Quote Originally Posted by Tenson View Post
What is involved in converting my ER16 2.2KW spindle to an ER20 type?
It's basically not realistic. Since the ER20 taper is bigger than the ER16 you would have to get a new spindle shaft made, which is going to cost a huge amount.
Some sort of 10mm to 1/2" adapter would work, but you would have to be very careful on how big a cut you take with that as it wont be very strong unless supported by another bearing.