when I run an operation that mills a face down on my CNC, it leaves this weird texture. It's hard to describe, so I attached an image. What is it caused by and how do I fix it?
No milling operation will give you a perfectly flat surface. The level of finish you can achieve will depend on the capabilities of the mill itself, the tooling you use and how the tool paths are set up.
Also when facing. Because you are cutting with a rotating face you will inevitably have one side of the tool moving int other direction of travel and the other side moving away from it which can cause slight variation in finish from one side of the cut to the other.
Generally finishing operations use higher cutting speeds and shallower depths of cut than roughing operations.
Often milled parts need additional finishing processes if you want a very high level of cosmetic surface finish.
In this case probably the best and easiest option is to rub it down with a sanding block.