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.