This video is a compilation showing the fabrication and initial assembly of the bastard crotch system. Having already cut both bastard valleys into their respective bent systems, we now needed to cut in the purlins and the jack rafters. Sice the bastard valleys are tapered octagons, it was impossible to cut these according to math (square ruling) and so scribing was our solution.
To scribe correctly, all of the components must be placed into space exactly where their final configuration is and then we use scribes (basically large compasses with leveling bubbles) to transfer marks from one piece to another and then we cut to those lines.
Placing the bastard valleys in space was not an easy endeavor and we discussed a few options before we settled on what we ended up doing. Using the computer, we were able to determine the proper elevation for tha bastard valley at the center line of each bearing point. Using this information, we were able to construct a cribbing system of walls that would hold the valleys at the proper position, both in elevation and in plan. It took a couple of days to fine tune and perfect the placement, but, one we had it perfect, we were ready to place and cut in the purlins.
As the valleys taper towards the peak, we thought it would be a nice touch to make each higher purlin smaller in size, so everything reduces in size as it gets higher and makes for a space that seems higher and more soaring than it actually is. Perfect, really, as high soaring ceiling are tremendously inefficient and we really quite dislike them.