It’s kinda hard to see in the photos, but I’m wondering what causes these sort of circular, curve patterns?
You using a delta?
They’re tree rings, created by a lack of resolution of your printer’s x and y axis. Usually caused by flaky microstepping and mistuned stepper drivers.
It’s your slicer…
@Thomas_Sanladerer hit the nail on the head. Need to properly adjust your drivers so the microstepping is accurate.
I’m not sure what you mean by lack of resolution @Thomas_Sanladerer ?
Errors in microstepping and stepper tuning should result in distortion, correct? Fwiw, the output part is dimensionally correct (at least within the limits of my measuring tools), this effect is detectable only visually as far as I can tell.
I’ll try slicing it with Slic3r @Alan_Weber (this was done with Cura) and see if it changes.
@Jason_Gullickson what you’re seeing IS distortion. Those ridges, should probably have up to 10 different steps in between them. They jerk to the closest microstep they can achieve because of inaccurate current settings.
@Michael_Hohensee this is from a i2 Prusa Mendel.
By lack of resolution he means the polygon lines. As you know, if you had more polygons, you’d have a smoother piece. They don’t realize you mean the Moiré patterns that show up across layers.
@Alan_Weber By “circular, curve patterns” he’s not referring to the the polygonal vectors that run vertical on the ball. And no, we are referring to the moire…hence the “tree rings” moniker used to describe them.
@ThantiK I know. That’s what I said. Learn to read.
Dude, poor form.
Yeah there are hard edges there that are due to the limits of the model’s resolution, but yeah I’m talking about the circle you see as if looking at a tree ring from the top-down (I wanted to call it moiré but I wasn’t sure if that was correct 
I’ll check my stepper current, and I’ll also pay more attention to the orientation axis-wise when I remove the next one. It just seemed so regular, almost mathematical, that I wouldn’t have guesses it was something like dropped steps since when I’ve had them in the past they seemed intermittent.
I’ve heard of harmonic resonance problems with the triangle frame design that I thought might be involved, but I’ve never seen an example of that in person so I’m not sure what to compare it to.
These tree rings are just a natural consequence of slicing a round object into a Cartesian grid, right?
Exactly. Since your object consists of layers that are not infinitely small, you’ll have gridlines where one line meets another.
I think your printer is defective and you need another one.
@Jason_Gullickson I wouldn’t mess with your current settings. They seem mathematical because they are. They are an artifact of slicing. Tweak your printing settings and they’ll change… They’ll never completely go away though, they just get harder to see.
@Jason_Gullickson , What @Thomas_Sanladerer and @ThantiK are trying to explain is that your X and Y axes move in discrete steps. When you move diagonally, this creates a horizontal stair-step pattern, similar to the vertical layering effect. Like the layers, this effect is less noticeable when the steps are smaller, and this is called having a higher X/Y resolution. If, for example, you have 100 steps/mm on your X and Y axes, this is equivalent to having .001mm layers in those directions.
BUT if your steppers aren’t properly tuned for your motors (often because you or whoever sold you a kit chose bad motors for your supply voltage), they can stay on (or too close to) the full-step position too long, then jump quickly to the next full-step position. This effectively cuts your X/Y resolution down to what it would be without microstepping. so in the above example of .001mm horizontal resolution, if that is calculated with 1/16 microstepping, your print will actually look like it has .016mm layers on X and Y.