Feeder skips back every couple of seconds

[stevenpetrone 0]

Hello, sometimes when printing I notice my feeder on the back will push the filament up for a couple seconds and then skip back about 120 degrees pulling the filament back too. Sometimes I get under extrusion, however I am not sure if it's linked. Is this a normal thing; is the printer programmed to do that to regulate material flow? Or is this something that shouldn't be happening?

[DidierKlein 729]

There are two different behaviours with the feeder:

1. The feeder skips a step, you will hear a "tick" sound, the filament isn't pulled back, this happens when for a reason or another the feeder can't push the filament as it should. This prevents the feeder from grinding the filament. It can happen for multiple reasons: partially clogged nozzle, bad filament (too wide), worn out teflon, bad print settings (too cold, too fast).

2. The feeder pulls the filament back, no tick sound is heard, this is due to retractions, they happen on purpose to prevent the nozzle from oozing and dripping on the print.

What it the behaviour you're experiencing?

[gr5 2,094]

couple seconds and then skip back about 120 degrees pulling the filament back too

This has many names - such as "feeder skips". It's by design. The current sent to the feeder is purposely reduced such that it will skip back before hopefully before grinding the filament. On the UMO it tends to grind the filament.

As a result you get gaps for several seconds where it's not printing much.

The normal fix, for a working printer, is to print a bit slower or a bit thinner layers or a bit hotter. Although it's possible your printer is defective. In general this issue is called underextrusion. Anyway if you have the nozzle hotter, the plastic is less viscous and you can pass more volume of plastic through the tiny nozzle. At lower temperatures you can pass less. It's not recommended to go over 240C for PLA.

Here are top recommended speeds for .2mm layers (twice as fast for .1mm layers):

20mm/sec at 200C

30mm/sec at 210C

40mm/sec at 225C

50mm/sec at 240C

The printer can do double these speeds but with huge difficulty and usually with a loss in part quality due to underextrusion.

[gr5 2,094]

Please also indicate that you have a UM2 and what country you live in on your profile. This information affects the advice you will get on this forum as support options vary from country to country and the names of products and where to get them (like rubbing alcohol) vary also.

[diettelo 5]

I've got an something special.

Unleveld bed prints perfect 33 pieces on 1 bed. Leveld bed with 0.1mm print gets always later skip back

Print layer: 0.2 mm

Speed: 50

Retraction 40 4.5

Temp: 215

Pla

Before it printed perfectly also cleaned noozle. may to cold with a correct leveld bed? I unleveld it and later when i am at home i will see if ut works again with unleveld bed.

@gr5

[DidierKlein 729]

If it skips on the first layer then maybe your bed is to close. This would explain why it works with an unleveled bed (assuming it's not to far from the nozzle, so quite leveled)

[diettelo 5]

It skips only later when speed up with a leveld bed unleved it does work.

I leveld with 0.1 mm metal feeler gauge

[diettelo 5]

I think i found the Error lol. May this also can cause a Skip Back?

I replace it and bed level

[DidierKlein 729]

It could block the bearing or something like that so indeed replacing that piece would be a good idea