Sunday, October 9, 2016

The French Guitarde by Adam Miller

Adam Miller  published an article in the Timber Framing Guild's magazine last month and since it was the first French guitarde model built in the United States by an American carpenter I wanted to share it on my blog.  It's great to see an American carpenter studying L'Art du Trait and understanding it like Adam.







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-Adam Miller, October 2016

When it came time for me to get serious about my compound joinery, I decided to work through a series of exercises in the Billon Freres classic, L'Art du Trait de Charpenterie. Originally published over a century ago, Billon Freres remains in print through Editions H. Vial in France.
The guitarde is a bold statement of what l'art du trait can create. Quite in contrast to today's world of computer modeling and speed squares, every piece of information required to build the guitarde is drawn on a single sheet of paper, the epure. In the photos, you can see the elevations of each component folded down around the central plan view of the guitarde. Lines from points in plan intersect with reference lines to define the curves in the elevations. Directly transferring series of points in plan and elevation onto the work-piece yield multiply curved components and the corresponding compound (and curved compound) cuts to mate them together into the guitarde.
The other photos show the two capucines I built as preludes to the guitarde. The first is rectangular in plan with irregular hips and jack rafters. The second is similarly framed, but adds the curved tenailles, or pincer braces. All of these forms are variations on hip framing.
These models range from about 8” to 12” wide, and the group photo shows all three in a single mortise cut in a massive pine log.











Saturday, September 3, 2016

Developing Bevel Angles on the Stick-Timber

After developing the bevel angles on the hip rafters and jack rafters I realized I could develop the bevel angles on the actual purlin rafter as well. The cuts on a purlin rafter are the same as frieze blocks.

Here's a picture of developing the purlin rafter miter and bevel angle on the stick for an equal pitched roof.





Here's a drawing showing how to develop the bevel angles for the hip rafter or jack rafter on an equal pitched roof.



Drawing showing how to develop the purlin rafter miter and bevel angles for equal pitched roofs, without using any math or geometry.


Drawing showing how to develop the purlin rafter miter and bevel angles for an unequal pitched roof, without using any math and just a little bit of geometry.


Some step by step drawings showing how to draw out the purlin rafter miter and bevel angles on the stick for an equal pitched roof with a plan angle of 45°.






Here's a drawing showing how to draw out the purlin miter and bevel angles for an Octagon roof with a plan angle of 67.5°. You would have to draw this out on a piece of plywood then transfer the dimensions for the miter and bevel to the stick.







Sunday, August 28, 2016

Compound Hip Rafter Head Cuts

There are different methods for cutting compound head cuts on hip rafters, I think this method makes laying out and cutting the compound cut pretty simple.


On our current framing project we have a 45° plan angle hip rafter, 60° plan angle hip rafter and a 15° plan angle hip rafter(sloping ridge) interesting at the same location. I used plumb lines from plan view of the hip rafters to layout the compound head cuts. On an equal pitched roof, we normally measure back half the thickness of the hip rafter material , perpendicular to the hip rafter head cut slope   line , and set our saw to a 45° saw blade bevel angle to cut a 45° plan angle hip rafter head cut. On these 6x12 hip rafters the intersection of two hip rafters required a 52.5° saw blade bevel angle. None of our saws would swing over to the 52.5 saw blade bevel angle so we had to cut some of the head cuts with a hand saw.









Here's the drawing I used to layout the hip rafter head cuts. You only need a full scale drawing of the hip rafters intersecting in plan view.


Using the plumb line dimensions in plan view of the hip rafters, allowed me to easily layout the 6x12 hip rafter head cut accurately without knowing or caring about the hip rafter bevel angle on the tops of the hip rafters.  Knowing the intersecting angles of the hip rafters in plan view did allow us to set our saws to the saw blade bevel angle. However, like most saws the saw blade bevel angle settings on the saw are never accurate. We made a couple of test cuts to determine the correct bevel angle on our saws.  






We would have probably had to finish off the head cuts with a hand saw, even if we had a Mafell MKS185Ec carpenter's portable circular saw.
The 18" Mafell beam saw blade bevel swings over to 60°, but I'm not sure about the depth of the cut at 52.5°. At a cost of $5,410.00 , that would have put the cost of the hip rafter head cuts at $2705.00 per rafter.














Saturday, July 30, 2016

Simpson Strong Tie HRC44 Hanger Installation


This is my version of Simpson Strong Tie HRC44 Hanger Installation. Simpson website says to double bevel-cut hip rafter members to achieve full bearing capacity with HRC hangers. The HRC22 and HRC1.81 hangers for single hip rafters work correctly with a double bevel-cut on the hip rafters, so the hip rafters can intersect at the correct roof plane location point. However, the HRC44 hangers for hip rafters were not designed for double bevel-cut hip rafters. Simpson wants you to square cut the ends of the hip rafters to work "correctly" with their HRC44 hangers.  I find this very unacceptable when your installing hip rafters. 


In these pictures of the hip rafters with the HRC22 hangers you can that worked correctly with a double bevel cut on each hip rafter. 







I installed  HRC44 hangers about 5 years ago and don't remember how I got the HRC44 hanger to work with double bevel-cut 4x10 hip rafters. I must have beat the hanger into place or I cut the double bevel cuts differently or square. 







This time I cut some 4x6 blocks with a double bevel cut with zero pitch to determine what I needed to do to correct the installation of the hip rafters into the HRC44 hanger. 







With a 1/2" gap at the back of the HRC44 hanger with double bevel cut hip rafters I decided that notching the ridge beam an 1/2" would allow me to install the hip rafters into the HRC44 hangers with double bevel cuts, so I had could achieve full bearing capacity with HRC hangers. Where  the hip rafters intersect at the ridge, at the correct roof plane location point, I installed 2 -- 6" SDS screws from the hip rafter to the ridge to keep the hip rafter from rolling/ bending away from the ridge.