Tréteaux Fold Down Roof Surface

We're getting closer to defining the claw lines on the Tréteaux  Fold Down Roof Surface correctly. Once the claw lines on the fold down roof surface are drawn correctly you can place the lines for the timber in plan view at any skewed angle from the eave line and still develop the timber angle cuts on the the fold down roof surface.

tréteau à devers

First, here's an example of a purlin rafter on the DP side of the hip rafter rotated into the roof surface and a jack rafter on the rotated side of the hip rafter.

Here's a drawing using the same folding roof surfaces with the purlin rafters skewed from the plate line.


Here's the drawing of how the claw lines on the folding roof surface are developed from the seat lines in plan view and the seat lines on the folding roof surface. There should always be 4 lines that define the claw-miter-bevel angles of the rafters on the roof surface. These four lines represent the center line of the hip rafter, the edge of the hip rafter, the bottom of the hip rafter plane that intersects with the roof surface and the bottom of the jack rafter where it intersects the bottom of the hip rafter.


These pictures are from Louis Mazerolle's book, Traite Theorique Et Pratique De Charpente, planche 29. Now that I can develop the folding roof surface with the claw lines this Tréteaux-- Trestle -- Sawhorse doesn't look all that hard anymore. This Sawhorse has two legs rotated into the roof surface, that Louis Mazerolle refers to as Liens Mansards, and two legs of the Sawhorse that are Plumb.






Here's my first drawing of  the Tréteaux Planche 29 with the two legs rotated into the roof surface and the two legs, hip rafters, that are plumb to the ground plane.


Here's an updated version of my drawing. Using the Tréteaux Angles Check I can see that the green footprint prism was not drawn correctly.







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