meow2222 wrote:
If you have no sharpening equipment, even an angle grinder can do it,
provided you use very light pressure only, and take frequent rests to
avoid overheating the bit. With practice a bit can be reground in a
minute this way.

I'm not that keen on this idea - yes, I know it can be done, but there
are people who haven't the *faintest* idea, who will try it. I watched
an assistant in B&Q on Sunday morning (needed tap washers, so had to
go there, unfortunately) advising a chap there with his 3 small boys
in tow. The bloke was clueless about what he wanted, or how the things
work, or what materials they cut, with what wheel, etc. etc. You get
the picture. Him, sharpening a bit on an angle grinder? I hope not!