Have you ever noticed that all files are not flat? Not knowing any better I just assumed that files were straight and flat. After checking several newer and vintage files it seems that almost all have some twist in the file. I measured up to 3° of twist in some files with dead flat files being the exception.

For normal hand filing the twist is not really a problem. However I sometimes do file the flat cutting edge of the cutter teeth to remove pitting or roughness so that a sharp cutting edge can be created on the cutters. In that operation I hold the far end of the file tight against then body of the saw with one hand and the other hand holds the near end of the file on the face of the cutter. In this operation a twisted file is a major issue. If a twisted file is used you end up with the cutters not being in line with the axis of the saw and that can cause the kerf to get smaller and smaller as the saw advances down through then log.

How to check to see if a file is twisted? If it is badly twisted it can be laid on a flat surface and you will be able to rock it back and forth by pushing on opposite corners. The file can be placed in a vise and a short level used to check each end, if it is twisted one end can be set at level and the other end will not be. Also as pictured below the file could be placed in a vice and straight edges be balanced on each end. Then sight along the top of the straight edges to see if they are in the same plain.

So, what I learned is that if I’m going to flat file the cutters I will have to find a flat file or come up with another method to clean up any pitting on the cutters.