Taz 6 and Extruder shooting blanks

In the short video you can see our school’s Taz 6 messing up the start of its print. Something like this happens every time.
Can anyone tell me why, just after the hot-end moves diagonally to the starting point of the print, the green gear whirls and the extruder backs the filament out some distance. When the print first begins, the extruder pushes filament forward but nothing comes out for a long time.

I checked out the Start Gcode as shown in Cura, but this filament backing movement takes place after the start code has been executed. I don’t know how to access that potion of the print instructions.

Any help would be appreciated.

I had the sense to get the video working via Youtube.
Thanks for watching.

It looks like it eventually starts to print okay. The retraction probably mitigates ooze at the beginning of the print. The retraction and wipe process are part of the start script.

I agree that doesn’t look correct. Lets take a look at your starting gcode.

Preferences > Configure Cura > Printers > Machine Settings > Start Gcode

The viewing box probably won’t be large enough, hover your mouse over the edge of the box and drag outwards to make larger. Click inside the Start Gcode text box, select all and copy the contents and post here, or post in a text file and upload it.

Also, your nozzle looks pretty far from the bed that’s why it isn’t sticking. What’s your Z offset set to? You can get that from the LCD panel Configuration, Z offset. Or use the software console M851.

Thirdly, you should always print a skirt at the very least to prime the extruder. I set the skirt to the minimums, 1 line and 25mm. If your perimeter is larger than 25mm it will continue to print the skirt for one entire loop. 2 loops if you were to set it to 2 lines, etc…

Thanks for replies!

I will post gcode start-code later when I am at the correct computer.
I know a little bit of python programming and as I looked over the Start GCode I saw quite a bit that was easy to understand, (But why is the start and end code viewing window so goofy?)
I am 90% sure that the quick filament retraction on the video takes place AFTER the Start GCode executes.

I played a little with z offset via LCD panel. Quickly realized I don’t know what is correct setting. Do changes made there in the LCD panel become permanent settings for the TAZ?

I usually (all of 2 weeks) print a skirt but I had so many failures it was driving me nuts.
The print in the video is a 1 layer test square to help me diagnose without wasting a ton of filament.

I will post the GCode later this morning but I do not think the problem is there.

Always always always print a skirt.

Depending on the size of the part you’ll need to adjust how many skirt lines you want.

Small parts may require 5 or 6 skirt lines.
Large parts may only need one skirt.

Skirts are your friend.

Below is the Start Code or Start GCode or whatever.
The rapid filament retraction takes place After the last line of this code is executed.

;This G-Code has been generated specifically for the LulzBot TAZ 6 with standard extruder

M75 ; start GLCD timer
G26 ; clear potential ‘probe fail’ condition
G21 ; set units to Millimetres
M107 ; disable fans
M420 S0 ; disable previous leveling matrix
G90 ; absolute positioning
M82 ; set extruder to absolute mode
G92 E0 ; set extruder position to 0
M140 S{material_bed_temperature} ; start bed heating up
M109 R{material_soften_temperature} ; soften filament before homing Z
G28 ; Home all axes
G1 E-30 F100 ; retract filament
M109 R{material_wipe_temperature} ; wait for extruder to reach wiping temp
G1 X-15 Y100 F3000 ; move above wiper pad
G1 Z1 ; push nozzle into wiper
G1 X-17 Y95 F1000 ; slow wipe
G1 X-17 Y90 F1000 ; slow wipe
G1 X-17 Y85 F1000 ; slow wipe
G1 X-15 Y90 F1000 ; slow wipe
G1 X-17 Y80 F1000 ; slow wipe
G1 X-15 Y95 F1000 ; slow wipe
G1 X-17 Y75 F2000 ; fast wipe
G1 X-15 Y65 F2000 ; fast wipe
G1 X-17 Y70 F2000 ; fast wipe
G1 X-15 Y60 F2000 ; fast wipe
G1 X-17 Y55 F2000 ; fast wipe
G1 X-15 Y50 F2000 ; fast wipe
G1 X-17 Y40 F2000 ; fast wipe
G1 X-15 Y45 F2000 ; fast wipe
G1 X-17 Y35 F2000 ; fast wipe
G1 X-15 Y40 F2000 ; fast wipe
G1 X-17 Y70 F2000 ; fast wipe
G1 X-15 Y30 Z2 F2000 ; fast wipe
G1 X-17 Y35 F2000 ; fast wipe
G1 X-15 Y25 F2000 ; fast wipe
G1 X-17 Y30 F2000 ; fast wipe
G1 X-15 Y25 Z1.5 F1000 ; slow wipe
G1 X-17 Y23 F1000 ; slow wipe
G1 Z10 ; raise extruder
M109 R{material_probe_temperature} ; wait for extruder to reach probe temp
G1 X-9 Y-9 ; move above first probe point
M204 S100 ; set probing acceleration
G29 ; start auto-leveling sequence
M420 S1 ; activate bed level matrix
M425 Z ; use measured Z backlash for compensation
M425 Z F0 ; turn off measured Z backlash compensation. (if activated in the quality settings, this command will automatically be ignored)
M204 S500 ; restore standard acceleration
G1 X0 Y0 Z15 F5000 ; move up off last probe point
G4 S1 ; pause
M400 ; wait for moves to finish
M117 Heating… ; progress indicator message on LCD
M190 S{material_bed_temperature_layer_0} ; wait for bed to reach printing temp
M109 R{material_print_temperature_layer_0} ; wait for extruder to reach printing temp
G1 Z2 E5 F75 ; prime tiny bit of filament into the nozzle
M117 TAZ 6 Printing… ; progress indicator message on LCD

I viewed video on youtube. Made it full screen.

It appears on the video that there’s quite large gap between the nozzle and the bed.

Could just be the angle, but it does look too big from the video.

On the Taz LCD screen, I find Z Offset. and i can “tune” it.
Will the value I change it to be saved automatically into memory or must I adjust it each time?

WAIT I found Store Settings.

I agree it does seem it happens after the start gcode; however this 2nd to last line does not look right.

You don’t have 6 extruders, that should be E0.

Fix that and see if that does anything for you…

Sorry Joe, but I believe you had a temporary brain fart :smiley:. G1 Z2 E5 F75 says at the current X and Y, move the nozzle height to 2 and extrude filament until the current E position is 5. Previously the extruder was set to absolute mode, the current filament position set to 0, and then a couple of commands later, the filament was retracted by 30. Therefore, the result of the E5 should be to extrude 5mm of filament.

Yes, thanks for catching that.
If I am understanding the gcode, the extruder is in Absolute mode, so that command to extrude E5 at the end of the start code meant the machine has to back the filament out to get back to E0.

I think I need to mess with z offset now.
I’ll post another video soon.

Ahhh ok, I thought E# was the extruder number. Thanks for explanation!

I communicated with students via email. Apparently they modified the gcode to prime the nozzle by extruding 5 mm of filament. Could have helped if we were in Relative mode.
Because the machine is in Absolute mode, it sets the filament back to E0 as part of the basic print instructions (i.e. after start gcode executes)
I’ll change z offset and make another video.

I messed around for over an hour not making much progress.
As soon as the print extrusion begins, the ABS curls back onto the nozzle as soon as it is squirted out. See videos.
Start of print
hand fed curl

I pushed filament through by hand at various nozzle temps: same result.
The nozzle is about 4 days old with perhaps 8 hours of heated time.

I did a cold pull. Maybe interior of nozzle is asymmetric/slightly clogged? See pics

I use eSun cleaning filament when my nozzle “gets the curls” and one or two cold pulls usually cures it.

What temp to you run it up to and when to pull it out?

The cleaning filament has a very wide temperature range. Use the temperature of the filament you are cleaning out (i.e. PLA 190-220, ABS 240-260, etc.). Extrude filament until there’s there’s no visible residue. Then cool things down and do the cold pull. If that comes out clean, you are done, if not, heat things up and go again.

I do cold pulls at 100-120. Experiment with the cold pull temperature until you get a good imprint of the inside of the nozzle. On my TAZ 6 Single Extruders, I can shine a light into the top of the tool head and see (with the help of a mirror) a nice round spot of light through the nozzle.

ABS is one of the most temperature sensitive filaments out there. I’m not surprised that as soon as hot ABS strings hit cold air, it curls.

ABS needs to be printed in an enclosure with an ambient temperature around the printer to be rather warm.

If you have some PLA try your “curl test” with that.

I’m guessing you’re just seeing what ABS does naturally.

ABS contracts like crazy when it cools. A thin string is going to curl when it cools.

Just my 2 cents.

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Yes, edlink is right.
After some cleaning and cold pulls I put a reel of PLA in and it seems to be extruding correctly without curls.

I thought all was well until the test piece began to warp and lift off the bed.

z offset is -1.35 right now.
i want to make a primitive enclosure and see how that changes things.