Sorby Spiraling cutter system

[Clarence Martinn]

About how many times can those cutters be sharpened , before they need to be replaced ?

[Richard Coers]

I you hone with a diamond file, hundreds of times. If you use a grinder, probably 75. If you grind it with a heavy hand, less than 20.

[Michael Mills]

1+ on what Richard said.
If you go to the Sorby site it tells (shows-video) you how to sharpen them.
Basically hold the cutter to scrap wood on the lathe so that it turns and touch up with a diamond file.
Mine are about 10 years old and I can hardly tell any wear.