In this picture you can see that the rafters do not extend past the wall. Rafter tails will be added to extend the rafters to provide for an eave. Doing it this way will make room for insulation without having the appearance of a 1 foot thick roof from the outside.
So the rafter tails need to be natural log for the lower half and milled to 3 1/2 x 7 1/4 on the upper half. I built a 6' long box that will hold the log. I attached temporary 2x4 blocks to each log end. The blocks and the box have holes drilled in them so that bolts can be inserted, allowing the log to spin within the box.
The end block is exactly the same dimension as the 3 1/2 x 7 1/4 section I need to cut. For each cut, the saw blade is brought down to just touch the block. The log is rotated to position for the first cut and a screw is driven to hold it from rotating. Cut 1 is made.
Before rotating for the next cut, the side of the log is scored with the chainsaw for the plumb cut that aligns with the exterior wall face. A slot in the box positions this cut in the same place on each rafter tail that is made.
Rotate 90 degrees and set the saw blade height for the next cut...
Finish the plumb cut with a chainsaw..
And so on until all 4 cuts are made.
Here are some rafter tails installed, along with some blocking.
