I have fitted a few of the Chinese 5C collet chucks.
The runout on the last one, fitted about 3 months ago was 0.008", and I have had worse than that.
They do look great, all ground up or chemi blacked, but that is all cosmetic, and people think that because they look good, they must be good. Far from it.
After getting the backplate machined up perfectly and the chuck fitted, I just mount up the toolpost grinder and everything is ground up to true within a few minutes.
You only get what you pay for. 100 UKP for a cheapo 5C chuck that has to be put right, or 400 UKP for a quality one that runs true from the off.
I have now decided it is easier to make my own ER collet chucks. You can then guarantee they are true to begin with. Just buy the collets and closer nut.
I know everyone won't have the facilities I have, so until you do, you will need to beg steal or borrow the bits needed to put them right.
If you have purchased one of these ER chucks, there is a way that you can use basic machinery to get them running true.
The attached C-o-C shows what is needed.
The stub in your chuck is machined up and NOT touched until the operation is of flange skimming is complete.
The recess and flange might only require a couple of thou to be skimmed off, but it must be done with razor sharp tooling, preferrably HSS.
Then machine up your backplate for a snug fit.
Unless you have grinding equipment, this is about the easiest way to true it all up.
I have used this method to true up 3 jaw chucks to have a max of 0.0002" runout.
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