Bearing arrangement for a high speed spindle

[charkmandler]

My son has asked me to build a high speed spindle for milling miniature electronic components. Requirements are;
The milling cutters will be 1mm dia at the most and less, for milling circuit boards and miniature components.
Very light loads - cuts down to 0.1mm
Speed requirement will be 10,000 rpm and above.
Zero runout in the spindle set up.
He has bought an ER8 collet chuck with with a 4 1/2” 6mm shank - the 6mm ID of the bearing limits choice of bearings
This is not for commercial use so will not be running for long periods.

Looking into the bearing arrangement the best way seems to be to use two sealed angular contact bearings back to back (cutter end of the spindle) and a ‘floating’ bearing at the other end. This will eliminate any play and take into account any expansion. Unfortunately the cheapest price we can find for these bearings is around £160 and is too expensive and it is impossible to find ones with a 6mm ID.

The Quorn arrangement with spring preload on the bearings was my initial consideration although I'm not sure how it would cope with the speed.

A possible alternative is to buy some taper bearings and pre load them. I have not checked out price and the other issue is they will need to run in oil - would a labyrinth seal remain oil tight in a vertical position?

Does anyone have any suggestions?

Thanks, Mark.

[Magicniner]

You are massively over thinking and over complicating the job.
If you'd gone for ER11 on a 10mm shank you'd have a massive choice of bearings, just use twin sealed ball races at the nose and one floating in the housing at the pulley drive end, it works fine for micro-milling down to fractional mm cutters.
I've been running the above arrangement at 30000rpm for several years with 30 hours or so total run time, took me an afternoon to build and cost me £15 plus the ER11 chuck and the Aluminium for the body and pulley, I drive it with a length of round Polyurethane belt cut to length and welded with the help of a disposable lighter.

[charkmandler]

Thanks Magicniner, my son had already bought the ER8 so that greatly limited bearing options as you say. Reading the bearing specs on ball races the runout seemed too much but if its working ok for you I will follow your lead. Nice and cheap as well.

[Magicniner]

Thanks Magicniner, my son had already bought the ER8 so that greatly limited bearing options as you say. Reading the bearing specs on ball races the runout seemed too much but if its working ok for you I will follow your lead. Nice and cheap as well.

Talk to your bearing supplier, I always drop into the trade counter and discuss my needs, the bearings I bought were high quality industrial application 30,000 rpm rated units, not "skateboard wheel" stuff by any measure!