Hello Jean. Welcome to the Zone!
Maybe this will be helpful:
My lathe chuck ( jaws ) have a eccentricity of 0,004". I would like to correct this problem. What is the better way to correct and how can I do that? I would like to grind the jaws.
or a boring bar works for me. It's a common problem with a scroll chuck. The scroll on cheap chucks isn't very precision, machine the jaws for one diameter and they will run perfectly true, open up to a larger diameter and they will probaby run out again.
5c collets are much more precision and give a much better grip on the material, yet have a smaller thru bore(in most cases) and require changing between hex stock, round stock and diffrent diameters.
Welcome to the wonderful world of precision machining!
We use softjaws on our scroll chucks. Indicate the chuck in round, chuck on something to put tension on the masters, and start tooling out the jaws. We run lots of molds, and if the jaws are tooled right they will run true everytime. We often tool out several diff. diameters on one set of jaws so you dont have to change jaws all the time. A good scroll chuck always helps.