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Can extrude filament but can't print.

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When I manually move / feed material through the hot end It moves through flawlessly. Its been cleaned many times to make sure that stuff stuck inside clogging it is not the problem. Have stuck wire through and can see all the way through the hot end, and it moves material, but it can't print.

When it prints it starts and does the first layer alright, but quickly the extruder starts skipping and filament is not extruded.

I believe the ceramic in the hot end has some sort of bump on it which stops retracted filament from going through again. Do I have to replace the hot end? Is it possible to ream the ceramic to get rid of the bump?

any help would be great,


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If you have a UM2 and the extruder is skipping backwards it usually jsut means you are printing too cold or too hot but there are a dozen other causes.

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. Different colors print best at quite different temperatures and due to imperfect temp sensors, some printers print 10C cool so use these values as an initial starting guideline and if you are still underextruding try raising the temp. But don't go over 240C with PLA.

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>I believe the ceramic in the hot end has some

>sort of bump on it which stops retracted filament from going through again.

You would have to do about 20mm retraction for that to happen - I strongly doubt this is an issue. The typical 4.5mm retraction simply reduces pressure and doesn't actually retract down at the tip of the hot end. Most of the motion is happening in the bowden only.

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Even printing as slow as possible the filament will stop extruding or won't be able to start extruding. Have tested temps from 180 up to 250ºC and still it can extrude manually, but will not print.

Sorry forgot to say it is a Ultimaker 2, and I have 3 other Ultimaker 2's that are completely functional, its just this one giving problems. And this printer usually works wonderfully, but in the last couple of weeks it has had this problem.

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Is it possible that your filament broke into 2 pieces in the bowden? This has been a common problem in the last few months with brittle filament.

There is no ceramic part. There's the bowden which touches the white part which is teflon. Then that touches the heater block which is brass and is integrated with the nozzle. What country are you in? You can get the teflon part in USA at fbrc8.com (official utlimaker parts reseller) or my store (not official but cheaper) gr5.org/store.

You can definitely drill out the white teflon part. I have done this. You want a 1/8" drill bit. These teflon parts are not expensive though. By several. The newer UM2 printers come with some spare ones.

It's possible that you never get the filament past the white part or the next part but it seems unlikely.

Is your 3rd fan working in the back? If not this would cause the symptoms you see - the PLA softens due to retraction, enters cracks above and below the white teflon part. Then they cool enough to get stuck there and now the filament won't go up or down.

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