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Initial print Blob  

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Antimix
(@antimix)
Estimable Member
Initial print Blob

Hello,

when my MK3S starts to print, there is always the filament feed, and then printer starts doing a big plastic bubble on the bottom left angle of the bed, to ensure the pressure and plastic is really feeding through the nozzle, and then it does a double line from left to right and right to left. I always hate it, and quickly remove it as the head moves to right, to avoid the nozzle touch it when it return from right to left, to avoid it jams the outside of the nozzle. I do not change the gcode, since this action is however required for a proper print.

All till half an hour ago, when for first time in the printer life, the nozzle went to the extreme left of the printer, and when it extruded the plastic, I noticed that (don't ask me how) the nozzle was just few mm outside the plate, and all the plastic was melted on my table 😊 , without creating any blob on the bed. Then it moved and started to print normally.

I could have positioned the magnetic bed by accident few mm too far at right, and caused the material to be dropped on the table. But in any case I LOVE IT 😍. I will try to replicate this with other prints.

That raised me a question:

- Do you have the same behavior, with your Prusa ? When you start to print you get a blob of material on the bed , or your Prusa extrudes the plastic outside the bed dropping it on your table ??? 🙄 

Regards

Posted : 16/04/2020 12:59 pm
kpreid
(@kpreid)
Trusted Member
RE: Initial print Blob

Yes, I see the same blob (and there have been a few other reports). However, for some reason it only happens in MMU2-single slicing mode; multimaterial prints start extruding in the middle of the purge line instead.

I mean to see if the start gcode can be tweaked to eliminate it, but I haven't gotten to experimenting with it.

I also suspect that this blob is due to poor unloading and hence might be blamed on mechanical or temperature problems rather than software; for me the blob is always made of the previous filament color, not the newly loaded filament. My understanding is that the MMU2 unloading is supposed to succeed in removing most of the filament from the hotend, not leave that much material behind.

Posted : 16/04/2020 2:28 pm
Antimix
(@antimix)
Estimable Member
Topic starter answered:
RE: Initial print Blob

@kpreid

I agree, and for this reason I do not remove the logic from g-code.

However I should understand how to extrude it outside of the bed. It happened by chance. I was not able to repeat this event. Now, as usual it extrude the blob on the bed, and out outside.

Posted : 16/04/2020 5:05 pm
kpreid
(@kpreid)
Trusted Member
RE: Initial print Blob

I've seen that effect myself once or twice, I think usually because the sheet was not on the heatbed straight.

I've thought of modifying the gcode to extrude a mm or so above the bed (making a rounder blob instead of engulfing the nozzle) then moving down and +X to start the wipe. It would have a risk of loose bits getting snagged, though.

Posted : 16/04/2020 5:23 pm
jeroen.d3
(@jeroen-d3)
Eminent Member
RE: Initial print Blob

I have that blob with literally every print. I got used to it to be honest, printing over a year now in single mode via the MMU2. Somehow wanted to know more about it just now 😉

gcode at the beginning:

G80 ; mesh bed leveling
G1 Y-3.0 F1000.0 ; go outside print area
G92 E0.0
G1 X60.0 E9.0 F1000.0 ; intro line
M73 Q0 S20
M73 P0 R20
G1 X100.0 E12.5 F1000.0 ; intro line
G92 E0.0
M221 S95
G21 ; set units to millimeters
G90 ; use absolute coordinates
M83 ; use relative distances for extrusion
M900 K45 ; Filament gcode

Posted : 17/04/2020 2:01 pm
bobstro
(@bobstro)
Illustrious Member
RE: Initial print Blob
Posted by: @antimix

[...] when my MK3S starts to print, there is always the filament feed, and then printer starts doing a big plastic bubble on the bottom left angle of the bed, to ensure the pressure and plastic is really feeding through the nozzle, and then it does a double line from left to right and right to left. I always hate it, and quickly remove it as the head moves to right, to avoid the nozzle touch it when it return from right to left, to avoid it jams the outside of the nozzle. I do not change the gcode, since this action is however required for a proper print.

That doesn't sound like the normal Prusa prime line. The Prusa routine is a shorter, variable-width line. I see the long double-line in many of the other printer variants. Did your gcode originate with Prusa?

I'm doing a 2-step filament warmup to avoid oozing dots during mesh bed leveling. It extrudes a small blob without movement at the start of the prime line to trap any ooze from the previous print. I've seem more dramatic versions of this used. If you've customized your startup gcode (sounds like you have) that may be the origin of the blob. You certainly can remove it from the gcode. I've fully documented my 2-step warmup and prime process. Take a look there for ideas any possible inspiration. Line 53 extrudes 2mm of filament for a small trap blob.

All till half an hour ago, when for first time in the printer life, the nozzle went to the extreme left of the printer, and when it extruded the plastic, I noticed that (don't ask me how) the nozzle was just few mm outside the plate, and all the plastic was melted on my table 😊 , without creating any blob on the bed. Then it moved and started to print normally.

Again, not what you typically see with Prusa startup gcode. Prusa moves the head to X0,Y-3 for the prime line. However, my new Artillery Sidewinder shipped with sample startup gcode in the test print that moves off the bed boundary to extrude. Of course, you have to watch for odd bits of extruded filament floating around your print area this way, but it is effective on removal. I've seen people rig up wire brushes to one side to clean the nozzle this way.

I'm not sure that the actual physical move limits are on the Mk3. Mine's tied up now, but when it frees up, I'll see just how far I can move XY.

My notes and disclaimers on 3D printing and miscellaneous other tech projects
He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan...
Posted : 17/04/2020 5:06 pm
Peter in Katy
(@peter-in-katy)
Estimable Member
RE: Initial print Blob

@bobstro

The extra long, double prime line is part of the MMU startup code.  

Posted : 17/04/2020 5:17 pm
bobstro
(@bobstro)
Illustrious Member
RE: Initial print Blob
Posted by: @peter-k42

[...] The extra long, double prime line is part of the MMU startup code.  

Ah, thanks. I meant to mention that but forgot. Is it particularly important to the MMU? Are bed movements restricted by the MMU?

My notes and disclaimers on 3D printing and miscellaneous other tech projects
He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan...
Posted : 17/04/2020 5:30 pm
vintagepc
(@vintagepc)
RE: Initial print Blob
Posted by: @bobstro
Posted by: @peter-k42

[...] The extra long, double prime line is part of the MMU startup code.  

Ah, thanks. I meant to mention that but forgot. Is it particularly important to the MMU? Are bed movements restricted by the MMU?

I assume it's longer than normal to account for the initial load from empty potentially having some "air" in the hot end since it can't purge freely like a normal load well above the bed.

Posted : 17/04/2020 5:42 pm
Roger
(@roger-3)
Active Member
RE: Initial print Blob

Is this going to be fixed in the next update? It's been a problem for ages, it needs fixing properly by Prusa.

Posted : 26/05/2020 6:41 pm
Chocki
(@chocki)
Prominent Member
RE: Initial print Blob

This is my purge line (Non MMU) which I have been using for over a year now, I think it leaves a cleaner start than the default prusa purge line and stops that annoying dragging of a gossamer attached onto the print head by sticking a blob down at the beginning, it also carries out the purge higher than the prusa purge, there really is no need to squeeze the purge line into the bed.. Also I think the extrusion rate is too high so have adjusted mine, this is for the 0.4mm nozzle E6 and E9 are plenty good enough. The -5 and +5 move the nozzle back into the melted plastic, just enough to stick any deposit to the purge line, and the final G1 Z0 dabs the head removing anything if still left on the nozzle. I use a nickel plated copper nozzle with PETG and this keeps the nozzle clean.

G1 Z0.6 ; move slightly above bed for easy clean intro line
G1 E5.0 F1000.0 ; squirt a blob to stick any gossamer threads to the print bed before movement
G1 X60.0 E6.0 F1000.0 ; intro line
G1 X100.0 E9.0 F1000.0 ; intro line
G1 X95.0 E0 F1000.0 ; -5mm intro line @ E0 to wipe other side of nozzle
G1 X110.0 E0 F1000.0 ; +5mm intro line @ E0
G1 Z0 ;lower head back to normal Z after intro line

This post was modified 2 years ago by Chocki
Normal people believe that if it ain’t broke, don’t fix it. Engineers believe that if it ain’t broke, it doesn’t have enough features yet....
Posted : 31/05/2020 1:15 pm
Roger
(@roger-3)
Active Member
RE: Initial print Blob
Posted by: @chocki

This is my purge line (Non MMU) which I have been using for over a year now, I think it leaves a cleaner start than the default prusa purge line and stops that annoying dragging of a gossamer attached onto the print head by sticking a blob down at the beginning, it also carries out the purge higher than the prusa purge, there really is no need to squeeze the purge line into the bed.. Also I think the extrusion rate is too high so have adjusted mine, this is for the 0.4mm nozzle E6 and E9 are plenty good enough. The -5 and +5 move the nozzle back into the melted plastic, just enough to stick any deposit to the purge line, and the final G1 Z0 dabs the head removing anything if still left on the nozzle. I use a nickel plated copper nozzle with PETG and this keeps the nozzle clean.

G1 Z0.6 ; move slightly above bed for easy clean intro line
G1 E5.0 F1000.0 ; squirt a blob to stick any gossamer threads to the print bed before movement
G1 X60.0 E6.0 F1000.0 ; intro line
G1 X100.0 E9.0 F1000.0 ; intro line
G1 X95.0 E0 F1000.0 ; -5mm intro line @ E0 to wipe other side of nozzle
G1 X110.0 E0 F1000.0 ; +5mm intro line @ E0
G1 Z0 ;lower head back to normal Z after intro line

Thanks for sharing that. To be honest, even if that was suitable for the MMU2, I really don't think it's up to the end user to fix these things.

Hopefully someone at Prusa is looking at these posts and integrating a solution. I want to use the printer, not be a system developer.

Posted : 31/05/2020 3:44 pm
jaminnash
(@jaminnash)
New Member
RE: Initial print Blob

@chocki

Thanks for posting your code. I'm new to using the Prusa slicer. Do you add those lines to your start G-code? Do you need to have the printer warm the head and bed first?

 

Posted : 12/02/2021 4:15 pm
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