High Speed Spindle

I have a homemade pcb drilling machine that I want to build a spindle
for. I bought a da300 collet extension and some collets for the sizes
I will need. The extension is .5 inches diameter on the body and
6.5 inches OAL. I purchased some 12mm X 18mm X 4mm teflon sealed
bearings rated up to 80,000 RPM. The ID is .4724 in decimal. I was
wondering if it would be worth while putting two bearings at the
collet end with a small preload on them and a single floating on the
pulley end? From VXB.com (just a customer) I got 10 for 19.95. Pretty
reasonable. I was wondering what the od should be where I mount the
bearings. Maybe .473? Was going to chuck it in my 4 jaw and use a die
grinder to turn it down as I am sure it is hardened. Had a dremel
before too much slop and tried a air grinder 1/8" 530000 rpm from HF
but it eats my 5 hp compressor for lunch. Hate to run a compressor 50%
on time just to drill .028 holes :>