Hi WC,
If the bolt [log section] is longer than my saw's bar I have two options. (1)- I can set my saw from each end of the bolt as illustrated, or (2) - I can stay at one end of the log and reset my saw from the top such that it's nose-down with the chain cutting "up" through the rings and the nose is clear of the log. Which option I choose depends upon the wood I'm cutting. If I'm working in a piece with lots of compression wood like cherry, apple or pear and the keft wants to close, I could opt for the top-set to keep the nose clear of the kerf and avoid potential kickback as much as possible. Either way, however, if my bar is shorter than the bolt, I'm going to have that nose in the kerf at some point in the cut. My big saw has a 28" bar so you have to remember that the longer the bar the more force get's imparted to a kickback at the nose. I therefore prefer cutting from both ends because I can get a firmer grip with the dawg teeth set in the end-grain, and that increased grip will help me control any kickback if it occurs. When I can't avoid putting the nose in the kerf, I will always use some wood wedges in the top of the kerf to prevent the thing from closing up on me.
This situation only comes up where I want to maintain a maximum diameter for a bowl. In that situation I'll have cut the bolt's length to be several inches longer than the trunk is wide. With a 28" bar on my big saw, I'm not too likely to exceed its capacity since I don't do many bowls bigger than 28" regardless of how big the tree is. 😀
m
PS I will keep my bar angled as long as possible, but at some point I will have to go "horizontal" to finish the cut. This is ok because at that point I've got a "A" shape left in the middle of the cut. When I flatten out my bar, I'm still getting shorter ribbons. I can also roll the bolt to put the kerf down, insert the bar and finish the cut with an up-stroke using the kickback force to my advantage to power up through the remaining wood on an angle. This cut is not to be done without a lot of caution, however, because the forces involved can get away from the operater very quickly.
M