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I'm printing a few very simple monitor support stands and I noticed something odd while printing. In the STL, the outer wall of the part is perfectly smooth (but at a small angle).

However during the print, you can see a pattern form. It's faint, and on a finished print you can barely feel it with your hand, but it is there.

Here's a snapshot of an in-progress print. You can see it most clearly on the right-hand part - long, vertical triangles on what should be a smooth surface.
What could cause that? I can think of either 2 likely candidates: either the slicer, or delta math. So far I've only tried MatterSlice with this particular part, and I haven't noticed it before. (I've traditionally used RH/Cura but I recently switched to MC/MS.)

However I've printed this particular part multiple times and it seems that the exact position of the triangles depends on the part's position on the bed, so I suspect delta math.

This isn't something that I feel needs fixed, I'm just asking for curiosity's sake. Of course if there's an easy solution, I'm all ears.

I'll post the STL file too just so we can be sure this isn't a problem with the model.

On second thought! Could that possibly be the infill overlap interfering with the perimeter? My infill is set to triangles, and since the wall is at an angle, it makes sense that with each layer, it would intersect the infill pattern at a slightly different position each time...

That's actually exactly what I was going to suggest. I have the same happening on some of my models, but it's only really apparent across a curving surface. The only reason it was made so apparent to me is because I have a tendency to use translucent colored filaments.

Yep, the more I think about it, the more that makes sense. Thanks for weighing in on it - case closed!

Only fix I can offer/suggest is to increase the number of perimeter walls you print. As long as your printer is calibrated well, more walls should minimize the effect seen on the outer shell.

Just saw this posting so sorry for the lateness.
I have found that reducing the amount the infill overlaps with the perimeter can really help minimize this effect, especially when you have only 2 or 3 perimeters. You just need to be careful not to reduce the overlap such that the infill isn't well fused with the perimeter.
In MatterControl this setting can be found under Print/Infill with "advanced" turned on.