The Forestry Forum

Got a set of plans that show the scarf joint on  the ridge beam and plates directly on the post instead of the knee brace. I find that this is not the way I learned to do it. Which is it.

The optimal placement for a scarf is as you learned, offset from the post slightly. The reason is that this position is actually the happiest medium of all forces acting on the beam. Shear forces are highest next to a post, but deflection is lowest. Roughly vice versa for mid span between posts. Somewhere around 1/4 of the span is there place where both stresses are about balanced.

Proper scarf blade orientation is important as well. The lower blade of the scarf should be on the beam attached to the nearest post. I hope that makes sense!

Quote from: S.Hyland on April 23, 2016, 02:59:59 PM
The optimal placement for a scarf is as you learned, offset from the post slightly. The reason is that this position is actually the happiest medium of all forces acting on the beam. Shear forces are highest next to a post, but deflection is lowest. Roughly vice versa for mid span between posts. Somewhere around 1/4 of the span is there place where both stresses are about balanced.

Proper scarf blade orientation is important as well. The lower blade of the scarf should be on the beam attached to the nearest post. I hope that makes sense!

Yes it does thanks. And the plate and ridge beam scarf should use wedges?

There are good scarfs that do use or do not use wedges. It all depends on the geometry of a given scarf joint. But yes, one of my favorite go to scarfs is the stop splayed, undersquinted, and tabled with opposing wedges. It's pretty simple to cut, yet pleasingly refined in appearance and effective structurally. You can find it (and a lot of other great scarfs) pictured in Jack Sobon's "Historic American Timber Joinery" chapter 6. If you do a search I think you can find images easily...