Truing MT3 spindle bore on a mini lathe?

[gmm22]

Can this be done?

My new mini lathe registers .0005". I'm not sure how this compares or if it is acceptable.

[dewat]

I bought some 3MT collets from Little Machine Shop, thinking that using them in the spindle would be as accurate as possible but they're still out about .0005.

For what I do its in the ball park if I need it dead on I use the 4 jaw.

[GadgetBuilder]

My 7x12 also has a half thou runout in the MT3 bore, which I suspect is typical.

The spindle flange used to register the chuck is much better, about a tenth so it is the way the MT3 bore is machined rather than a bearing problem on my machine. My guess is they machine the spindle, mount it on the lathe, then true it in place to get lower runout on this register.

Improving the MT3 runout would need a taper attachment, something I built but haven't had the courage to use on the spindle. Chatter could easily be a problem with the long overhang needed here. In addition, an MT3 reamer would be helpful to get a good finish after machining and these are expensive for a one-use tool.

I mark everything I mount in or on the spindle -- doesn't reduce the error but at least I make consistent errors