Tubes not getting enough filament?

[JustinDeming]

I've asked about this once before with a less obvious example, but this time I hope the problem is quite apparent.

The central tube in this waterwheel model has way less filament in the outer reaches of the central tube than the inner are of the tube.

My theory is that instead of extruding enough for the distance around the tube, it's extruding enough for the distance across it. Either way, the outside of the tube looks terrible, and I can't imagine a setting I'm getting wrong that would cause this. If you look carefully there are four half columns around the large circle that are also beginning to display this, with a kind of candy cane structure.

I printed this on a MendelMax 3.0 printer, .15 mm layer height. I've had similar problems with other models, but this is the most extreme example I have. I hope to print many of these, But I need to find a solution to this problem.

[CompoundCarl]

That can very easily be caused by bad retraction/coasting/wiping settings. They all will have a large affect on something like that, and as the feature gets smaller, it will become more obvious if you don't have those settings perfectly right. So I'm not surprised that it's the tiny area that's showing the issues.

If you want to post your factory file, perhaps others can take a look and make some recommendations