Just can't get Smooth Surfaces

Okay, I feel like I must just be doing something wrong.

I’m using a Lulzbot Mini with Black HIPS 3MM Filament and Cura 18.03 Software.
I just don’t seem to be able to get smooth models. Attached is typically what I am getting. And this one was at 0.15 layer hight and print speed of 25.

I’ve tried tons of adjustments, even different models. I’ve exported .stl models from Solidworks on the PC and Strata 3D on the Mac (with slightly better results from Strata). I’m still getting this kind of ridged, cruddy surface. Is this a result of the machine (nozzle size, filament) or of the software, (speed, layer height) or the model?

Any ideas are appreciated.

In that photo, the model has a domed top and due to the layer height you used, the layers are visible. Try a lower layer height. And it seems as you are over extruding a bit.

Well I’m at a layer height of .15, I suppose I could go down to .05 and try that.

How do I remedy over extrusion?

You’ll never get rid of the stepped look on a shallow domed surface with a FDM printer. To get it completely smooth, you’ll need to post process. Limonene I believe can dissolve and smooth HIPS.

The zits on the surface is a sign of over extrusion… calibrate your e-steps or lower the flow (%) parameter in Cura… found under the Filament section on the Basic tab (switch to full settings).