Just wanted to post a recent experience which may help someone. I had always hand filed in the field. This worked for maybe 360 hrs of hardwood slabbing and cookies. Eventually I found myself pushing hard, really hard, to get through the cut. Checked rakers, thought it was the log, sharpened and resharpened- nothing seemed to help. Saw a milling video by “Flowering Elbow” on YouTube. Suggested that the hand filing would basically over time change your tooth angles and stall the cut. I purchased a $200 ish Oregon grinder, set the appropriate angles, and ground the chain (all teeth even). Didn’t touch rakers. Went to test on some 28” black cherry and the saw basically pulled itself through the cut! 2 days earlier I was having to put lots of weight into the same log. I can’t believe I waited so long to get a grinder. Basically, as I now see it, resetting the teeth to same and proper angles is a necessity and needs to be carried out periodically. Hope this helps someone