For the ones that need a new chain after four sharpening(s), you need some guidance on how to use the grinder!For the ones who grind your chains you will need a new chain after four sharpening if that.
Several years back I posted a thread on some rough numbers on 'chainsaw math', and still use those today in training. Although it will vary with the saw, a cutter on a 16" bar travels around the bar about 20 times per second (!!!). So if the chain only touches the dirt for 'about half-a-second' , that means . . . .I pointed at them and said that’s why your chain is dull. He said, oh,that little bit doesn’t hurt. YES IT DOES.
https://www.arboristsite.com/community/threads/chain-saw-math.107300/
Philbert