Run out of 3-jaws chuck

Normally, no one will re-chuck the work piece to turn both ends, unless it is absolutely necessary. Especially re-chucking the 3-jaws self centering chuck will make you get into trouble.

But, checking the run out is another thing; it can be performing very easily.
I am going to use an edge finder to check the run out. Some people will use a drill rod, or the clamping end of the drill bit. All of them are work, as long as the testing rods are straight and concentric.





Because the chuck was sitting on the spindle shoulder, if you didn’t check the flatness of the shoulder, you can put the probe closer to the chuck to eliminate the whirling effect.

If the testing rod has marking on it, it’s better to avoid clamping and touching on the marking.

I was surprised that my chuck has 48 microns run out. It was a bit large. What I can do now is dissemble and clean it; to see if I can make it better or not.

3-jaws self centering chuck was dissembled and cleaned

Re- grease the chuck

Assemble the chuck

Finally, I’ve got 13 microns run out; it’s a much reasonable result!
Run out of 3-jaws self centering chuck can be varying to different chucking diameters duel to the structure of the chuck.

My suggestion is after you’ve confirmed the center of spindle was parallel to the X rail; you can turn a shock down to the common working diameter of your projects, cut off it from the chuck, and you will have your own run out testing rod.