I wad hoping you'd reply-- Which do you prefer and why?
Unistrut on threaded rod V ally ladder
Pro, Unistrut Bends less than cheap ladder and more than expensive ladder in the vertical direction over longer span, adjustable for width of log (this is important see below), stronger fixing to log ends
Con, Unistrut is MUCH heavier than ladder, twists more than ladder but can be held firm with strong fixing to log, more expensive than cheap ladder - less than expensive ladder
Overall the unistrut is better than the ladder provided I don't have to carry the unistrut too far.
With my ladder set up, I find that when trying to mill with the pith, one end of the ladder sits in the air, so to speak. The big heavy powerhead either sags one side, or the chain draws the ladder into the log, invariably making an un-level cut. Obviously, when the whole ladder sits on the trunk of the log, the rungs support the ladder, making a level, even cut the entire length...
Here is what I do with rails.
1) Place ladder on log and using a screwdriver mark the bar either sides of the rungs or all thread rod
2) Remove ladder and cut notches in the top of the log between the marks
3) Replace ladder and make sure that most of the ladder legs are resting on trunk.
Clamp the ends of the ladder to the log - clamping mechanism shown in post 2 above.
To stop the powerhead from slamming the mill into the ladder (a flaw with most mills!) you need a different mill design with wheels - like this.
By making the rails narrower than the log the wheels on the verticals ensure the mill hits the log before the powerhead hits the rails.
When milling the top half of the log the black wheels stop the mill from contacting with the rails.
When milling the bottom half of the log wheels are needed in a different place - like the white ones shown here. The location of the white wheels need to be adjustable to cope with different thickness slabs/boards
Details
here - make sure you read to the end of the thread.