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andy.j3
(@andy-j3)
Active Member
Preliminary Purge Strip Question

I get different looking initial purge strips from time to time and im not sure what is causing it. Usually it has a big blob like this (see photo) then a little break then it starts laying down again and then it returns back. here is an ASCII version of what is happening for those that dont see the photo: O.....------------------------

Do you guys get this same "blob" at the beginning of each print? Is this normal?

Posted : 18/10/2019 3:51 pm
Chocki
(@chocki)
Prominent Member
RE: Preliminary Purge Strip Question

That blob is probably where your nozzle has started to ooze as it is coming up to temperature and the blob sticks to the sheet as the purge begins.

I modded my purge as I found it was just too much and now get much cleaner starts without so much material stuck to the nozzle.

Here is the start and end  G-Code:

START:

M115 U3.5.1 ; tell printer latest fw version
M83 ; extruder relative mode
G28 W ; MUST FIRST home all without mesh bed level or else risk nozzle crash!
G1 X10 Y200 Z110 F1000
M104 S150 ; preheat extruder to no ooze temp to help clean deposits
M109 S150 ; wait for extruder temp
M1 S10 ; Wait approx 10s to allow time to clean nozzle ooze then continue without user intervention.
G0 X70 Y70 Z0.5 F1000; PINDA warms faster near bed
M140 S[first_layer_bed_temperature] ; set bed temp
M190 S[first_layer_bed_temperature] ; wait for bed temp
M860 S35 ; wait for PINDA temp. For most stable PINDA temp during mesh, set temp here 1-2 deg below your actual PINDA temp at end of mesh cal.
M104 S100 ; drop extruder to lower temp to minimize PINDA temp rise during mesh
G80
G1 Y-3.0 F1000.0 ; go outside print area
G92 E0.0
G1 Z3 ; raise head safely clear of bed before heating extruder
M104 S[first_layer_temperature] ; we heat extruder AFTER mesh to minimize ooze
M109 S[first_layer_temperature] ; wait for extruder temp
G1 Z0.6 ; move slightly above bed for easy clean intro line
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 X100.0 E0 F1000.0 ; +5mm intro line @ E0
G1 Z0 ;lower head back to normal Z after intro line
G92 E0.0
M221 S{if layer_height==0.075}100{else}95{endif}

END:

G1 E-0.6 F2100;Anti stringing retract at end of print
G4 ; wait
M221 S100
M104 S0 ; turn off temperature
M140 S0 ; turn off heatbed
M107 ; turn off fan
{if layer_z < max_print_height}G1 Z{z_offset+min(layer_z+30, max_print_height)}{endif} ; Move print head up
G1 X0 Y200; home X axis
M84 ; disable motors
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 : 18/10/2019 5:02 pm
andy.j3
(@andy-j3)
Active Member
Topic starter answered:
RE: Preliminary Purge Strip Question

Thank you for the response. this isnt oozing, its an actual purge that gets pushed out while the head stays stationary in the bottom left... then it moves. it is very strange.

How do i mod my machine like that? will update "un-mod" it? do i have to do this for every print?

Posted : 18/10/2019 5:20 pm
richard.l
(@richard-l)
Moderator
RE: Preliminary Purge Strip Question

I know many of the Print Profiles created by Chris Warcocki have this, which he calls a purge bubble I believe. If the Print Profile starts with Pretty there's a good chance it was created by him.

...
Posted : 18/10/2019 6:00 pm
andy.j3
(@andy-j3)
Active Member
Topic starter answered:
RE: Preliminary Purge Strip Question

@richard-l

Good though but I am using the standard profiles from Prusa

Posted : 18/10/2019 6:59 pm
bobstro
(@bobstro)
Illustrious Member
RE: Preliminary Purge Strip Question

Are you printing gcode prepared by others? If so (e.g. downloads from prusaprinters.org) it's very likely you're running into different startup gcode settings. Some people like to extrude a blob of filament at the start of the prime line to trap any ooze off the nozzle before the start of the print. I do a small "blort" at the start of mine, but I've seen some that look like miniature Hershey's chocolate kisses.

Best would be to slice parts yourself and use the startup gcode that you prefer.

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 : 18/10/2019 7:21 pm
andy.j3
(@andy-j3)
Active Member
Topic starter answered:
RE: Preliminary Purge Strip Question

@bobstro

Another good idea but no. I slice and generate 100% of my GCode files myself. I dont use other people's GCode.

Posted : 18/10/2019 7:37 pm
bobstro
(@bobstro)
Illustrious Member
RE: Preliminary Purge Strip Question
Posted by: @andy-j3

@bobstro

Another good idea but no. I slice and generate 100% of my GCode files myself. I dont use other people's GCode.

At this point, I'd say zip and upload a 3MF project file and created gcode and let us look it over. If the print proceeds fine otherwise, I suspect the startup gcode is the culprit. Do you see a line that looks like:

G1 Exx  

Anywhere in the gcode? The lack of either X or Y coordinates with an E parameter corresponds to extrusion without movement.

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 : 18/10/2019 7:47 pm
andy.j3
(@andy-j3)
Active Member
Topic starter answered:
RE: Preliminary Purge Strip Question

Great Idea @bobstro! Here is a Benchy I Sliced in Prusa 2.1.0 just now.

I also attached a GCode file.

This post was modified 2 years ago 2 times by andy.j3
Posted : 18/10/2019 7:57 pm
gnat
 gnat
(@gnat)
Noble Member
RE: Preliminary Purge Strip Question

Mine does it too. The bubble seemed to show up after PS 2.0 received some profile updates about halfway between it's release and the 2.1 release. Similarly the purge line itself no longer seems to be as consistent as it once was (sometimes it can take not lay down plastic at all during the rightward movement).

I've just assumed that the pre-blob was related to the retraction from the last print as my unscientific data gathering seems to indicate that it is bigger if the prior print failed and it did not go through the normal ejection process.

Whatever the cause, the print itself works fine which is all I care about 😉 

MMU tips and troubleshooting
Stop SL1 tank leaks with a simple o-ring...
Posted : 18/10/2019 8:00 pm
andy.j3 liked
--
 --
(@)
Illustrious Member
RE: Preliminary Purge Strip Question

I got blobs with earlier versions of slicer and those profiles; and I am NOT getting blobs with the present incantation.  The startup gcode for the purge line from then to now is virtually identical.  The blobs I've experienced are all 100% ooze related.  No extrusion motor spin needed.

Posted : 18/10/2019 8:09 pm
andy.j3
(@andy-j3)
Active Member
Topic starter answered:
RE: Preliminary Purge Strip Question

@tim-m30

I can see the E-Axis spinning pushing filament out creating a small blob/mound and THEN it starts to move to right. While it does ooze during the 7x7 calibration... but its not ooze for this.

Posted : 18/10/2019 8:13 pm
andy.j3
(@andy-j3)
Active Member
Topic starter answered:
RE: Preliminary Purge Strip Question
Posted by: @tim-m30

I got blobs with earlier versions of slicer and those profiles; and I am NOT getting blobs with the present incantation.  The startup gcode for the purge line from then to now is virtually identical.  The blobs I've experienced are all 100% ooze related.  No extrusion motor spin needed.

What is a "preset incantation"?

Posted : 18/10/2019 8:17 pm
bobstro
(@bobstro)
Illustrious Member
RE: Preliminary Purge Strip Question
Posted by: @andy-j3

Another good idea but no. I slice and generate 100% of my GCode files myself. I dont use other people's GCode.

Are you using PrusaSlicer? Or Cura perhaps? Anybody's custom slicer profiles?

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 : 18/10/2019 8:22 pm
andy.j3
(@andy-j3)
Active Member
Topic starter answered:
RE: Preliminary Purge Strip Question
Posted by: @bobstro
Posted by: @andy-j3

Another good idea but no. I slice and generate 100% of my GCode files myself. I dont use other people's GCode.

Are you using PrusaSlicer? Or Cura perhaps? Anybody's custom slicer profiles?

I exclusively use PrusaSlicer. just the preset profiles from Prusa, nothing custom.

Posted : 18/10/2019 8:23 pm
--
 --
(@)
Illustrious Member
RE: Preliminary Purge Strip Question

If the extruder is turning and the nozzle is not moving, you have a mechanical problem: loose gear on the X-motor most likely.

Flat First: Drive gears must be tightened flat-first.

1)   Start with both set screws fully loosened so the pulley is free to spin on the motor shaft.

2)   Align one set screw dead center with the flat on the motor shaft, slowly tighten the screw until it fully contacts the flat surface.

3)   Torque the flat set screw to spec.

4)   Now tighten the jam set screw, and torque it to spec.

Once tightened, never touch the flat set screw unless the jam screw is first fully loosened.

Why Flat First? Set screws have flat ends. If you tighten the jam screw first the set screw on the shaft flat doesn't fully contact the shaft, only one small edge of the screw surface is biting. Reversing torques can easily shift the shaft to a position the flat screw no longer contacts the shaft. This lets the jam screw wriggle loose. And after a while, vibration loosens the screws until the gear is free to rotate.

Posted : 19/10/2019 9:33 am
gnat
 gnat
(@gnat)
Noble Member
RE: Preliminary Purge Strip Question
Posted by: @tim-m30

If the extruder is turning and the nozzle is not moving, you have a mechanical problem: loose gear on the X-motor most likely.

There is no requirement for X, Y, or Z to be moving while it is extruding, thus with no further indicators assume an assembly issue is a leap.

In this case the blob is being formed during the initial tool change which is why I suspect an incomplete/improper prior unload.

MMU tips and troubleshooting
Stop SL1 tank leaks with a simple o-ring...
Posted : 19/10/2019 1:49 pm
bobstro
(@bobstro)
Illustrious Member
RE: Preliminary Purge Strip Question
Posted by: @andy-j3

Great Idea @bobstro! Here is a Benchy I Sliced in Prusa 2.1.0 just now.

I also attached a GCode file.

Sorry, don't see either file attached. 

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 : 19/10/2019 3:26 pm
bobstro
(@bobstro)
Illustrious Member
RE: Preliminary Purge Strip Question

@andy-j3 we could clear up a lot of this if we could see your extruder visualizer in the video:

  • If that noisy blob is created with extruder movement, I'd bet on it being a gcode issue.
  • If that noisy blob is created without extruder movement, I'd look at ooze.

Would also like to see the 3MF if possible!

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 : 19/10/2019 3:31 pm
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 --
(@)
Illustrious Member
RE: Preliminary Purge Strip Question

So - folks are thinking the printer homing, doing them mesh level, then extruding in place prior to the purge line is expected behavior?

Andy - didn't you say that you have inconsistent purge lines? They can change from run to run?

Posted : 19/10/2019 6:50 pm
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