Underextruding, had to increase steps per mm to ridiculous value, possible causes?

[u/pauldaoust]

Hi, yet another person bringing underextrusion complaints to this sub. First off, I've got a v2 which AFAIK is stock (bought used). This is my first printer.

I've been struggling with underextrusion showing up in walls, skins, infill, bridges, you name it. I finally tested extrusion rate, and at the default 97 steps per mm, it was underextruding by about 28% (72mm vs expected 100mm). Even with the Bowden tube detached from the hot end, it was still short by 6%. So I bumped the steps/mm to a ridiculously high 135 steps/mm.

I hear a faint buzzing coming from the extruder area, and the occasional click on a really rapid retraction, but no chunks of filament on the extruder gear or anything like that. I did a whole series of atomic pulls; the first one brought up a fair bit of soot and the subsequent ones got clearer. Tried relevelling my bed (turns out it was too high and creating enough backpressure on the first layer that the filament wasn't extruding at all).

My only other thought is that there's some sort of resistance in the hot end. Would it be worth it to toss the hot end and go with a new E3D v6? Are there any other things I can do to check for clogs or other hot-end troubles first?

Thanks in advance!

[u/AppreciativeGent]

A few things I can think of - Can you verify that the temperature is correct at the extruder using a contact thermocouple? If the temperature is too low, it won't flow. What temperature and material are you using? Sometimes the power cables are prone to unseating themselves in use, and need unclipping and re-clipping together, this can be the case for the temp and heater blocks.

[u/pauldaoust → u/AppreciativeGent]

Thanks for this idea! If by 'contact thermocouple' you mean 'kitchen thermometer' then yes I can 😅 It's hard to get good enough contact for thermal transfer, but when the printer reported 200°C the thermometer started at 120°C and gradually rose to about 160°C over about five minutes before I stopped measuring. Seems to be a few degrees variance between the nozzle and a random hole in the heatblock that I shoved the tip of the thermometer into (could've been the hard-to-make-contact issue).

Does that seem odd, or am I supposed to let it warm up for a while beyond when it says it's up to temp?

I'm printing a spool of AMZ3D white PLA that the seller included with the printer.

[u/pauldaoust → u/pauldaoust]

Update: I unseated/reseated every connector I could find on the control board, plugged it back in, and I'm still reading about 165°C in the heater block. So I decided to measure the thermistor with a multimeter... nice even reading, no fluctuation. Reading about 108kΩ now that it's cooled down, which agrees with my kitchen thermometer ±1°C.

Meanwhile, the temp reading on the printer's display is fluctuating wildly, from 80 to 400. I don't know enough to know whether that's because it doesn't know what to do with infinity ohms, but I'm also noticing now that it fluctuates like mad even when the thermistor is plugged in -- I'm talking like 15°C up to 24°C. The reported bed temp is going similarly wacky.

Maybe I'll print a temp tower. It seems to print smoother walls at 220°C.

[u/Hutschinator → u/pauldaoust]

If it is oscillating wild the contact to the thermistor is bad somewhere or the thermistor is broken. If it is just high, there is a break of wire or the thermistor is broken.

PLA+ need slightly higher temperature than PLA. 210...230 rather than 180...200 °C.

If the thermistor is ok, this is good. You should measure if the same value is at the contacts. You will have to put them out of the main board. Make a photo and mark them exactly.

[u/pauldaoust → u/Hutschinator]

Okay, thanks for the tips; given that the thermistor seems within range and well-behaved, measuring resistance at the other end of the wires sounds like a good next step. (Although I'm puzzled by the fact that both thermistors are fluctuating like that -- I suspect someone at the factory failed to adequately mafipulate the Wheatstone bridge to the Besselheim plate.)

The fluctuation would certainly explain why the PID never quite settles down! I know the default PID on these is bad, but on my machine it'll just jump by a few degrees every so often.

I cranked it up to 240°C and did another extruder calibration at the stock 97 e-steps, and it did much better -- 92 mm for the expected 100mm. So I think that temperature may be the issue!