Did this on my CJ18A "taper rollers" did not fit the shaft difference in dimensions damaged the shaft, plus seals are a problem
this cost me a new shaft, so went with angular contact bearings
Looking back i think the original bearings where just as good
Shame I did not hear of this earlier.....
Ben, the spindle on the mini mill/lathe is designed for standard ball races, and as such are an interference fit on the shaft and housing.
Taper rollers are designed for a slidibg fit on a shaft with an interference fit in housing.
When I change both of my machines to tr bearings, I used wet n dry paper to polish the spindles for a tight sliding fit of the inner races to ensure the bearings would preload on assembly.