Nozzle momentarily continues extrusion on completion ruining model

[Kenross1951 2]

Hi,

very new to this I have salvages a UM2 and have it up and running using Cura to prepare files.  The problem is that when the print job completes instead of the nozzle immediately leaving the work it remains there depositing material for a brief period which basically ruins the model.  The pictures of a cog being printed and the end result with the blob are attached. Is this a G-code issue or am I missing something fundamental.  Apologies if this has been covered before I searched but could not find anything.

 

Regards

 

Ken

[gr5 2,178]

This happens to me also occasionally and it's very annoying.  If you just print it again I think it won't happen the second time.

 

It doesn't happen often enough for me to figure out the cause.

 

It doesn't actually extrude during this time as far as I know - it just melts the part.

 

I've been there when it happens and I cut the power and push down the bed but it's often too late.

 

I've been tempted to manually add a Z move upwards at the end of the print job but never done it.

 

Since your part is so small, you could print a few of them in "one at a time" mode and only the last one will get ruined but again, I find this doesn't happen very often.

[gr5 2,178]

If it happens twice in a row, maybe you should post your gcode for me to look at.  Or at least the last 30 lines of gcode.  99% of the time I ask for the cura profile (file, save profile) but this time I think I want to see the actual gcode.

[Slashee_the_Cow 279]

/me looks at end g-code for UM2

;Version _2.6 of the firmware can abort the print too early if the file ends
;too soon. However if the file hasn't ended yet because there are comments at
;the end of the file, it won't abort yet. Therefore we have to put at least 512
;bytes at the end of the g-code so that the file is not yet finished by the
;time that the motion planner gets flushed. With firmware version _3.3 this
;should be fixed, so this comment wouldn't be necessary any more. Now we have
;to pad this text to make precisely 512 bytes.

 

Okay so I don't know if it's a good idea or not to try put stuff before that. Or if it has anything to do with the pause. Or if the pause is before or after it reaches the end g-code.

 

But let's assume it a best case scenario and the pause is after it's run all the g-code and adding commands won't mess with that bit at the end. The lines you'd want to put before that padding are, in theory:

G91 ; Relative positioning
G0 Z30 ; Move Z up 30mm

[gr5 2,178]

Note that if your print is very tall, moving up another 30mm might go "outside the bounds" of the printer volume and so it would just ignore that command and display an error message and defeat the whole purpose.  But anything at least 30mm short of the full height would be fine.

 

Yes that text at the end was to fix a bug in older um2 firmwares but I think the bug was fixed long ago.  Still, probably half the um2 printers out there have older firmware with the bug. 

[Kenross1951 2]

Thanks for the prompt response everyone. GR5, it has happened on 2 of the same part and a second part (the one in the pic) three in a row Neither part was tall.  I will post  the G-code when i go down to the workshop later this morning.

[Slashee_the_Cow 279]

This one is a little more annoying if you're printing short models (because it results in a long travel up at the end then down next time you want to do something) but if you want to make sure you don't go past the printer's Z limit:

G90 ; Absolute positioning
G0 Z205; Move to top of build volume

 

/me smells the potential to make a post-processing script and hopes Greg doesn't catch the scent

[Kenross1951 2]

OK, so the g-code for the cog and filament sharpener are attached, both parts had exactly the same result at conclusion. 

 

UM2_GEAR-11-V5.gcode UM2_sharpener.gcode

[Slashee_the_Cow 279]

1 hour ago, Kenross1951 said:

OK, so the g-code for the cog and filament sharpener are attached, both parts had exactly the same result at conclusion. 

What strikes me at first glance is the G10 (firmware retract) at the end - if that takes any amount of time (does the UM2 have a Bowden extruder? Because if it does, that does take a little bit of time) it'll just hover there while it does that.

 

Would need a post-processing script to make it move the head before that, I'll see if I can whip something up in a little bit.

[Kenross1951 2]

48 minutes ago, Slashee_the_Cow said:

What strikes me at first glance is the G10 (firmware retract) at the end - if that takes any amount of time (does the UM2 have a Bowden extruder? Because if it does, that does take a little bit of time) it'll just hover there while it does that.

 

Would need a post-processing script to make it move the head before that, I'll see if I can whip something up in a little bit.

Yes it is a Bowden extruder.

 

[gr5 2,178]

It should take less than 1/2 second to do the retract.

 

The gcode looks fine to me.  There is nothing in the gcode to move the Z up (or bed down) but there shouldn't need to be.

 

Adding a

G28 Z

 

might be best as that homes the Z axis which for the UM2 is when the bed is all the way down.  Maybe followed by:

G28 X Y

 

Which homes the x and y axes.  But you shouldn't need to do that.  The firmware should do that automatically at the end of the print.

[Slashee_the_Cow 279]

25 minutes ago, gr5 said:

Adding a

G28 Z

 

might be best as that homes the Z axis which for the UM2 is when the bed is all the way down.  Maybe followed by:

G28 X Y

You don't want to home the printer in the g-code after you print. Its normal home is at the base (often, but depends on printer) in the middle. If you home it in the g-code after it's finished printing it probably won't have any qualms trying to smash its way home, although might stop if something puts up enough of a fight.

 

Also worth noting: some printers do act on "comments" in the g-code, Cura includes comments which say how long it should have printed each layer, for all I know a UM2 could wait if the print time hasn't been that long.

 

@Kenross1951 Could you please provide the Cura project (.3mf file) for those parts so I can slice them myself and try some scripts?

[Kenross1951 2]

thank you, the end of the g-code for the gear is currently [G1 X112.967 Y108.241 E1460.62137
;TIME_ELAPSED:2485.849854
G10
M107]

 

where do I add the 'G28 Z'? after the G10 or before?

[Kenross1951 2]

I think this is the file I downloaded for the gear but it is an .stl

 

GEAR-11-V5.stl

[Slashee_the_Cow 279]

@Kenross1951 Thanks but I really need the 3mf file, as it contains printer information and print settings and such. Just load the STL in Cura and do what you'd do to get it ready to print then go to File > Save Project in Cura and you can save a 3mf file.

[Kenross1951 2]

here is the filament sharpener

sharpener.stl

[Kenross1951 2]

here they are fresh off the press!

UM2_GEAR-11-V5.3mf UM2_sharpener.3mf

[Slashee_the_Cow 279]

Ummm @gr5 I might need your help here - I try to open it and those UM2 3mfs in Cura (with a non-networked Ultimaker 2 profile added... there isn't a material dropdown?) and I get a crash about not having a material profile with the key "ultimaker_pla_red"

[Kenross1951 2]

Interesting I changed that setting because I bought a fresh roll of Ultimaker PLA red previously it was set to generic how odd

 

 

[Kenross1951 2]

Just swapped it back to generic try that

 

UM2_GEAR-11-V5.3mf

[gr5 2,178]

10 hours ago, Slashee_the_Cow said:

You don't want to home the printer in the g-code after you print.

This is true for an Ender 3 or any prusa style printer but for an Ultimaker 2 series the bed moves (not the print head which stays up in the gantry) and it moves down to home so it's the safest thing after a print and in fact the printer homes all axes automatically after the print is over.  But why it pauses for so long I don't know.

 

10 hours ago, Slashee_the_Cow said:

Cura includes comments which say how long it should have printed each layer

The only thing this is used for is to estimate how much longer it will take to finish the print.  That's the only thing that information is used for.  But good thinking outside the box.  🙂

[Slashee_the_Cow 279]

@gr5 I might need your help here - I try to open even generic 3mf Kenross1951 uploaded in Cura (with a non-networked Ultimaker 2 profile added... there isn't a material dropdown?) and I get a crash about not having a material profile with the key "ultimaker_pla_red".

 

14 hours ago, gr5 said:

for an Ultimaker 2 series the bed moves (not the print head which stays up in the gantry) and it moves down to home so it's the safest thing after a print

Oh god please don't make me do research before I try and help with any particular printer. I used to have a printer where the bed moved, and homing would be bad. But that's because the bed moved X and Y (teeth on the bottom, on motorised geared rods) and the nozzle would just move up and down. Although the homing process was more of a "force the bed to each corner to make sure the teeth hadn't slipped on any rods and put the bed at an angle" process... and yes it was necessary sometimes. Also the bed was plastic and not heated. And tiny. Also it cost US$300 in an Indiegogo campaign in 2013. I wasn't exactly spending Replicator money there.

 

Also: given I had not much better to do if anyone wants a post that moves the head up either a configurable distance (default is 30mm) or to the top of the build volume (whichever is lower... duh) just before the last ;TIME_ELAPSED comment just for kicks, here ya go.MoveUpWhenDone.zip Could be useful in general, I guess.

[gr5 2,178]

You don't need to add machine profiles.  When you open the 3mf file it will create the machine profile automatically.  I have like 3 different ender 3 profiles all pulled in from 3mf files and 2 of them must have been tweaked by the user or something.

 

Also why do you need the 3mf?  Also he created one for you with generic PLA so if it still doesn't work then something is wrong with your cura local files but cleaning that up will make you lose all profiles so I don't know what you can do @Slashee_the_Cow.  When I say "local files" I mean your installation is probably fine but the "customizations" are somehow messed up for the UM2.  The fix is normally to delete all those files and they will get recreated when cura launches.  But you will lose all your profiles and stuff that don't come with the fresh install of cura.

 

On 10/18/2023 at 11:28 PM, Kenross1951 said:

hank you, the end of the g-code for the gear is currently [G1 X112.967 Y108.241 E1460.62137
;TIME_ELAPSED:2485.849854
G10
M107]

 

where do I add the 'G28 Z'? after the G10 or before?

 

Either.  Both.

 

If you add it before the G10 then it will move before retracting so you might get a very very thin string moving upwards but at least it will sit there on the top of your print (potentially melting it) for a full 1/4 second less time.

 

If you add it after the G10 then it will retract before moving.

 

I'd try after the G10 and if it still pauses then I'd move it before the G10.  Then post what you learn.

 

That other move that starts with "G1" is the final printing move.  Note that it includes X, Y, E.  Those are the positions to move those 3 axes to in millimeters.  If it has an "E" then it's an extruding move.  M107 I think turns off a heater or fan.  You can google "reprap gcode" for details on what the gcodes do.  There are only about 10 gcodes used by cura so it's not a big deal to look them all up.

 

[Kenross1951 2]

Am I correct in assuming that I can edit the g-code created by Cura with a text editor, save and use it?  Or are there some arcane arts involved in the editing process?

[Slashee_the_Cow 279]

11 minutes ago, Kenross1951 said:

Am I correct in assuming that I can edit the g-code created by Cura with a text editor, save and use it?  Or are there some arcane arts involved in the editing process?

Nope, you're correct. I usually use Notepad++ myself, Windows' built in notepad doesn't handle large files very gracefully.