The chainsaw mill, or Alaskan mill as it is sometimes called, is pretty simple. You start with a straight reference edge atop the log you want to plank up (a ladder makes a good straight edge). The ‘CS mill”, which is the chainsaw mill, which is the jig attachment you build, holds the chainsaw’s guide bar (GB) below and in alignment with this straight reference edge. That way you can cut a nice flat surface parallel to the straight edge. Once you have a flat cut into the log you can do the same thing but using the straight edge you just cut, rather than the ladder.
Adjustability. The idea for this mill was to have it very adjustable. Obviously it will be necessary to adjust the distance between the CS guide bar and the guide rails of the CS Mill, as this determines the thickness of the slabs (or in some cases beams, or posts, or whatever) you will cut. I also wanted to be able to easily adjust the outboard end of the mill to accommodate different sized guide bars. This is a kinda future-proofing – especially if your current saw isn’t running the biggest guide bar it could, you are likely to want to run a bigger one in the future.