Small cutters really need much better than a thou TIR. Better than a tenth would be much more suitable. Otherwise the necessary low chip load per tooth will leave you cutting on one flute only. A decent level of precision in the bearings is called for, together with good adjustment for preload. No-name deep grove bearings of unknown class may not get you there. The other killer will be the concentricity of the spindle taper with the bearings seats.

Get these two points right and you are on a winner. Get them wrong an it's going to be a so-so spindle.

Just some thoughts
PHil

PS: I haven't read the whole thread so if I missed something sorry.

Quote Originally Posted by Jeremy View Post
So far I think I'm on-track to have a fairly solid little spindle with relatively good accuracy, probably better than a thou TIR.

Jeremy