@Quinc
Wack certain spots with a copper hammer... seen on the right of crank in pic. Sometimes when its really bad you pinch it in the vise. Sounds crazy but yes!
Ill try and break it down to the basics... Think of the crank pins and how they operate, you can have a crank webs off to one side so to the left or right and a lot of the time towards each other or away from each other. You use the dial indicator and measure run-out while you are spinning the crank on v blocks, by doing so you can see the hi and low points and can figure out if the web or webs need to be closed or opened.
If you wanted to close a web you would squeeze both of them together with what i prefer a vice, and tap it with a non maling hammer cause sometimes they get heavy AF!
If you wanted to open it i use a copper hammer to force it outward.
After all this, think of a straight edge, a long ruler. You want everything on that crank to spin in a straight line (very little run-out) !!
It sometimes takes quite awhile to get one trued up. especially triple cranks. If your really anal about it being perfect it could take awhile to get to .001 or less by going back and fourth beating the poop out of it for hours basically.
Hopefully i did ok explaining this, its how i look at it. Still learning everyday and its awesome. Its always changing, not all cranks are the same. Its literally alegebra. Problem solving!