Underextrusion?
A short while back I got wax filament to work with the lost wax technique, and figured out how to print it. Just before I changed back to PETG I had a jam at the extruder motor. The filament got mangled and ended up feeding out sideways through the observation hole for the idler gear. I cleared the jam and loaded petg shortly afterwards. Since then I've had a progressive underextrusion issue.
PETG started printing with a rough matte finish and prints became brittle. It had gotten worse over time. At first if I slowed the print speed down by ten in the "tune" menu whilst printing it fixed the problem. Now, even if I set it to 40, it doesn't help anymore. I have cleaned the drive and idler gears (the had wax in the grooves) it helped. I shaved the PTFE tube a bit (it had become deformed at the top by the feed and idler gears from the wax jam) that helped. I realigned the feed gear(which was off slightly) and checked the axle on the idler gear. I adjusted the tension on the idler gear(it was too tight). I cleared a partial clog in the bottom of the PTFE tube where it goes into the heat break. Changed the nozzle three times(every time the underextrusion got slightly better). I checked the extrusion rate twice by marking the filament at 100mm then fed 100mm an measured the actual fed filament. When I started it fed 94mm. After the tuning I did it fed just over 99mm. I adjusted the multiplier to 1.01 to compensate(it barely helped) then adjusted the "flow" setting in the tune menu to 110(that helped more but if I set it higher the print shows signs of overextrusion, blobs, grooves from the nozzle, and clicking from the extruder motor after a few layers). The extruder motor gets much hotter than it used to.
If I do a cold pull the filament usually breaks at the melt point. The one time I got it to pull out there was a seam where the nozzle meets the throat, so I tightened the nozzle at PETG temp.
The only thing I can think of is that wax worked it's way into the extruder motor from that jam then melted due to heat and is putting excessive drag on the shaft. Before I attempt to remove the motor and take it appart to check I wanted to see if I missed anything.
Here are some pictures of a couple of test prints I did. The first 20 layers or so print perfectly. After that not so much. The one on the right was done at .15 layer height, and flow increased to 100 from the default of 95. I changed infil print speed to 120mm/s from the default of 200. The print on the left I raised the print temp to 245 from 230, changed the speed in the tune menu to 60 then 40 just above the letters on the front. The flow rate was 110, but everything else was the same.
I don't think this printer was made to barely print at .15 layer and 20mm/s, so something must be up. (It printed beautifully with pla, and the first petg prints I did.)
Thanks in advance, and any suggestions are greatly appreciated.
Re: Underextrusion?
Tyler, you have done an excellent job at troubleshooting!
If you are extruding plastic, but not enough (underextruding) and you've checked your calibration (which you have), then something is going wrong with the quantity of plastic pushed by the drive gears. The root cause, as you suggest, is usually some kind of obstruction in the path between the drive gears and the nozzle. But it's also possible for there to be too much drag on the filament coming from the feed spool to the drive gears, so you might want to check that. Sometimes there's a problem where the end of a filament got wrapped underneath a coil on the spool so you are essentially pulling against a knot, for example.
When there's too much back pressure or too much drag, then one of two things must happen: either the drive gears slip on the filament, or the extruder motor fails to turn as much as it's being commanded to turn. When a stepper motor fails to turn enough, it will "slip a cog" and move back by (at least) one full step length, and this slipping is always associated with an audible click. You can also see it visually through the observation port. (I just thought of a third possibility: the grub screw holding the drive gear onto the motor shaft might be loose, allowing the motor to turn while the gear does not.)
Did you build the printer from a kit? If so, you have the instructions in hand to tear down the extruder body enough to remove the motor. If you bought it assembled, you can find the assembly instructions online. It may take you a couple of hours the first time you do it, but it may be necessary. Once you have the motor and the drive gears removed from the extruder body, you can clean them very thoroughly of any wax, using a suitable solvent. Wax is pretty slippery and any residue on the gears could cause slipping.
By the way, the way that stepper motors are controlled means that they have almost perfectly consistent total current going through the coils at all times, so the motor doesn't get significantly hotter because it's stalling or fighting excessive drag; steppers differ from most other electric motors in that regard.
Re: Underextrusion?
Thanks for the suggestions.
It isn't the spool. I've had that issue before and look out for it now. The nut on the drive gear is tight. When I realigned it recently I made sure to tighten it so it wouldn't slip again.
I forgot to mention that on one of the nozzle changes I didn't tighten it at temp and when I took apart the hot end again there was a puddle of plastic on top of the heat block. I changed the nozzle after that and tightened it at 230c, but that's when I got the cold pull to work and saw the seam between the nozzle and throat. So I tightened it about an eighth of a turn more. The next cold pull broke off at the melt point again. I'm using cleaning filament to cold pull with.
I did build it from a kit and I've had the instructions open to the extruder section for a couple of days. I really don't want to pull it apart if I don't have to. It seems like I have to though. Also, I don't think my pictures uploaded. I'll try again now.
Re: Underextrusion?
You're right, none of your pictures are visible. Although there's an "Img" entry in the menu above the text-entry box, I always scroll down to the "Attachments" tab down below. In that tab, you can "Add Files" and then, once they have been uploaded, you can put them "inline" with the text. Be sure to put the cursor where you want the picture to go; do this AFTER uploading the pictures but BEFORE clicking on "Inline". 🙂
Re: Underextrusion?
I compared the original nozzle with one of the unused replacement nozzles and noticed that the new one has a slightly narrower inner diameter. I reinstalled the original, and did a couple of cold pulls. Now the printer works well again.
There are only two differences between the original and replacement nozzles that I can see. The replacement is steel and has a slightly narrower inner diameter. I'm thinking that the slightly larger reservoir is necessary for quality prints. I don't fully understand why, but it works. Thanks for the help.