The ultimate weapon in the backyard lumbermill arsenal is a bandsaw lumber mill. These are major machinery; even the cheapest one (new) will set you back several thousand dollars. (You can google on bandsaw lumber mill and get torrents of information.)
For those of us who cannot justify such an expense, there is always the Alaska Chainsaw Lumbermill. Granberg's Alaskan Mill is a neat gadget. It costs money, but is cheap at the price. It is basically a steel frame that carries the chainsaw as you rip.
The first job is to set up a frame of wood or metal, place it on the log, and even things up.
The frame is a 2x4 structure nailed up from commercial lumber. I abhor commercial lumber, but sometimes one must swallow one's scruples to progress. (Politicians do this as a way of life.) Having done this you nail or screw the frame to the wood, being very careful where you place the nails. You do not want to run the chainsaw into a nail.
Next, you set up the mill, following the rather terse directions that come with the mill. (See Granberg site, above). The mill rides on the platform you just set up. If it is straight and level, the chainsaw will be likewise. So you take a full cut, and rip off a slab.You now have a nice neat surface on the log. The chainsaw rides on that surface for the subsequent cuts. Actually, for my first cuts with this contraption I used a piece of power pole, kindly provided by Matanuska Power when they replaced a pole, and I got a few 25mm (1") boards out of it.
I am sitting on the slab I just ripped off (literally). The power pole turned out to be either cedar or redwood. It is much easier to rip cedar than it is to rip birch.
Looks easy, doesn't it? It's not. First, in ripping the big stuff, you need a big chainsaw. I used my largest, Siegfried the Stihl, with a 50cm (20") bar, all of 61cc or so. It is up to the job if you don't force it, but just. The saw roars, and it is going full ahead all the time. When you crosscut, the saw is loafing for the top and bottom parts of the cut. Not so in ripping.
The sawdust outlet on saws is designed for crosscutting, so when you have the saw on the side, it comes out right in your face, along with the exhaust. Protective gear is mandatory. The stuff is heavy. But it makes very nice boards.
The ultimate book on chainsaw lumbermaking is by Will Maloff, and it is out of print. Mr. Maloff has a website; Will Malloff-working with wood. Mr Maloff advocates a 120cc (or more) saw, along with meter-plus length bars. Another unjustifiable expense. But if I was cutting up the monster trees that he does, I'd have to do it or pass up the lumber. See his website, and look at what he's ripping up.