UM2+ Under Extrusion

I've been having a lot of problems with under extrusion on larger prints. After inches of height I'll get some bands of poorly adhered fine stands before it goes back to normal.

I've been tinkering with temperature and feeder speed percentages and nothing is properly solving the problem. I had been printing some simple models in PLA at 60mm/s but perhaps it's over optimistic for that to work on every print. Slowing it down to 50mm/s has helped but I'd like to try to keep the speed up by making other adjustments, if I can.

Today I was printing in white and I noticed how many evenly spaced partial grinding marks there are on the filament.
My best guess from what I have read on the Internet is that these are likely to be caused by retraction being too frequent.

Filament Feeder Tension

As I'm mid print it is tricky to adjust retraction settings so I'm going to fiddle with the feeder tension.
This is on an Ultimaker 2+ so they come pre-set and are not supposed to need adjustment from the centre.

- One turn 

As it is only minor grinding, I've twisted the adjustment screw by one full turn clockwise. That is less pressure on the filament. The indicator moves up a tiny fraction away from the centre.

- Another turn

That's better but I still think the marks on the filament are too deep.
I'll try another turn.

From what I've read on forums and on Ultimaker's web site, if the filament is misshapen too much by the feeder it can either get stuck in the Bowden tube or in the hot end. Probably gets stuck at the isolator.

- One more turn for luck

I'm now three full clockwise turns off of centre and the marks on the filament are cleaners, showing just the even knurling and none of the grinding.

Reluctantly I've also reduced the speed of the print and at last I appear to be getting better layer adhesion.

I'm printing at 26% infill so I don't think that helps. At 30mm/s it's now feeding better.

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Update: 1 August 2017

I spoke too soon. I was still getting under-extrusion just not for the same reason.

I'm fairly sure that the friction as the filament gets closer to the centre of the reel is still the cause of intermittent poor layer quality. I can either go back to using only cut lengths of filament, which is what I've done for years or I can use bearings for the the guides, axles or stands, as others do.

I'll have a look at what's available.

...

I fixed this by using bearings, see my article:
http://blog.discoverthat.co.uk/2017/08/filament-spool-spindle.html


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