Ironing and surface scars

I’m using cura-lulzbot 3.2.21 with my TAZ6 (Aerostruder if that makes any difference) and having real problems with ironing when the to-be-ironed surface is not the top layer.

For example:

The top part has a superb surface finish with ironing (it actually looks better in the flesh than in the photo as it’s only 65mm long) but the second part, featuring 0.3mm raised letters, has nasty scars on the ironed layer.

I’ve tried just about all the settings I can think of (z-hop enabled, z-hop on retract, retract on layer change, combing off) but I
just can’t stop the scars.

I even tried insetting the text by -0.3mm and get the same sort of result :frowning:

Does anyone have any suggestions/comments/ideas?


Based on the way those lumps in the surface are forming (extending from the lettering) I kind of wonder if the model itself needs a small adjustment. A lot of times when I see surfaces like that on my models it is because I need to go back and flatten the surface of the model as there are small almost imperceptible changes in the layer that are then exacerbated in the final print.

Thanks for the suggestion.

The model was drawn in Fusion 360 so the original surfaces should all be square to the X/Y plane. I do see Fusion create some strange triangles when converting to STL:

which are definately there in the mesh as viewed in meshlab:

However, the artifacts don’t line up with these and do seem to be down to Cura’s ironing strategy. Here’s a screen scrape of the GCode Viewer in Octoprint while the ironing layer is happening (part way through):

You can see that it’s ironing in sections around the letters rather than ironing the whole layer as it does when there’s no lettering and the artifacts seem to be joins in these ironed sections.

As a comparison, here’s a couple of prints. The top sliced by KISSlicer and the bottom by Cura (same stl used for both). KISSlicer doesn’t have ironing so the flat area around the letters isn’t as nice as it could be in Cura if Cura’s ironing coped better.

Tis a shame as without the lettering, Cura’s ironed top layer is really really nice.

Any other suggestions most gratefully received.