Hello. I’ve recently started 3D printing with my Prusa i3 MK2, and have been getting good prints off of it. There are a couple of issues that I don’t quite know how to fix. As seen in one of the images, there is a tiny, tiny gap between filament lines in the final layer of the print. Is this underextrusion? The other picture has me a little more confused. There appears to be tiny imperfections, usually along the same vertical axis, which makes me think that this is a mechanical problem.

Are these issues that are fixable? Or are they just par for the course in FDM printing? Thanks.


Forgot to add the images:




The first item is quite OK for desktop FDM printer (in our opinion). The second, you could adjust retraction settings.

Hello Mathew

which silcer, what material, what temperature, what layer height, how many top layers, how many walls etc.? There are a lot of settings in the slicer software which could be causing this, I am not thinking that there is a mechanical problem. In the end it could also be underextrusion. Is the tensioning bearing which presses the filament against the filament feeding gear tight enough? That’s one mechanical adjustment that comes to mind. If you are printing at very high speeds perhaps the extruder can’t keep up…

In the different slicing softwares there are a lot of settings e.g. letting you change the order of infill and perimeter printing and also retraction / head lifting options etc. Play with these parameters to get rid of the blobs, play with extrusion rate / temp / speed / nozzle width and other overlap functions in the software to get a smooth finish. Also the material is an issue, some lay down nicely some not so much.

I had a problem with infill not attaching to perimeters at the beginning and there was some options both in Slic3r and Cura for increasing the overlap between perimeter and infill. Remember if you use Cura that there is a TON of options that are not visible by default and you can get the to show by activating them in setup.

Did you build your printer yourself from a kit?

Happy printing and good luck!



I have seen this effect using a filament that needed to be extruded at a higher temp. It lools like there’s not enough melting going on between adjacent lines.

Hope this helps


First image shows an under extruded top layer.

1. Make sure that your extruder is calibrated (so that you’re using the correct extrusion multiplier)

2. Print with more top layers
3. If you cant/dont want to print more top layers, in for example Slic3er you can set the top layer to over extrude a bit.

Last image, typical “blobs/zits” that you’ll never get rid of (kind of), if you’re using Simplify 3D, that looks more like Slic3r blobs though, and if you set the seam positon to random they will spread out more. If you have other issues with stringing etc, you can also adjust your Retraction settings some… but its pretty difficult to get rid of the blobs totally.

If you have more Prusa MK2 related questions I recommend the Prusa MK2 slack group that we’ve started, you can enter here: http://codehemi.com/

best Regards Patrik

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I built it myself. I am using Cura at default settings, 0.2mm layer height. 200/60 degrees. I’m fairly sure there are three perimeters. Ill definitely play with some of these settings in my free time. The filament feeder is working properly, and I’m printing at the default speed.

IMHO the default speed in Cura for the Prusa i3Mk2 is a bit “optimistic” I tend to print a bit slower. I don’t like the vibrations the machine makes at high speed…

Happy printing!

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1st pic : under extrusion. Increase the extrusion width or calibrate the extruder better. Also depends on the material you’re printing with (i.e.if you find the sweet spot with PLA, that may not be the same for PETG, etc.)

2nd pic : bubbles are formed as the hotend is going up one layer on the Z axis before starting a new layer (it stays a bit too long at almost the same place, hence it starts leaking). On some slicers, you can randomize the location, choose the location to be the fastest path (usually the default) or force it to be the closest to a give (x,y) points (so you can pick up a hidden place your object geometry) . However I don’t know if Cura has these options. You could also try forcing retraction between layers (again if your slicer allows it or if you’re a GCODE artist :))

[Edit] Forgot to mention as a solution to issue #2 : twick your Coasting settings in your slicer if it’s available

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+1 for underextrusion on pic one. Measure your filament, it may be on the thin side, and tell your slicer the actual thickness. Or increase extrusion multiplier a little.

2nd pic, the regular pattern you see on the curved surface looks like infill poking through. You need more perimeter layers to get rid of that.


Try printing one of the PLA models that came on the SD card pre-sliced. How does that look compared to what you’re getting? For example, print the Marvin using your settings, then print the Marvin that is already on the card. Granted it is more of a round object but the point is to see your settings vs. Prusa’s.