I have been running my diy cnc mill spinde at full speed (3500 rpm ish) and it is getting excessively hot (ie too hot to touch for more than 5 seconds). The bearings are cheap taper rollers with a 1 " bore and I have tried oiling them with light oil and standard wheel bearing grease but are as hot in both cases. I did cheap out on the taper rollers as they are for trailer wheels and so I am not expecting super precision, however looking at similiar size cheepo TR bearings on the net the limit is 7800rpm with grease. They have a rubber seal on the outboard bearing and I have used this to seal the lower one. The top one is sealed using a close running 'labyrinth' but both are getting too hot. I have tried various preloads including as close to none as I could get but it does not seem to make any difference.

The bearings I have used are:
http://cgi.ebay.co.uk/2-X-L44643-446...item2eabddd0c5

Does this sound like a bearing problem, bearing misalignment problem or lubrication issue? I am not aiming for super precision but usable would be nice! The spindle in the workshop series of books 'Spinles' book uses similiar automotive bearings.

Thoughts appreciated.