Super rough top layers

The top layers of my parts, when flat or close to flat, are coming out looking very nasty. They have tall, sharp ridges, nearly a layer height thick.

This happens with both Lulzbot HIPS and some IC3D PLA. Using Cura at Normal speed.

Two things to try that have helped:

  1. Run in fine mode

  2. Experiment with part thickness.

For example, print a test piece that is .5mm, .75mm, 1mm, 1.1mm, 1.2mm, 1.3mm etc. Kinda looks like stair steps.

I think, like me, you’ll find the surface finish is dependant on these two things.

My best guess for #2 is because, for example, if your layer height is 0.18mm (ABS fine standard) and your top surface is, say, 0.9mm thick, you will get a smooth surface. Why? 0.9mm/0.18 = 5…nice and even. The last layer of material gets you to the 0.9mm requested.

Now, what if the top surface is 1.1mm thick?

1,1mm/0.18 = 6.1

Since lulz and cura can only operate in layers of 0.18mm thick (or whatever you set it for in expert mode), lulz will run an extra layer and smoosh it out (I think) and that’s what gives you some of that result. It’s the only way I can explain why different surface heights during the exact same print came out with different roughnesses in my testing.

(Theory subject to change as more data is collected)


When I see that on the top layer of a part, it is always over extrusion. Try dialing back your slicer’s extrusion multiplier a little and reprint.

I made a small half inch square about 10 layers thick. I print it at high infill to tweak the extrusion multiplier. If the top layer has gaps, increase extrusion a few percent. If the top layer looks plowed, decrease the extrusion multiplier a few percent . You should end up with a nice smooth top surface.

Also, measure your filament diameter with a micrometer or calipers and enter that value in your slicer software.

+1 on the over-extruding… try dialing back the flow multiplier as suggested… .9-.95 usually works well.

reducing the flow % helped a ton thanks for the tip as well as adjusting the layer height but in my opinion try the flow first because that worked a ton better for me