How about sharpening hole punches?
I have an old Greenlee 2.75" punch that I've used for 30 years to pop out those common, old buzzard 3" round meter holes. It's gotten to the point where I needed an extension pipe to make it turn and cut through. Dull, after going thru countless steel and aluminum panels..
I brought it to a metal shop and they waved it off, saying it was difficult to sharpen without ruining it. A friend tried to sharpen it and it appears to be ruined - doesn't cut thru anymore... sigh. I guess once a little metal is removed from one of two halves, the tight fit is gone and it doesn't work well.
This is the one - goes for about $220 now. I paid $40 back in 1972... :-)http://www.all-spec.com/products/730BB234.html
Anyone have ideas on this?