Wiper Pad Alternatives

A forum dedicated to the stock LulzBot Mini 3D Printer
IDEngineer
Posts: 43
Joined: Sun Feb 05, 2017 2:36 pm

Re: Wiper Pad Alternatives

Post by IDEngineer » Mon Nov 19, 2018 11:26 am

kcchen_00 wrote:
Sun Nov 18, 2018 6:40 pm
Use a skirt. It will prime the nozzle and the "glob" will be deposited on the skirt rather than your print.
I do use a skirt. It's the default in the Lulzbot version of Cura. What happens is the glob of filament flows down to the print bed as the nozzle lowers to it in preparation for printing, the nozzle squishes into the glob below it, and then as the skirt starts the glob is dragged around by the nozzle and adheres to the first layer - ripping it right back off the print bed.

The problem is the glob that happens right at the start. Sometimes I can grab most of it with tweezers but there's always some left stuck on the sides of the nozzle, and then it's a crap shoot whether it sticks to the skirt or print at some point later.

monsteroyd
Posts: 33
Joined: Fri Jul 06, 2018 3:30 pm

Re: Wiper Pad Alternatives

Post by monsteroyd » Mon Nov 19, 2018 11:38 am

IDEngineer wrote:
Mon Nov 19, 2018 11:26 am
kcchen_00 wrote:
Sun Nov 18, 2018 6:40 pm
Use a skirt. It will prime the nozzle and the "glob" will be deposited on the skirt rather than your print.
I do use a skirt. It's the default in the Lulzbot version of Cura. What happens is the glob of filament flows down to the print bed as the nozzle lowers to it in preparation for printing, the nozzle squishes into the glob below it, and then as the skirt starts the glob is dragged around by the nozzle and adheres to the first layer - ripping it right back off the print bed.

The problem is the glob that happens right at the start. Sometimes I can grab most of it with tweezers but there's always some left stuck on the sides of the nozzle, and then it's a crap shoot whether it sticks to the skirt or print at some point later.
Wow are you sure your nozzle doesn't have a problem. Mine never globs like that. If you've tried everything else, maybe a new nozzle?

Monty
Lulzbot Mini 2

IDEngineer
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Re: Wiper Pad Alternatives

Post by IDEngineer » Mon Nov 19, 2018 2:45 pm

This IS a new nozzle. Brand new Micro Swiss 3mm/0.5mm nozzle. Literally installed it a couple of days ago, thinking it might be the cause. It's obviously not.

Also, this dribbling issue is across multiple types and colors of filament. And temperatures. I've tried everything I can think of, including the brand new Micro Swiss nozzle, and nothing helps.

monsteroyd
Posts: 33
Joined: Fri Jul 06, 2018 3:30 pm

Re: Wiper Pad Alternatives

Post by monsteroyd » Mon Nov 19, 2018 2:50 pm

That's weird. When I extrude I get a line of plastic that goes down to the bed. It may start to loop back up to the nozzle once that line cools and hits the bed, but that is it.

It did this BEFORE the new nozzle too?

I would contact Lulzbot support to see what to do. You're beyond my meager experience. Everything just works for me (hope I didn't jinx myself).

Monty
Lulzbot Mini 2

IDEngineer
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Re: Wiper Pad Alternatives

Post by IDEngineer » Mon Nov 19, 2018 4:52 pm

monsteroyd wrote:
Mon Nov 19, 2018 2:50 pm
It did this BEFORE the new nozzle too?
Yes.
I would contact Lulzbot support to see what to do.
So far they've had me:

1) buy two new printhead fans

2) buy a larger printhead fan and convert the style used on my printhead to this new style

3) buy a brand new print bed, but fail to tell me that the new one ALSO required a new heater pad

4) buy a new heater pad after the new print bed showed up, or else the new print bed was a complete waste of money

...and none of this made any difference in the problems this Mini is having.

I bought the new nozzle on my own, because at least that seemed logically like it might have an effect on the dribbling/oozing problem. No luck there either.

I've spent more on replacement parts than it would have cost to buy a brand new 3D printer from many sources. Imagine how happy I am about that. :evil: :evil: :evil:

ScottW
Posts: 452
Joined: Thu Dec 10, 2015 1:00 pm

Re: Wiper Pad Alternatives

Post by ScottW » Mon Nov 19, 2018 7:19 pm

IDEngineer wrote:
Mon Nov 19, 2018 4:52 pm
So far they've had me:
1) buy two new printhead fans
2) buy a larger printhead fan and convert the style used on my printhead to this new style
3) buy a brand new print bed, but fail to tell me that the new one ALSO required a new heater pad
4) buy a new heater pad after the new print bed showed up, or else the new print bed was a complete waste of money
...and none of this made any difference in the problems this Mini is having.
I bought the new nozzle on my own, because at least that seemed logically like it might have an effect on the dribbling/oozing problem. No luck there either.
I've spent more on replacement parts than it would have cost to buy a brand new 3D printer from many sources. Imagine how happy I am about that. :evil: :evil: :evil:
Odd problem.... Most minis typically have a little of the opposite problem; i.e., not primed sufficiently. What I usually saw was that when the skirt started, not enough material was in the nozzle so the first couple inches wouldn't "stick" and sometimes ended up getting dragged into print area. I actually added MORE priming action to alleviate that.

I changed the start Gcode... After warming to print temperature at left-front corner, I have it move semi-close (higher than normal layer) to the bed and then extrude a "blob" while moving upward (to avoid having the blob stick to the nozzle). That primes the nozzle and sticks the "blob" to the bed, then it moves "up and away" from the blob. The skirt code (from slicer) then starts. This same technique *might* fix your problem, since any "ooze" would be captured as part of the blob at the corner of the bed.

Only other thought... Wet filament will cause excessive oozing during heatup. Tell-tale sign is the filament gradually oozing out and changing directions rather than just oozing straight downward. You could try "baking" some filament (45C for pla, 60C for ABS, 65C for PETG or Nylons) and see if it changes the behavior. 1-2 hours is sufficent for most filament, but nylons may take 4-6 hours.

I'll include my start/end gcode in case you want to see how I manage the priming "blob" and end-job retraction. Some explanatory notes:
  • These scripts are from Simplify3d; the temperature variable names for extruder/bed are different than Cura uses.
  • I use the dual-wiper thing mentioned earlier in this thread, hence the extra wiping commands.
  • I use custom firmware and have made some adjustments to my bed XY origin points, so your XY position for corner of bed and wiper might be slightly different.
  • These scripts are for ABS, adjust wipe/probe and bed cooldown temperatures accordingly for other materials.
  • The end script leaves the bed at center rather than moving forward; this is because I use Octoprint and it takes a photo to mail at print completion and I want the bed centered for the photo.
  • These scripts have a "move away from endstops" after all G28 commands. This was required for certain versions of firmware, but similar movements were added internally to G28 in one of the 1.1.9.xx versions and are no longer needed (but won't hurt).


START SCRIPT

Code: Select all

;FOR LULZBOT MINI AEROSTRUDER
G26		; clear potential probe-fail condition
G21		; metric values
G90		; absolute positioning
M82		; set extruder to absolute mode
M107		; start with the fan off
G92 E0		; set extruder position to 0
M140 S[bed0_temperature]	; begin bed heating
G28 		; home all axes
G0 X-2 Y189 Z158 F200 	; move away from endstops
M109 S155		; set and wait for RETRACT TEMP (ABS=155)
G1 E-15 F150		; suck up 15mm of filament
M109 R170		; set and wait for WIPE+PROBE TEMP (ABS=170)
G1 X42 Y173 F11520	; move nozzle over wiper pad
G1 Z0.5 F1200		; push nozzle into wiper
G1 X42 Y173 Z0.5 F4000	; wiping
G1 X52 Y171 Z0.5 F4000	; wiping
G1 X42 Y173 Z1 F4000	; wiping
G1 X52 Y171 F4000	; wiping
G1 X42 Y173 F4000	; wiping
G1 X52 Y171 F4000	; wiping
G1 X42 Y173 F4000	; wiping
G1 X52 Y171 F4000	; wiping
G1 X57 Y173 F4000	; wiping
G1 X77 Y171 F4000	; wiping
G1 X57 Y173 F4000	; wiping
G1 X77 Y171 F4000	; wiping
G1 X57 Y173 F4000	; wiping
G1 X87 Y171 F4000	; wiping
G1 X77 Y173 F4000	; wiping
G1 X97 Y171 F4000	; wiping
G1 X77 Y173 F4000	; wiping
G1 X97 Y171 F4000	; wiping
G1 X77 Y173 F4000	; wiping
G1 X97 Y171 F4000	; wiping
G1 X107 Y173 F4000	; wiping
G1 X97 Y171 F4000	; wiping
G1 X107 Y173 F4000	; wiping
G1 X97 Y171 F4000	; wiping
G1 X107 Y173 F4000	; wiping
G1 X112 Y171 Z0.5 F1000	; wiping
G1 Z5		; -- raise z prepare for move to secondary wiper
G1 X105 Y181		; -- right end of secondary wiper
G1 Z1		; -- Move down to pad
G1 X49 Y181.5 F4000	; -- wipe off lint
G1 X105 Y181 Z0.5 F4000	; -- wipe off lint and go deeper
G1 X49 Y181.5 Z2 F4000	; -- wipe off lint while moving up and away
G1 Z10		; raise extruder	
G28 X Y 		; home X and Y
G0 X-2 Y189 F200 	; move away from endstops
M204 S300		; set probing acceleration
M400 		; wait for clear buffer
G29		; start auto-leveling sequence
M204 S2000		; restore standard acceleration
M104 S[extruder0_temperature]	; begin heating extruder to print temp
G28 X		; home X to fix any coordinate shift during G29
G0 X-2		; - untrigger
G28 Y		; home Y to fix any coordinate shift during G29
G0 Y189		; - untrigger
G1 X-2 Y6 Z8 F3500	; move to warmup position
M400		; wait for moves to finish
M109 S[extruder0_temperature]	; wait for extruder temp
M190 S[bed0_temperature]	; wait for bed temp if needed
G1 Z0.6 E0 F125	; - extrude filament back into nozzle and move close to bed
G1 Z1.8 E6 F125	; - extrude a blob to prime nozzle
G1 E5.5 F250		; - small retract
G1 X12 Y12 Z5 F5000	; - move up and away from blob
G92 E0		; - reset current extruder position to 0
END SCRIPT

Code: Select all

G91		; relative
G0 E-5 F900		; retract
G0 Z3 F480		; move away from part
G90		; absolute
G92 E0		; set extruder 0
M104 S0		; hotend off
M140 S0		; bed heater off 
M107		; fans off
G1 X90 Y5 Z158 F10000	; move to cooling position 
G0 E4 F200		; re-prime most of retraction
M190 R50		; Set and wait for PEI BED REMOVAL TEMP (ABS=50)
G1 Y80 F1000		; move to middle for end-of-print photo
M84

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mwester
Posts: 103
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Re: Wiper Pad Alternatives

Post by mwester » Mon Nov 19, 2018 7:33 pm

I have to wonder if you're not suffering from overtemp.

The retraction for the mini is perfectly normal -- 30mm is a bit over an inch (that's also what the two minis I've had have done) and that pulls the filament almost completely out of the hot-end. So, logically, there shouldn't be any filament inside the hot metal area to melt and ooze out in the first place!

So, I'm wondering if your filament is simply too hot, so that the retraction just stretches the filament, leaving some of it down in the hot-end, and the overly-hot hot-end melts what's there and drips it onto the bed.

Two possibilities come to mind: One is that yu've replaced the fan that blows on the heat-sink, you stated above -- double-check that fan to make sure that it's pushing air through that head-sink. Another possibility is that you may simply have a bad thermister -- use an IR thermometer and check that the nozzle temp matches what the firmware is reading.

Regardless, the above doesn't address the lack of "stickiness" of the filament to the bed. Almost sounds as if there's something (like a layer of oil) on the PEI surface. As a test, put down a layer of blue tape, being careful not the overlap it. You'll need to adjust your Z-Offset (again) to compensate. But that should give you a clean, known-good surface to get the filament to adhere.

None of the above tests should sink a lot more money into that thing; sounds like it's been a bit of trial-and-error, which is not a good way for anything to be fixed (actually, sounds a lot like the troubles I had with my last new car and the dealership, so I feel your pain).

kcchen_00
Posts: 1721
Joined: Thu Feb 19, 2015 12:42 am

Re: Wiper Pad Alternatives

Post by kcchen_00 » Mon Nov 19, 2018 8:35 pm

Sounds like the filament isn't sticking to the bed... give the PEI a scrub with a scotch brite pad until its hazy.

IDEngineer
Posts: 43
Joined: Sun Feb 05, 2017 2:36 pm

Re: Wiper Pad Alternatives

Post by IDEngineer » Mon Nov 19, 2018 11:16 pm

mwester wrote:
Mon Nov 19, 2018 7:33 pm
I have to wonder if you're not suffering from overtemp.
I've tried reducing the temp to 200C. Right now I'm at 220C, and I've gone higher. No changes, same result regardless of temperature.

All of the above numbers are what Cura displays. See below for more accurate temp info.
So, I'm wondering if your filament is simply too hot, so that the retraction just stretches the filament, leaving some of it down in the hot-end, and the overly-hot hot-end melts what's there and drips it onto the bed.
Remember, the Mini's default sequence is:

1) Preheat the nozzle
2) Retract 30mm of filament
3) Wipe the nozzle
4) Finish heating the nozzle to 10C below the target temp
5) THEN push 30mm of filament into the printhead, to offset the 30mm of retraction in step 2

It is only at this step 5 that the dribbling occurs. So I don't necessarily think there's "leftover" filament in the nozzle... the machine is actively pushing filament into the head.
Yes, I do sometimes get some "pre-oozing" as the head heats up but before the 30mm push occurs, but the majority of the problem is after the 30mm starts.
One is that yu've replaced the fan that blows on the heat-sink, you stated above -- double-check that fan to make sure that it's pushing air through that head-sink.
Yep, definitely airflow through the nozzle and across the heaksink.
Another possibility is that you may simply have a bad thermister -- use an IR thermometer and check that the nozzle temp matches what the firmware is reading.
I have a calibrated Fluke contact thermometer. When Cura reports 220C, it reads 195C. This has been true since the Mini was brand new... the quality of the thermistors used by Lulzbot must be just awful. This machine has always had a roughly -25C offset from reality (the actual head temp is always ~25C lower than reported by the software).

I asked Lulzbot support where, in the firmware, the thermistor could be calibrated. I have 30+ years writing firmware and every time we work with sensors of any kind we always design in a way to enter a calibration value, even if it's just an offset to compensate for this sort of thing. This is just normal professional practice. Their response was "Nope, no way to do that." Seriously?!?

But in any case, I doubt we're looking at an overtemperature problem here. See below for more comments.
Regardless, the above doesn't address the lack of "stickiness" of the filament to the bed.
I had the same thought, which is why I started playing with the temperature. No matter what Lulzbot's firmware and Cura report as an absolute value, I just started making relative changes to see how things behaved. 220C displayed/195C actual seems to give me reasonable "squish" on the print bed without being so high that temperature further contributes to dribbling. Honestly, it's basically a balancing act trying to get this Mini to work at all.
Almost sounds as if there's something (like a layer of oil) on the PEI surface.
Remember, this is a BRAND NEW print bed straight from Lulzbot - their latest, most expensive version. And I clean the surface before every attempt with a bottle of alcohol that is dedicated to the printer and is sitting right next to it all of the time. No, I haven't roughed it up with ScotchBrite yet, but I would expect a factory-fresh print bed freshly cleaned with alcohol to work at least a little while.

BTW, I have managed to stop the printer before the entire first layer was ripped off, which allowed me to test the first layer adhesion to the bed. It feels fine - I think the blob on the nozzle just has a strong enough bond to overcome the normal adhesion force. There's supposed to be "interlayer adhesion" after all!

The root problem here is the blob of filament, the dribbling and oozing. It's done it since day one, even with the sample filament that Lulzbot included to print the Rocktopus.

EDIT: I've also tried flipping the print bed and printing PLA directly to the bare glass surface. No changes. The first layer adheres OK but the interlayer adhesion to the nozzle blob is still strong enough to rip the first layer away from the print bed.

Galadriel
Aleph Objects | LulzBot
Posts: 279
Joined: Mon Sep 25, 2017 10:23 am

Re: Wiper Pad Alternatives

Post by Galadriel » Tue Nov 20, 2018 3:30 pm

IDEngineer wrote:
Mon Nov 19, 2018 11:16 pm
Another possibility is that you may simply have a bad thermister -- use an IR thermometer and check that the nozzle temp matches what the firmware is reading.
I have a calibrated Fluke contact thermometer. When Cura reports 220C, it reads 195C. This has been true since the Mini was brand new... the quality of the thermistors used by Lulzbot must be just awful. This machine has always had a roughly -25C offset from reality (the actual head temp is always ~25C lower than reported by the software).

I asked Lulzbot support where, in the firmware, the thermistor could be calibrated. I have 30+ years writing firmware and every time we work with sensors of any kind we always design in a way to enter a calibration value, even if it's just an offset to compensate for this sort of thing. This is just normal professional practice. Their response was "Nope, no way to do that." Seriously?!?

But in any case, I doubt we're looking at an overtemperature problem here. See below for more comments.
I wanted to chime in on this as it sounds like there may have been a miscommunication or misunderstanding on this front. It is true that to go in and adjust the heat range of the thermistor you would need to modify your firmware which is something we don't support since there is a lot of chances for things to go wrong once you start messing with the firmware. That being said for the issue you are having of getting inaccurate readings changing the overall heat range of your thermistor isn't really what you would be going for. Something that might help would be completing a PID tuning on this toolhead.
Here are the instructions for tuning your PID:
Allow your hot end to cool to room temp. In the console in CURA, send the following command: M303 S230 if extruding ABS at 230. Change the number in the command to reflect the temperature at which you normally extrude. The M303 SXXX command will tune the extruder. Use M303 E-1 SXXX to tune the bed. The hot end will then heat up and finally cool, while logging the temperature. When completed, similar values will be displayed:

bias: 101 d: 101 min: 145.48 max: 154.02 Ku: 64.06 Tu: 29.67 Clasic PID Kp: 38.04 Ki: 2.35 Kd: 147.63

Enter that information into your Start Gcode in Slic3r using the following format, with your values substituted appropriately:

M301 P38.04 I2.35 D147.63 or for the heated bed: M304 P38.04 I2.35 D147.63

Enter the following command to save the PID settings to EEPROM.

M500

Reslice your model. Your temperature fluctuations should be lessened and more consistent.

Sorry about any confusion/miscommunication on this front!

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