Strange blobs while printing

Hi everyone!

Have been printing fine for a good while now but lately I have begun to notice these strange blobs randomly on my prints. I have no idea why this keeps happening. It seems to be my nozzle extrudes too much filament at certain points for some reason. Has anyone seen this before? And if so, what was happening and what's the fix?

Looking forward to hearing people's experiences of this

Cheers

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Printsperation
Hi everyone!

Have been printing fine for a good while now but lately I have begun to notice these strange blobs randomly on my prints. I have no idea why this keeps happening. It seems to be my nozzle extrudes too much filament at certain points for some reason. Has anyone seen this before? And if so, what was happening and what's the fix?

Looking forward to hearing people's experiences of this

Cheers

It would be helpful if you can record a video of the print, but anyway here are my guesses:

1) hotend temperature problem, the hotend is heating up and therefore stops in position. this causes oozing and the blobs. you can check this by looking at the hotend temperature when the blob happens.

2) gcode problem, probably caused by bugs where the hotend stops in place and extrude. again, check this by looking at what the hotend does when the blob happens.

3) Printing using USB, the computer pauses for some reason, and the printer stops and a blob forms.


Try printing using an SD card.

I would second the possibility suggested by nebbian, however to overcome this possible issue, just minimise the host window after starting the print if using Pronterface

However I would put money on this issue being related to your extruders retract operation. Watch the gear wheel on the extruder and see if you can tell if it is moving equal angle of rotation on both the retract and unretract operation. I suspect the retract is failing/skipping steps and so when you unretract, it is pushing out some plastic

Please also list what electronics, slicer and firmware you are using, and also what sw you are using to send gcode to the printer. This will help a lot in giving a quick solution to your problem.

In any event this appears to be a simple to solve setup problem once we have the above info

Thanks for your feedback everyone! Knew the reprap community would be able to help me out!

Apologies for not supplying more info (silly of me). I have a prusa I3 with a hexagon all metal hotend with bulldog lite extruder (therefore can't really see internally to the gear wheel). I print off and SD and my prusa I3 uses ramps 1.4 and uses Marlin firmware. Cura is my slicer.

I will try another print tonight and record what happens. It is typically only within the first few layers (normally third to fifth I think).

I didn't realise the hotend will sit in position if it loses temp, that would make sense as to what is happening though! I will monitor this tonight and record what happens. If this was the case, how would I overcome this? The printer is only a few months old so can't imagine the thermistor has become faulty?

Thanks again for the help so far!

Hi again everyone. I have just quickly stuck a print on to record it. I have recorded it as a stop motion (1 frame every 0.5s) with the idea being that if the nozzle seems to stay in one position longer than that would show that the nozzle is stopping and that would explain what is going on. I have attached a quick video to show that this is not the case. But I am still getting blobs. The blobs seem to be mostly on the perimeter of circles if that helps? (edit... saying I can't attach anything larger than 614kb, so I will upload to vimeo and post a link)

Thanks again everyone