Scarf joint offset or centered?

[Dana Stanley]

So I see plans, like the one featured this month in the Timber framing HQ newsletter, with the scarf joint centered over the supporting post. Is this common? I was taught that it should be off set, or that traditionally it was offset. I was told that it is stronger that way. This is what I was told at a timber framing class at Shaker Village, in Mass.

[Stephen1]

I also though that. I will follow along 

[Don P]

http://www.woodworkinghistory.com/hewett_scarfs_in_evolutionary_sequence_1969.pdf

[D L Bahler]

I had an engineer tell me one time, the reason often given for offsetting it seems logical in theory, but in practice it doesn't actually make a difference. I can't remember the whole explanation, but if I recall correctly it was something along the lines of the supposed advantage being well within the design limitations of the joint.

In my observations in Central Europe, the scarf is ALWAYS on the post. Some of these have been in this arrangement since the late Middle Ages, so I'd say it works.

Now if you want to get detailed, I think it depends on what specifically your joint and its beam is expected to do. Consider what sort of loads the beam is under, and that might lead to where you choose to put your scarf. Central European carpenters like to either use the tenon on the post to hold the scarf together, or else they place it atop a pillow block to completely eliminate the issue of a weakened beam. (which is my own personal preference, because I think it adds a certain elegance to the frame)

I suspect the reason a lot of anglo-style frames offset the joint is purely a function of the joinery. The way these frames work and the sort of scarfs they use, you're just adding an unnecessary complexity by sticking a tenon through it. It's just easier to slide the thing over. German-style frames use a completely different class of joints, and this is sort of a non-issue.