Timber Framers Guild Forums General General Forum Questions Lapped Dovetail vs Tenon&Mortise Knee Braces

well I have been to Canada at the Pat Wolfe Log Building School, during that period, my interest in Timber Framing started and i bought few books, and amongs them the one from steev chappell.
I have not been studying carpentery in France. I was interested in building a "ferme sur blochet" for the bent number 2 but I didn't feel comfortable getting into it alone, so I sticked to those books.
And here in Norway, they kind of lost their tradition in building with wood, i mean not stick frames.

I would like to go to Canada after that house and work as a log builder for a while, so it's a good experience to take with, building a timber frame now, all by my own, from scratch. I would like to learn other technics later too, not only in timber framing but in log building too (the norwegian ones for example).

Concerning the girts, i don't think i'll include them, but thanks for the tip. I will just make my frame tight and will give special attention to the outside framing in order to make it react as well if necessary.

OK as promised, here are some photos of half lap dovetail joints and their variations. The idea here is to show different approaches to the refined entry concept, which is an attempt to solve the problem of shrinkage opening up the dovetail and weakening the joint.

The concept is that, in general, a sharper angle will gap less, that is the closer the angle is to perpendicular to the grain, the less it will open as a result of shrinkage. But the flaw here is that the sharper the angle, the weaker the connection can be. The the solution is a double angle, or refined entry. Hope that makes sense. Here's pictures:

Some of these are refined, some are not. This gives you an idea.
You may have to right click, and click 'view image' or 'open image in new tab' or whatever version of this function your browser uses.

braces like those in the 4th picture are most prone to opening up, as this one appears to have done. Those executed as in the last picture are the most secure due to the complexity of the angle. The shape of the lap is not only attractive, but its gentle angles help preserve the integrity of the post.

The last image on the first page is an example of a steep angle without a refined entry. this has the potential of causing a split or excess twisting in the brace.

The fifth image is also an example of particularly well executed lap joints.

Hei, thanks for the pics DL Bahler.

look, I draw this as solution fitting the hole allreday made on the timber which is 8cm deep and 17,9cm wide from the 75cm mark. What can you tell me about it? good, not good? angles, measures etc..?



If anyone is interested in the discussion going on and have some good inputs, please just share as well!

I'm not sure I understand the previous message you posted:

"The concept is that, in general, a sharper angle will gap less, that is the closer the angle is to perpendicular to the grain, the less it will open as a result of shrinkage. But the flaw here is that the sharper the angle, the weaker the connection can be. The solution is a double angle, or refined entry. Hope that makes sense."

Which angle are you talking about? (sharper angle)
sorry I don't always have the right words for technical issues.. thinking about "refined entry"..


I'm looking for answers, since I have to precut holes before end of this week.

Have a great day! Neil

here you can see my tie beams. the one on the left in the center one (bent 2), everyhting is allright with it, it's going to get tenon and mortise knee braces. but the two next beams on the right are the tie beams for bent 1 and 3 and they are going to be lapped dovetail knee braced. you can observe the mortiser cut (4 of them) on the beam with the brush. that's where I need to fit my braces as mentionned in the post before..

The tenons should be longer, as talked about earlier, an advantage to lapped dovetailed brace work is it may help in tension as well as compression. with short tenons I don't see that being a bonus.

The angle in question is the angle of the dovetail on the short side of the brace relative to the vertical line of the post

I'll need to make some drawings, the concept of the refined dovetail is somewhat complicated.

I've seen dovetails of about the size illustrated, they work. Note that holding strength here is different than a tenon. A tenon relies on relish -wood past the peg- to hold, the holding wood on the dovetail (which is on the post) is secured firmly to the post and is much stronger than relish.

sorry if this isn't entirely clear

That is a reasonable point on the length of the tenon on lapped braces,DL. Of notice, in the majority of the pictures posted above the tenons are much longer then the sketchup picture.

yes that's true, and personally I prefer them to be much longer. Just thought I'd point out, they do appear to work when cut shorter as well.