After isolating the location of the main bearing post, a 24″ diameter, 18′ tall Douglas Fir, we could lay out the location of the “D” logs that will hold up the bastard valleys around the stairway opening.
As you can see from the video, we used four string lines to find the center of the main bearing post; Old Glory is what we call him. Because the layout of the timber frame is based off of a mathematical grid, and because Old Glory holds up 9 different timbers, this allowed us to pull both main axis ridge lines as well as the two bastard valley center lines; where they all intersect is the center of Old Glory.
We placed a large wood pad where Old Glory goes and then used a transit to both level it and to calculate how long to cut Old Glory for installation. We placed the pad below the final post bottom location so that, once the entire frame was together, we could use a transit to mark the actual cutting length of OG.
The interior “D” log posts, so called because they have a flat face milled on one side of them, are attached to the floor system with traditional mortice and tenon joinery. As you can see in the video, the flat faces of the posts carry the plane of the stairway opening up to the ceiling which ensures that no part of the posts intrude into the stairway.
To appreciate the complexity of the layout, keep in mind that the “D” posts must be cut so that they place the top of the bastard valley at the correct elevation along it’s length. While we had theo lines placed on the posts during the bent layout in the shop, we still used a transit to ensure that the floor was at the correct elevation and that we could trust the theo lines from before. Of course, at this point, we won’t know if we did our math correctly until we actually install the bastard valleys in a few days. And that is why we say that the layout guy is at the sharp end of the spear; if the pencil line is wrong, then all the expert cutting in the world won’t save you.