Sort of accidentally started a new build...

[McCreed]

That may have less to do with the tool and more to do with the discs you are using......

I'll second that.

As for holding the threaded sleeve, I made small clamping blocks out of pine to hold the sleeve in just a hobby vice.
Clamp the two blocks together, then drill a hole just smaller than the sleeve diameter centred right on the where the two blocks meet (like two halves of a mould).

This will hold the sleeve in a secure horizontal position without risk of squashing it out of round. You can make indentations in the blocks where the "nut" portion will sit, but I found the pine was soft enough to indent from the clamping pressure and not compress the nut.

I'm sure there is a proper name for this kind of "device" but I don't know what it is...