Hi Milton:
Turning round logs into "rough hewn" square timbers means just that, remember that the product of the hewing process is in a majority of cases a timber with a very uneven and irregular surface more so if done by an inexperienced person. I have seen frames one in particular which was a church frame, the vertical timbers of which there were many that appeared to have been squared by very inexperienced tradesmen. In this case the principal timbers were nicely done, with the interveening timbers very roughly finished.
What I am getting at is your preoccupation of not being able to see the bottom line. There is no need for a line on the bottom, the only line needed is on the top surface. During the hewing process if the log is set up properly, and not moved, the finished side should be vertical, and as you gain experience the finished surface will be unusually straight top and bottom. I usually aimed to hew out alittle on the bottom, especially on the first side, the reason being that during the framing process when you are utilizing your product of hewing, the timber would end up slightly oversized this being better than undersized, where you could run into problems of strength, andshouldering of mortises. Personally i never noticed much warping of timbers during the hewing process, and I have worked on timbers up to 50' in length. What usually happens is as you work on the final side, the long timbers will get slightly flimsy, and it may be necessary to crowd the centre one way or another to keep the size right at the centre point. You mention the tension noticed during the sawing process, I have seen that also, but remember that the saw logs being used could have alot of wind stress inside, while the timbers that i usually selected for hewing were special picked for straightness, and size, as they probably were years ago. You also were wondering about the axe, and how I kept from knicking it during the hewing process on the ground, well for starters I always kept my axe really sharp, this meant that i did not have to strike hard, this in turn meant that I had good control as I struck downward, and could stop the downward travel of the axe usually before it broke through the bottom of the cut. Always just for the safety of the cutting edge I would work in an area with a depth of chips from many days of work. This again was a natural thing to do with one area being used usually to do these sort of jobs. In the case where you are starting in a new area I used a small 1" pine board under where I was working, until I had a sufficient build up of chips to use. In all my years of hewing, I chipped the edge of my axe once, and that was due to a hemlock knot, which are notorious for knicking axe edges especially those that are very keen, and slim tapered on the cutting edge. I hope this helps you get some idea of how I hew, the subject has somewhat of a mystery to it, it all boils down to having some idea of the technique used, and then with practice gaining confidence in your ability, familiarity with your axes, and their handles, and after a while it will surprise you the quality of timbers that you can produce, which in turn will have your marks on their surfaces.
the Northern Hewer