Funny, when i got on here last year i posted a couple times mentioning 4J chucks which i use outboard, and sometimes inboard. Mostly got comments about how much time i was probably wasting.
As far as grinding jaws on a 3J, the guy who mentioned finding the nominating pinion is spot on. After that, on a worn chuck, grinding (or boring top jaws) will work in one aproximate opening. Seldom the same thoughout the scroll range it there are a lot of hours on the chuck.
For cue work, i'd just use top jaws and bore occasionally.
But i prefer (& use) high end adjus-tru style chucks on the front. Only one pinion, so no mix up. Then adjust the run out with the adjus-tru screws around the rim, if/when needed for a given job. More or less a scroll chuck that can be adjusted/centered like a 4J when needed.
If you make your own backplates, most 3J's can be converted to adjus-tru feature. But if it is a cheap import, the scroll will never repeat because they are built too sloppy internally. (Usually good machining/grinding, but too loose a fit, & not take-up provision). So converting a cheap 3J might or might not yield faster routine set up than a 4J.
smt