"Traité Théorique et Pratique de Charpente"

Tim Moore's blog on Stereotomy.
The art of representing objects in section, elevation and plan in order to cut them out. - Louis Mazerolle


Tim has some excellent graphic image drawings of  devers de pas. The DP line or the angle of projection line and he has done a great job of explaining how to develop the devers de pas.


http://stereotomy-blog.blogspot.com/2011_09_01_archive.html

Geometry is a language without words.However, without being able to read French it's hard to tell if Louis Mazerolle explains how to develop the foot print of the skewed rafter at point G in the drawing on page 52.  If all of the rafters are the same width, then you need to develop the real roof surface at the skewed rafter side of the Trapezoidal Ground Plan. The width of the skewed rafter on the ground plane is developed from the width of the rafter on the real roof surface and then the lines parallel to the DP line can be drawn in on the ground plan to represent the foot print of the skewed rafter.

the Carpentry Way: X Marks the Spot

the Carpentry Way: X Marks the Spot

X Marks the Spot

This drawing was developed from Chris Halls series X marks the spot. The hip rafter foot print was developed from the typical dihedral angle geometry.

The dihedral angle, the angle between the two planes, is developed by drawing a line from the eave line that is perpendicular to the hip rafter run leg. The next line, altitude line, is drawn perpendicular to the hip rafter leg. Then swing an arc the length of the altitude line until it meets the hip rafter run leg. Then draw another line that connects with the eave line.

This drawing shows the dihedral angle drawn on the ground plan.

This drawing shows the dihedral angle drawn in 3D.