This is an exploded view of a brace tenon and its mortise. This brace is centered on the tie beam (which has been rotated so you can see into the mortise.
The brace tenon is centered on the brace.
This type of mortise and tenon joint is a little more complex to cut as the shoulders of the mortise have to match and the shoulders of the brace have to fit on either side of the tenon.
The brace is 4×6, and the tenon is 2″ thick.
If your timbers are planned, this type of joint is more straightforward to cut.
Use template with Router on Knee Brace with Centred Tenon? for 16’x20′ project so explain me about it?
You can if your timbers are planed on all four side and the dimensions are true.
With planed timbers the surface that the mortise housing is cut into is flat and 90° to the adjacent faces. The router can be set to the correct depth and it will work if you are accurate with your layout.
Trying to do it with rough sawn timbers will be a challenge as the timbers may not have faces that are truly square to one another.
The measuring point for the leg of the triangle is difficult to cut accurately in rough sawn timbers with a router and template because the timbers surfaces may not be 90° to each other.
Jim Rogers
Is the 45 degree cut inside the mortise structurally significant? When using a chain mortiser it’s pretty much impossible to cut at that angle. It’s much easier to just hollow out a square completely. When examining forces it appears to me that the extra material within the mortise is not contributing much to the overall structural integrity. I am not a structural engineer so just looking for advise/confirmation. Is it common for people to just square out the entire mortise when using a chain mortiser?
You can make it a 90. All the machine cut frames are that way. You can cut them with a Makita but they are more difficult.
Mortise does not require a 45° slope, as mentioned with the chain mortiser you just hog out all the wood in the mortise, and it will be fine.
Thank you Brice and Jim! Much appreciated. 🙂
Knee braces are typically designed for compression. When the knee brace does go into tension, the only force holding it together is the peg. If the mortise is cut with all straight sides and the tenon has a notch cut into it on the 45 degree side to accommodate the mortise, will the notch in the tenon help reduce the tension in the peg?
Braces are in both tension and compression, that is why they are in pairs. When one is in tension the other is in compression and they offset each other. This does not make the tenon nearly as important as the pocket for compression. We have had hundreds of these braces engineered and the only issues that have ever risen was if it was in a high wind zone. At that point we had to take the pockets from half inch to a deeper dimension.