Drill bit web thinning.

[Frank S]

I find that the fixed attitude of the grinder angle does not match well to the factory grind of many chains.
Like preciously stated by suther51 good for pulling the last little bit of use out of an old chain.
I won't use mine on a fresh chain that has had less than 2 dozen hand filings done to it. My grinder spins at 6500 RPM hence is why I use only the 10,00 RPM or better disks