Mpc repair - how round can you get it?

[Bach5G]

I received a mpc today - used - and the shank is an little out of round.

How much can you get back into round?

[Burgerbob]

Totally depends. Sometimes you can't tell, sometimes it's never right again.

[ithinknot]

You can get it pretty close to perfect, but not with just "the tool". The collars that Instrument Innovations sell are a good way for the band director to avoid overshooting and flaring the end, but if you're trying harder it's more a case of using loose mandrels and working the high spots from the outside.

If the backbore ends with a single taper, with a flat edge to the shank end, then you can usually get it very very close. It's harder to camouflage the exterior damage when there's an extra chamfer/countersink at the backbore exit.

The original damage is almost always repairable... other people's repair attempts, less so.

[ghmerrill]

^^^
This.

You have to remember that it's not a true cylinder you're dealing with. That makes it harder. And the chamfer/countersink issue may be ultimately insurmountable -- even with a lot more equipment than you're unlikely to see outside a real machine shop. Even then, ... I have one where I've decided "close enough is good enough".