Bravo!
I just started doing something similar.
Only I chose a ER11 C8 L100 spindle. When I got the bearings, I discovered why the spindle was so cheap! The shaft is not parallel. The spindle falls into the bearing with no effort at all. 8.00mm at collet end to 7.93mm over the length.
These spindles must be quality rejects. Thank God for adhesive!!.

I found a bloke in New York who makes spindles for PCB mill & drill. http://cnconabudget.com
You'll find detailed photos of the parts -- makes reverse engineering so easy.....

:-)