Is this normal?

[JAZZCNC]

You have to remember these are rotary axis, not lathe's so the runout will hardly be noticeable for the majority of work and if you require higher precision then you either use 4 jaw chuck or use soft jaws and bore them as MC suggested. The pulley runout is of no concern whatsoever in this application.

[A_Camera]

You have to remember these are rotary axis, not lathe's so the runout will hardly be noticeable for the majority of work and if you require higher precision then you either use 4 jaw chuck or use soft jaws and bore them as MC suggested. The pulley runout is of no concern whatsoever in this application.

This is a 4-jaw chuck... which is why I expected higher precision, but sure, I understand that for most things this error will not make a difference.

[magicniner]

4 Jaw INDEPENDENT chucks give better precision than 3 jaw chucks because each jaw is adjusted INDEPENDENTLY.
What you have is a 4 jaw scroll chuck with nothing to give you better precision than a 3 jaw scroll chuck.
You can get scroll chucks to meet your expectations but expect to spend a lot of money, more than you expect!

[A_Camera]

Yes, I understand the independent chuck jaws can give good precision because each jaw can be adjusted individually, that's obvious. But it also means a lot of extra time before the work piece starts spinning. Anyway, it looks like that I could get MUCH bigger and better precision by just cleaning the surfaces.

[mekanik]

I seem to recall you can get 3 jaw chucks that have adjustment in the backplate, you put a short mandrel in the jaws and dial out the runout then lock it.

Regards
Mike

[m_c]

I seem to recall you can get 3 jaw chucks that have adjustment in the backplate, you put a short mandrel in the jaws and dial out the runout then lock it.

Regards
Mike

I don't think I've ever seen a scroll chuck with that kind of adjustment, but I have seen collet chucks with that kind of setup.

I should have said independent 4 jaw in my original post, but Magicniner has already clarified that.

You can improve accuracy by grinding/boring the jaws (remember you need to clamp them onto something near the correct size first, to preload them, and standard jaws are generally hardened to some extent), but as I mentioned, that accuracy is likely to vary over the scroll. Scrolls are rarely a precision component, and accuracy varies over the scroll.