Skipping, Blobbing and Rough Prints

Tried searching, but couldn't find anything that matched exactly what I'm experiencing.

I don't think I changed anything since my first few prints (which were much better than I'm getting now), but I could be wrong. Now all of a sudden, I'm having issues with the following:

1. Skipping - the hotend will go quite far sometimes without actually laying down any ABS.
2. Blobbing - likely related to #1, the hotend will lay down a blob of ABS, followed by a line of ABS that fades off toward another skip
3. Rough Prints - likely related to both #1 and #2, my prints are coming out really rough, especially on the first few layers. It's almost as if excess ABS is collecting on the hotend and is leaving bits of extra ABS on the edges of each line.

Attachment 4011

This picture (sorry, hard to see red ABS on a red heat bed) shows #1 and #2...I'll have to run another print and try to get a pic of #3, assuming there's not an easy fix.

Any help is greatly appreciated.

Speaking to #2, it looks to me like something briefly catches and allows the pressure to build up in the hot end, and the extrusion tapers off as the pressure goes away.

Does the large gear rotate consistently as the circle is made? If not, make sure the small gear is tight on the motor shaft and that the large gear isn't binding up on the heads of the wheel bolts at the top of the x-carriage.

It that seems OK, make sure the filament spool isn't catching. Are you using the stock spool mount? Some people have had a problem with spools not smoothly rotating on it.

You might also pull open the guidler arm on the extruder and take a look at the grooves of the hobbed bolt with a flashlight. If you see any grooves with filament in them, disassembly of the extruder is warranted so you can properly clean out the grooves and try again.

EDIT: After that, I'd probably try taking the hot end apart to make sure there isn't a bit of metal stuck floating in the nozzle tip.

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Originally Posted by csader

Tried searching, but couldn't find anything that matched exactly what I'm experiencing.

I don't think I changed anything since my first few prints (which were much better than I'm getting now), but I could be wrong. Now all of a sudden, I'm having issues with the following:

1. Skipping - the hotend will go quite far sometimes without actually laying down any ABS.
2. Blobbing - likely related to #1, the hotend will lay down a blob of ABS, followed by a line of ABS that fades off toward another skip
3. Rough Prints - likely related to both #1 and #2, my prints are coming out really rough, especially on the first few layers. It's almost as if excess ABS is collecting on the hotend and is leaving bits of extra ABS on the edges of each line.

Attachment 4011

This picture (sorry, hard to see red ABS on a red heat bed) shows #1 and #2...I'll have to run another print and try to get a pic of #3, assuming there's not an easy fix.

Any help is greatly appreciated.

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Something else to consider, is your bed level? I had an issue last night that looks almost like what you have. My bed wasn't level anymore, the extruder nozzle was pressed down completely on the glass so no filament would come out, it was clogging up the nozzle and then once it went up on the Z axis it would come out in little skips and gooey blobs. Once I re-leveled everything was fine.

Thanks for the tips. I'll give these a shot and update...

Printing now and it seems to have been a bed leveling issue. I'll update if it turns out that's not the case.

My reasoning on this is not scientific at all, as I also cleaned the glass really well, so I suppose that could have been the issue.

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Originally Posted by csader

Printing now and it seems to have been a bed leveling issue. I'll update if it turns out that's not the case.

My reasoning on this is not scientific at all, as I also cleaned the glass really well, so I suppose that could have been the issue.

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Your picture is interesting. Those smears of plastic that fade to nothing usually signify that the nozzle is scraping the bed because it is too low. Usually I get this on half of my part if my nozzle is set too low and the bed is uneven but I have never seen it happen in an uneven pattern around a circle. Usually I would expect on half of the circle to show this low area and the other half higher. If this is the issue, maybe this picture is of several attempts at printing this circle with different bed adjustments per blob.

If not I would say there the hobbed bolt isn't grabbing the filament at the correct tension, the extruder gears are not meshing or moving without interference, or the filament has bumps or is not perfectly round.


When you say you cleaned the glass really well do you mean that there is no bed treatment on it?

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Originally Posted by gmay3

Your picture is interesting. Those smears of plastic that fade to nothing usually signify that the nozzle is scraping the bed because it is too low. Usually I get this on half of my part if my nozzle is set too low and the bed is uneven but I have never seen it happen in an uneven pattern around a circle. Usually I would expect on half of the circle to show this low area and the other half higher. If this is the issue, maybe this picture is of several attempts at printing this circle with different bed adjustments per blob.

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Interesting that you say that, as this uneven pattern is what made me ignore bed leveling as the issue initially. This picture was a single attempt at the print. However, now that I've leveled the bed (the nozzle was too close to the glass for a sheet of paper to slide with friction, possibly even touching) it's working much better.

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Originally Posted by gmay3

When you say you cleaned the glass really well do you mean that there is no bed treatment on it?

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I cleaned it well with soap and water, and reapplied a very thin layer of Washable Disappearing Purple glue stick. I had previously just been applying a new layer of glue between prints (max 3-4 prints before cleaning).

I would expect it to be to close all the way around so it would just build up and spit build up and spit.

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Originally Posted by bstag

I would expect it to be to close all the way around so it would just build up and spit build up and spit.

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Usually when my nozzle is close all the way around a print, nothing ever comes out. Instead, the hobbed bolt grinds a groove in the filament and the only way to fix it is to pull the filament out and clip off the grinded down portion. A blast of canned air is also helpful to blow out all the ground plastic, especially out of the hobbed bolt teeth.

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Originally Posted by gmay3

Usually when my nozzle is close all the way around a print, nothing ever comes out. Instead, the hobbed bolt grinds a groove in the filament and the only way to fix it is to pull the filament out and clip off the grinded down portion.

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That's what typically happens to me as well. There are a few variables though.

1) If there's any play in the nozzle (hot end loose in the extruder, X-carriage not tight on the rails, etc.), it might be possible for the extrusion to vary as pressure builds and pushes the hot end up. It's easy enough to check for this - raise the carriage up and see if there's play when you try to move the nozzle around. I remember going back through my extruder assembly to eliminate some play mine had.

2) I've had problems start appearing after applying multiple layers of the glue stick. It builds up pretty fast, and it's fair to assume the print surface can get uneven really easy since it's hard to hold the stick exactly perpendicular to the surface. Now I mainly reuse the same glue layer a few times and then clean it off and apply a fresh layer. In a pinch, I'll wetten the surface and reapply some glue, but I think that starts to pull fibers out of the paper towels I use since that seems to not hold as well.

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Originally Posted by printbus

That's what typically happens to me as well. There are a few variables though.

1) If there's any play in the nozzle (hot end loose in the extruder, X-carriage not tight on the rails, etc.), it might be possible for the extrusion to vary as pressure builds and pushes the hot end up. It's easy enough to check for this - raise the carriage up and see if there's play when you try to move the nozzle around. I remember going back through my extruder assembly to eliminate some play mine had.

2) I've had problems start appearing after applying multiple layers of the glue stick. It builds up pretty fast, and it's fair to assume the print surface can get uneven really easy since it's hard to hold the stick exactly perpendicular to the surface. Now I mainly reuse the same glue layer a few times and then clean it off and apply a fresh layer. In a pinch, I'll wetten the surface and reapply some glue, but I think that starts to pull fibers out of the paper towels I use since that seems to not hold as well.

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Yep, checked tonight and #1 was seriously an issue for me. X-carriage wheels were loose, and so was my bed. Tightened everything up using the eccentric spacers. We'll see how the next few prints go.