Timber Framers Guild Forums General General Forum Questions set back mortises

Hi all, I have seen this practice in a few shops now and was wondering how many are designing and cutting like this. Basically instead of mortising from the face of the intersecting timber the mortise is then inset X from the face so that four shoulders are created. I guess shops do this reduce visible sloppy mortises but I think it only adds to the problem ("just cut the tenon back some more" or lay-out doesnt need to be perfect). The braces are cut the same way (setback mortises for lack of a better term) only adding to design time for stick drawings, layout time, cutting time, and alleviating the consequences for bad mortising and cutting. Only on pieces with out housings in mill rule. Does anyone think that this adds up to too much wasted time (a lot more tooling, I'd would say twice as much on the stick below)?



*not to scale

No, three times as much

1. Layout
a. shoulder to shoulder
b. tenon lengths
c. tenon placement (top and bottom)
* d. lay-out "setback"

2. Cutting
a. end of tenon cut (big saw)
b. layout tenon (endgrain)
* c. layout setback (endgrain)
* d. Drop cut setback ((this would be tricky on one side, unless you want to flip the timber, Argh! not anymore than I have to),kerfing too much time)).
e. Drop cut tenon cheeks
* f. cut little shoulders
g. cut real shoulders

Basically disregarding lay-out you would have to make 8 extra saw passes (two ends). one being very trick if you do not want to kerf. One more saw depth set. This is just the quick stick (not the brace)

I use this if the tenon/mortise are taking away too much wood, as in the rafter tenon below

I don't see it taking three times as long, but quite surely more cutting. I am looking for short cuts, ways to lessen the time. Surely not on braces and or to hide a mortice after a few years of drying.

I do a similar cut to the tenon on a english tying post, the one going into the bottom of the tie beam. The post is flared or fan tailed and is 13"x9" at the top. The plate uses up 6" and the tie tenon is 6" leaving 1" on the shoulder as you have shown. I do this because in the past I have been left with a 11-1/4" post top and had to make adjustments I didn't like. So now I saw them a bit deeper and have plenty of wood for my tenons. Also this is the case when the post has a live edge on the inner face, plenty of wood then. Tim

And as Mark shows also, even more so if the rafter is pushed out to the slope. If it is my choice I cut them like Marks drawings. You can see the tenon on the post I referenced. Tim

We do it often in high-spec jobs where shrinkage will create a peeking mortise.

It is called boxing the tenon.

(I miss the edit)

We do this on post top tenons when square ruling. If the post is 1/4" wider than called for, we trim the tenon back 1/4" to the correct measurement. Secondarily, it hides the mortise when the post shrinks (as Gabel mentioned). We don't do it on girts, which are usually housed - we'll cut back the entire end, not just the tenon, and use a gradual reduction, not a square cut. CB.

Hi,

Another reason for cutting back on the edge of a tenon is to remove sap wood and hence to frame a joint using only heart wood.

Regards

Ken Hume

I don't see why it takes much longer to do this. You have to cut the tenon full size, then sizing it down afterwards is pretty quick. This is a good job for the handsaw.