Lap dovetails vs. tenons is an interesting subject.
Personally, I like the laps, you can make a quite elegent look if you wish it with these, or alternately by using a simple dovetail design with a steep angle, can get a rather archaic, almost medieval aesthetic.
It seems to me, lap braces and bents are usually not together. But I am used to a different tradition as well.
My like of the laps may also be culturally biased, it's common practice in the Swiss Canton of Bern where we come from.
I've seen a lot of these braces, so long as the stock is good (it does not have to be perfect) they are fine.
Make the braces 4 inches deep and the lap 2 inches, for example. a Depth of 2 inches is unlikely to twist out of the pocket.
In general, if you make the depth of the brace equal to or greater than the width of the brace, then twisting will not be a serious problem. Also, I usually see the depth of the dovetail as one half of the depth of the brace, or even a little more.
As for bearing surface, this is not as much of a concern as you might think, because the braces act in both compression AND tension. With a tenoned brace, you have the problem where they cannot resist tension, except by the strength of the pegs securing then. I've seen where a strong wind has gone under the roof of an Indiana barn and pulled the braces free, because they are not capable of resisting the resulting tension. The braces are designed to act in series, under normal circumstances the compression of one brace will cancel the tension that would be placed on a corresponding brace.
The lap dovetail works similarly, any excessive compression on one brace is counteracted by the corresponding brace's ability to act in tension. The difference though is that any single brace can be expected to act in both cases.
My opinion is that lap braces are superior in roof structures, where loading is uneven and unpredictable. You can not always expect a series of braces to be able to handle a given situation (such as the wind torn barn previously examined) and I feel much better knowing that every single brace has the ability to act in any possible scenario. But it's all a matter of opinion, BOTH systems have proven themselves to work MOST of the time, and BOTH systems have proven to be flawed PART of the time, a very SMALL part.
So in the end, I think it all comes down to what you like. I pick lap dovetails at a steep angle, because I think they look nicer. Structurally, I have more bracing than is technically necessary anyway.
Last edited by D L Bahler; 08/08/13 04:41 PM.
