I have a TEVO Tarantula, with modified extruder and hot end, which is capable of producing really excellent quality prints. But I'm finding for certain kinds of features, the g-code being created by Cura gives really terrible results, and don't know why.
Here is a link to the Fusion360 model for my current part: https://a360.co/2Ts9cBH
Note that the model consists of three different cross-sections:
Bottom "plate", 1mm thick. This prints perfectly.
Lower profile, ~4mm thick, which consists of two concentric rings, each 0.040" wide, with a 0.040" gap between them. This prints perfectly.
Upper profile, same as lower profile, but with several segments of the two concentric rings removed. This prints horribly.
The bottom "plate" and "lower profile" both print 100% perfectly, every time. They are very solid, excellent adhesion between layers, and dimensionally dead-nuts accurate. The upper profile is a complete mess. Surface finish is awful, and looks like too much plastic was extruded, at too high a temperature, with no more than ~50% fill. This whole area is very weak, and very ugly.
I'm sure this is a matter of settings, but I've been unable to find any that make a substantial difference in quality. It appears to me the problem is in the way it forms the walls. On the lower profile, it does mostly nice, concentric inner and outer walls, then a single line right down the middle between those two walls. On the upper profile, it alternates between a single line down the middle, and lots of very thin, parallel diagonal lines jammed between the two walls.
The g-code file is attached. The problem area starts at layer 25, on line 25519 in the g-code file. This is being done using the "normal" profile.
Normal.gcode