It’s the fact I was a toolmaker for 20 years and am used to working with precision tools/equipment. I no longer have access to anything like that so I’ll have to use a “flap wheel” and the thought of that is very unsettling.
I've done a couple of them.
The first, on the Grub, I eyeballed it, taking off a little at a time until it just started into the hole. It pressed in with some resistance, so I think I got it right.
The second was for Graywolfs02. We measured the difference between the old and new cups, and enlarged the hole by that amount. Same result.