text -
I cut a ring into 3 equal segments and placed them between the jaws so that the jaws could be tightened against the segments which mimics the compression when the jaws are tightened on a bar. The jaws can then be ground in situ with a toolpost grinder using a grindstone or diamond coated burr etc, while running the lathe. If you do not have a toolpost grinder you can just mount the burr in the toolpost. This worked for me, my old three jaw chuck is concentric to .001"/.002".