Some time ago an unknown colleague had borrowed an end mill from me.

Have i had been there i would have stressed that it was aluminum specific cutter and that it should not be used on steel.
Unfortunately i was not and it did not occur to him to ask somebody who would have known better.

Next time i look into my drawer i see this.(first picture)

Now we have a tool and cutter grinder to sharpen the OD of an end mill, but chips were so big, i would have to grind off maybe 20 thou of the diameter on order to get rid of them.

Our TC grinder does not allow to re-flute end mills, so i had to do it holding end mill in my hands.

First i picked up correct angle, and then i slide end mill upwards, turning it at the same rate as to follow flutes.

It came out better than i thought.
I was not planing to use it for finishing anyway.

And it lost only 5 thou in diameter after this hack-regrinding.