Curious about how long a round file should last. My first file was a stihl round file without guide and I initially was sharpening freehand. It lasted a good bit but I replaced it as it felt slick and lost its bite. I now use a guide and figured if I rotate the fileI can evenly wear on it. I am assuming these are not nicholson quality files.....cheapo stihl files. Under normal conditions how long should a round file last me.....how many sharpenings before I toss it out? Do they need to be cleaned at all for metal shavings? Thanks!!