 3:1.

As far as the settings go, what I'm using closely follows a widely used starter Railcore config.g. Additionally, the person who generated that original config has a very similar hardware setup (same extruder and extruder motor) so I would hesitate to start making changes there as I know his is working with these same settings.

I have tried printing with 0 retraction distance and 0 pressure advance as well as many combinations of both.

Thank you for responding! I really appreciate the input!

wouldstain

@o_lampe

Thank you! Corrected S value for M574!

As far as it connecting to PWM1, the connections are correct per
the Railcore build guide here.

achrn

This doesn't really fit all your symptoms, but what is the ambient temperature - that is, temperature of the air around the extruder?

I have a printer with direct drive extruder inside a fairly insulated enclosure, and PLA doesn't like it when the air in the enclosure gets too hot. The extruder is hobbed drive direct on the stepper shaft. If the air in the enclosure gets too warm, and the extruder gets hot, the stepper skips steps as if filamnet is jammed.

I fixed mine by gluing (with conductive epoxy) heat-sinks on the sides of the extruder stepper and arranging a fan and shroud to blow through the heatsink pins, plus opening the doors of the enclosure if it gets too hot.

I felt possibly the surface of the filament was softening enough to not feed nicely. I admit, it doesn't sound likely, but one hot summer I had all these filament feed problems, and cooling the stepper resolved them, so...

I'm not at all convinced this fits your case, because in a BMG the filament drive won't be getting heat conducted from the stepper, but it's another variable to explore...

wouldstain

@rjenkinsgb

I do not think there are any wiring problems but I was planning on doing a rewire to switch to a drag chain configuration in the near future, so I will be re-seating / reconnecting everything.

I had not considered the power supply as a possible source of trouble as PETG prints consistently. I do not have another 24V power supply to to test with, however I would expect that if there was any dip in voltage output I would see a dimming in the lighting kit.

I do have a fluke meter with data logging capabilities if you happen to have some suggestions on what to look for.

Thank you for your input! I would love to get this put to rest!

deckingman

@wouldstain said in Unable to print PLA:

................. What is vexing about this is that there is no actual blockage.

Well that depends on how you define blockage. The fact that you've had the extruder grinding away at the filament indicates that there must be some sort of restriction. As I tried to explain, PLA has a very low glass transition temperature of about 60 deg C. So, if you get heat creep up through the filament, or if you pull pull too much filament out when you retract, then you can end up with filament that is above the glass transition temperature, inside the heat break. When you then "unretract" the filament, the pressure from the extruder will the cause this softened filament to swell and bulge out sideways rather than travel forward, and so it (partially) blocks the heat break - or more precisely, it causes a restriction. I'm even more convinced that this is what is happening because you say that you can then manually extrude. Which indicates that the swollen filament inside the heat break has either cooled and hardened, or it has softened further and thus become less viscous.

I do not disagree about the difference in material properties being a factor, but I am baffled as to what else I can do to isolate the issue, although I have not yet tried replacing the heat break fan.

I will order a replacement heat break fan and give that a try, but otherwise, I am not sure what else is left.

Before you do that, reduce or disable retraction and see what happens. The print might have blobs and be stringy but it will prove a point one way or another. Ideally, look at using firmware retraction (G10/G11). This is much better because it enables you to tune it "on the fly" - both distance and speed.

EDIT. By they way, I've spent the last two years designing and building prototype hot ends, and before that spent a few years "taming" multi-input mixing hot ends. I've seen exactly the sort of thing you describe many times.

wouldstain

@deckingman Just tried multiple test prints with zero retraction

First one:

MFM stopped the job with the following error:
"Extruder 0 reported 'tooLittleMovement'"

Output from M591 D0:

Duet3D rotating magnet filament monitor v3 on pin e0stop, enabled, sensitivity 26.50mm/rev, allow 1% to 200%, check every 3.0mm, version 3, mag 130 agc 74, measured sensitivity 26.48mm/rev, min 0% max 105% over 606.9mm

If not for the MFM, this is where it would the extruder would start grinding away at the filament.

Repeated test with similiar results with temperatures ranging from 190C to 230C.

Also:
m572
Extruder pressure advance: 0.000

PetrKroupa

@wouldstain - Firts your AGC value is too low.

In my opinion, a 0.9 stepper on a geared extruder doesn't make sense. 0.9 always has less torque and less speed at the same voltage. Maybe it's one of the problems you have. PLA is relatively dense and is more difficult for the extruder to extrude.

o_lampe

@wouldstain said in Unable to print PLA:

As far as it connecting to PWM1, the connections are correct per
the Railcore build guide here.

Do you use an external 5V supply for the Duex? Otherwise the BLTouch servo connection is shady

deckingman

@wouldstain said in Unable to print PLA:

@deckingman Just tried multiple test prints with zero retraction ..................

If not for the MFM, this is where it would the extruder would start grinding away at the filament.

Repeated test with similiar results with temperatures ranging from 190C to 230C.

But you can reliably print PET-G yes? Have you tried recently? It would be important to know for sure if this is related only to PLA or if some other factor has crept in between you trying PET-G and then switching to PLA.

T3P3Tony

@wouldstain said in Unable to print PLA:

any dip in voltage output

You can check this by sending M122 - Vin voltage is monitored by the Duet.

@petrkroupa said in Unable to print PLA:

@wouldstain - Firts your AGC value is too low.

AGC can be too high (over 110 or so) but not really too low in our MFM design. A lower value indicates the magnetic field is being sensed more strongly, so better. (it is presumably possible to have a huge magnet and have a different problem but that does not apply here.

@wouldstain
can you try the following test:

Slice a file for PETG, that previously did not work for PLA, preferably with no retractions.
Confirm it prints correctly with PETG
manually edit just the temperature setting at the beginning of the file to be appropriate for PLA.
reprint it with PLA.

wouldstain

@t3p3tony

After @deckingman's replies, I took a closer look at the heat break fan and realized it could be seated a bit lower
on the heat sink and moved it. Sadly it did not change the results.

Tried another PLA job @200 and 215 with same result. M122 Voltage looks normal.

M122.txt

I will follow up with a PETG and PLA with manually adjusted temp and post results.

wouldstain

@o_lampe Duex has it's own positive lug on 24V power supply. Negative is chained with main board per build instructions here+Wiring+the+Electronics/16?lang=en).

wouldstain

@petrkroupa The extruder and motor combination is common configuration for Railcore.
AFAIK I'm the only one having this issue so it's something specific to my components, physical installation, or slicing. However, the slicing has been tested by others already in previous thread and as I've mentioned, this has not always been a problem.

Aside from cleaning the hotend, extruder and swapping out the nozzle, throat and bowden tubes, the rest of the configuration is relatively unchanged from initial build when it was working.

fcwilt

@wouldstain

What kind of PLA are you trying to print?

Certain types of PLA require little or nor retraction.

Frederick

wouldstain

@fcwilt Ive tried several brands of PLA, all with the same result.

wouldstain

@t3p3tony PETG printed as well as you would expect with no retraction or pressure advance... ugly corners and some stringing across axis markers on XYZ calibration cube.

PLA wont even finish the starting nozzle wipe at the moment. Tried three times.

Only differences in setup:

PETG:
Layer 1 Print temp: 235C
Layers > 1 Print temp: 230C
Z offset: -.15

PLA:
Print Temp: 220C
Z offset: 0

This is a new error:
M120 M83 G1 E100 F300 M121
Error: G0/G1: insufficient axes homed

Also found this in the console from earlier:
M290 R1 Z-0.05
Error: M290: insufficient axes homed
Error: M290: insufficient axes homed

Again, all axis are homed and machine starts up PETG jobs normally.
Not sure if this is related or not but I don't imagine I should be seeing these errors.

Both gcode files attached.

no_retract_PLA_220_xyzCalibration_cube.gcode

no_retract_PETG_230_xyzCalibration_cube.gcode

wouldstain

@T3P3Tony One other thing I just remembered, not that it should make a difference... When I replaced the heatbreak, I used Boron Nitride paste rather than white thermal grease (had some handy at the time!) but I don't think this is the issue as the problem started prior to replacement.

To eliminate this as a variable, I have ordered some white thermal grease of the same composition as that provided by E3D in their hotend kits. It should be here tomorrow so I will pull apart the hotend, clean it and put in another heatbreak with white thermal grease. That should return it to as absolutely close to its original configuration as I can get it.

@deckingman's responses re: glass transition point have me going over everything in my head that could impact temperature at the heatbreak.

T3P3Tony

@wouldstain said in Unable to print PLA:

M122.txt
Supply voltage: min 23.9, current 24.1, max 24.3, under voltage events: 0, over voltage events: 0, power good: yes

That shows that between the last M122 and that M122 (or power up) you have not had any power issues with VIN.

@wouldstain said in Unable to print PLA:

M120 M83 G1 E100 F300 M121
Error: G0/G1: insufficient axes homed
Also found this in the console from earlier:
M290 R1 Z-0.05
Error: M290: insufficient axes homed
Error: M290: insufficient axes homed

that looks like you tried to babystep without the axis homed.

When you say it wont print past the pruge line, do you mean the filament monitor errors at that point?

wouldstain

@t3p3tony

that looks like you tried to babystep without the axis homed.

I did indeed! one less thing to worry about!

When you say it wont print past the pruge line, do you mean the filament monitor errors at that point?

Correct. In fact, I just took a look at the bed and the purge line looked to be about half of normal length when it paused.

Extruder 0 reported 'tooLittleMovement'

m591 d0

Duet3D rotating magnet filament monitor v3 on pin e0stop, enabled, sensitivity 26.50mm/rev, allow 1% to 200%, check every 3.0mm, version 3, mag 131 agc >>75, measured sensitivity 1079.51mm/rev, min -31% max 133% over 16.9mm

Even though I've never set a firmware retraction value or used G10/G11, I did take a look at M207 just to see if there was anything and found this:

Tool 0 retract/reprime: length 2.00/2.00mm, speed 16.7/16.7mm/sec, Z hop 0.00mm

dont know if that matters w/o G10/G11 calls but it is there.