Notice the wave?
What could have caused this, and how do I fix it?
It was very prominent only on one side…
Which printer? It looks like z wobble.
First pic, the striations make it look like z wobble, but second pic shows the waves are vertical so my guess is x or y belt issue depending on orientation.
The horizontal line wave distance in the left photo lengthens as it goes up - that part might be due to heat bed thermal cycling. It might be worth redoing the heat bed PID tune.
This can also be caused by the infill touching the outer wall of the part, deforming the plastic ever so slightly.
Delta or Cartesian printer?
Slic3r 1.29?
I’m going with heat fluctuation. If the banding was evenly spaced, like every 8mm,I would say z wobble.
Can be z wobble and heatbed flex/bend as I had. Try a print with lower bed temp (other material) or without. If its not there without bedtemp set then your bed is flexing. If still there then you have z wobble or too little z motor current
Looks like you have more than one thing going on there. Platform temp fluctuation (as mentioned by several people) is a likely one. Spool tension may also be at play.
More possible causes to check here: https://www.evernote.com/l/ANNwHDbE3dVGaaSClT2JJMcdHvmSmIKVSHw
Or one last suggestion… Inconsistent mix on the spool.
@Rodrigo_Chandia
It’s a custom built WeldingRod Bot.
Find it in thingiverse.
@Steven_Critchfield , I’ll check my X and Y belts. I’m also guessing that maybe they’re too tight.
I don’t understand why it works change pitch as it goes up… That’s weird.
@Jeff_DeMaagd , No heatbed was used. I printed this in PLA at 200Deg
@Peter_Willard , Sliced with the latest version of CURA.
I’ll check spool tension as well.
I’ll report back later in the weekend…
How stable is the hot end temp. I am seeing color variations which in PLA can result in changes in surface gloss from temp variations. Also look at the geometry. You see changes in the period of the banding as a relationship of layer time (areas with more cross sectional area seem to have different banding frequency vertically).
I would start with PID tuning for rock stable temps, then move to looking into your part cooling, then finally into your spool tension. Your printer also looks to be a Bowden. Bowden can be more susceptible to hot end temp variations because back pressure really affects filament feed performance which can yield extrusion variations that become visible in Z.
@Eclsnowman , that is really insightful, I didn’t consider Hotend temp variations, and that makes sense as to why banding went less towards the top, the part had more Infill and more detail towards the bottom.
I’ll give your suggestions a go on Monday 
Acceleration settings reduce.
I mean. Check the. Acceleration settings. If it’s high then reduce. It