Nozzle momentarily continues extrusion on completion ruining model

[Kenross1951 2]

Thank you folks.  OK so partial success, the filament retracted immediately and the bed dropped but a nano second afterwards the nozzle gave a final squirt as you can see in the second pic. The end of the g-code was:

 

 

;TIME_ELAPSED:3622.057960
G28 Z
G10
G28 Z
M107

;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.

M82 ;absolute extrusion mode
;End of Gcode

 

The product was unscathed which was a pleasant surprise. 

 

Any suggestions on why the post print squirt cause?

 

[gr5 2,179]

Okay so this is new information.  I didn't believe you when earlier you said the nozzle kept extruding.

 

This is 90% most likely from the G10.  Which is surprising.  G10 is supposed to retract but it looks like it is extruding.  A lot.  I've seen this before on UM2 printers.

 

I noticed that this seemed to happen consistently if I messed with the "flow" on the printer.  If I adjust the flow manually in the TUNE menu.  What would happen is it translates all the E values (the extrusion amounts) by the flow percentage.  And at the same time it is keeping track of two positions now - the virtual position of the E drive and the actual position.  Then at the end somehow it uses the wrong value I think.  That's my theory.  I never really figured it out.  My fix was to just adjust the flow in cura (which does all the math internally and sends the adjusted E values into the gcode file).

 

Anyway - did you mess with flow manually on the printer?

[gr5 2,179]

Possibly related - this isn't a "plus" printer - at least the print head is the "classic" print head.  Possibly you have a "plus" feeder.  The original feeders are black and the "plus" feeders are white and have a lever sticking out the side of the feeder that you can use to manually insert and remove filament.

[Kenross1951 2]

9 hours ago, gr5 said:

Okay so this is new information.  I didn't believe you when earlier you said the nozzle kept extruding.

 

This is 90% most likely from the G10.  Which is surprising.  G10 is supposed to retract but it looks like it is extruding.  A lot.  I've seen this before on UM2 printers.

 

I noticed that this seemed to happen consistently if I messed with the "flow" on the printer.  If I adjust the flow manually in the TUNE menu.  What would happen is it translates all the E values (the extrusion amounts) by the flow percentage.  And at the same time it is keeping track of two positions now - the virtual position of the E drive and the actual position.  Then at the end somehow it uses the wrong value I think.  That's my theory.  I never really figured it out.  My fix was to just adjust the flow in cura (which does all the math internally and sends the adjusted E values into the gcode file).

 

Anyway - did you mess with flow manually on the printer?

I haven't touched the flow I think it is currently set to 100% what is it normally set to?

[gr5 2,179]

100%

 

Well then I don't know why it does this long extrusion.  I have 3 um2go's and a um2 and I haven't seen this behavior in probably 5 years.

[Kenross1951 2]

The feeder is the black one, I cannot seem to find the "flow" setting but I know I have come across it in my wanderings in the menu's

 

[Slashee_the_Cow 291]

I don't know the retraction value of the of the UM2 (@gr5 this is where you might want to pop in and help) but you could try replacing the G10 with a

G91 ; Relative positioning
G1 E-4 F2500

(Probably want to wait for @gr5 on the exact retraction value; that's just what my E3V2Neo (with a bowden extruder) used).

 

This should hopefully just retract the filament instead of the firmware doing whatever the hell it does in a firmware retraction.

[Kenross1951 2]

Thank you for the suggestion will wait and see what @gr5 suggests 🙂

[gr5 2,179]

The retraction is set on the actual printer.  The default I think is 4mm as Slashee suggests.

 

Note that you DO NOT have a "plus" so if you have the "plus" firmware that could be your entire problem and no need to read further until you fix the firmware.

 

reset to factory defaults

 

Hmm.  So now I'm thinking the firmware normally retracts an extra amount at the very end of the print.  I forgot about that.  Like 20mm normally.  On purpose.  And it's not in the gcode it does it automatically.  So now I'm thinking the retraction is part of the firmware (like it's supposed to retract 20mm but your version is extruding 20mm or something) and now that makes me realize something.

 

There is a special area of memory on the arduino chip.  There is the ram, there is the eeprom that stores the firmware and there is this 3rd area that is basically another eeprom.

 

Marlin (the firmware on UM2 printers) stores a bunch of things in here like leveling Z height, how tall the printer is (um2go, um2, um2ext have different values), and about 200 other parameters (where to move to prime the nozzle, a list of known filament types and what temp and things to print them at, what fan speed).  One of those parameters might be the "retract at end of print job amount".  It probably unretracts the same amount right at the start of printing before it primes.  Maybe.

 

Anyway - this area can be corrupted when you change firmwares.  There is a data version number (similar to a firmware version) and anytime someone added or changed the data that goes in this special location, they would increment the firmware version.  And there is a pretty big chunk of code that when you boot after a new firmware install, it looks at the version number and automatically moves all the data as needed and fills in default values as needed to the latest version.

 

That chunk of code of course can only understand older firmware.  It's impossible for older firmware to know the future and know how to translate the other direction.

 

If anyone *ever* downgraded the firmware, what happens is it can get wild values in there.  The value for where to prime might get stored in the location for final retraction and what should be 20 is now 200.  The fix is to do:

RESET TO FACTORY DEFAULTS

 

Something like that - it's somewhere in the menu system on the printer.  It's annoying because now it thinks it is a brand new printer and you have to level it again and you use all your odometer-like counters.

 

Before you do this write down how many hours the printer has been printing and any other information like that!

 

 

option 3: switch to marlin flavor gcode

 

Another thing to try is to switch to Marlin flavor gcode.  The um2 has it's own special flavor of gcode.  For example the G10, G11 commands are unusual in Marlin (but part of the standard) and many printers don't support that so Cura can output the "E-4" like command for retraction that slashee suggests by changing one thing in Cura.  It's in the machine settings.  Without looking right now - go to PREPARE mode on screen and towards top left click on your printer and then look for machine settings and in there you have a few options for gcode flavor.  If it's on UM2 flavor switch to marlin I think?  Just try one of the other options.

 

I don't recommend this route as personally I prefer controlling fan speed, temperature, etc on the printer.  I have multiple UM2 printers and they each have different temps for the bed temp but with um2 flavor gcode I can print the same job on each printer.

 

When you change the flavor you will suddenly see about 20 new parameters appear in cura which control nozzle temp, bed temp, fan speed, filament diameter, retraction distance, and more.

[Kenross1951 2]

Update:  I decided to backtrack and follow your advice.  I factory reset the machine and then updated the firmware resliced the gear file and it printed flawlessly.

On another point, I have been trying to determine the date of manufacture of the unit from the serial number without any luck as I understand that the feeder settings  changed after 2014.  After some experimentation I determined that with the feeder tension set to the pre 2014 setting (right up) the filament could actually be pulled out with very little effort suggesting to me that it is a post 2014 unit.. I have the feeder setting now in centre and this seems to work fine. Thank you very much for your advice.

Edited October 23, 2023 by Kenross1951

[gr5 2,179]

You can email tech support with the serial number and they can tell you who the reseller is and when it was built.  Support is free as long as they don't have to send you any parts. on top right of this page click the nine dots, then "support" then on the top of the screen "submit a request".

 

Your excuse for mailing them can be "do I have the newer feeder" or something like that.

 

[gr5 2,179]

by the way I hope you wrote down how many hours your printer has been used.  It's possible that particular data is not erased on a factory reset - not 100% certain.

[gr5 2,179]

So it seems the solution was a "factory reset".  More details 4 posts up.

[Kenross1951 2]

Which is interesting because the first thing I did when I salvaged this unit was factory reset it.  Something must have not worked with that reset.  Anyway it appears to be working fine now thanks again

 

[gr5 2,179]

Well you have to do factory reset *after* you update the firmware.  It's the firmware change that messes up the settings (if you downgrade or move to a side version like tinker marlin).

 

[Kenross1951 2]

Well that would explain what happened because I assumed that the reset was before the firmware not the other way around.

1 hour ago, gr5 said:

Well you have to do factory reset *after* you update the firmware.  It's the firmware change that messes up the settings (if you downgrade or move to a side version like tinker marlin).