Today I was talking to the guy who took the chainsaw course I just completed and we were talking about chisel chain. He told me that the chain we had used during the course was 3/8" square chisel chain. During the course we had sharpened the chains quite a lot of times with no problem and it cut VERY fast after each sharpen. Then just yesterday I was looking at saw chains on a saw shop's (in the PNW) web site and it said that square chisel chain is very hard (if not impossible) to sharpen with a file and that if you are going to run it you should buy a grinder. The guy that took my course very much disagrees with that and says it is a sales pitch. I am new to sharpening saws and like I said I had no trouble sharpening the chain with a round file and it cut great. What is your opinion? Is it a sales pitch or has the guy somehow made a mistake on the type of chain we were using? Thanks