Thanks Tamra for the replies and the detail, that's useful.
I've bought a small diamond cup wheel specifically for this (I'll try it on the U3 spindle), but also have a grinder from my woodworking days - one side has a normal wheel, the other with a larger whetstone that runs in a water trough. To be honest I hardly ever used the whetstone as it was soooo slow... I thought the 'normal' side would maybe a bit too fierce, it is quite course for small items.
I'd rather drill than bore but have a cheapo made-in-China drill press that I have had for years. It's solid enough and has served me well but the spindle has a fair amount of play in it (it's on the list for examination and 'improvement' if possible). If I was aiming for a 13mm hole (to tap M14 to fit on the U3 spindle) I wouldn't want to go larger than 11mm on the drill press, and I'd bore the rest on the U3. Which is... kinda boring... ha ha.
They do say though that a tool ground to the correct angles is better than the indexable carbide insert tools (which I guess must be more of a 'one size fits all' option), so learning to sharpen generally is a good endeavour I think.
(The carbide insert boring bar has those trapezoid shaped cutting parts that fix with a tiny bolt, I don't know if you can sharpen those? I think they are just replaceable).
