Replies

1. 
   jharveyb | Nov 29, 2021 09:10am | #1

   I'm having a bit of a problem with the terminology of your question.
   First, let's clarify that the shoulders of the tenon will always need to be angled at 15º.
   Second, you can either have the mortise ends perpendicular to the surface of the wood, or angled at 15º. In the first case, you angle the narrow edges of the tenons 15º. In the second case, they are straight with respect to the orientation of the piece.
   So to answer your question: at low angles like 15º, there is no functional difference between the two methods, and you can pick which one is more convenient with the particular methods you use to cut the joint. At more extreme angles, you run into short grain weakness for some significant part of the tenon, which weakens the joint.
   I typically use a hollow chisel mortiser and single end tenoner to cut mine; with these, making the mortise ends perpendicular to the face of the wood would be easiest. My mortiser table doesn't tilt. If I were chopping the mortises by hand, I might angle the ends as it would be pretty easy in that process. The main advantage of having the mortise at 90º is that it is generally easier to mess with the tenon out in the open than the mortise down in a hole.

2. 
   DRBWWing | Nov 29, 2021 09:51am | #2

   I don't think it matters, I've done it both ways - tenon parallel to apron and mortise 90° to leg. I think a parallel tenon/angled mortise is easier.

   Optional here, on a larger table a stretcher would make it bomb proof.

3. 
   daverichards | Nov 29, 2021 10:03am | #3

   "he cuts the mortise and tenon at 90 degrees, despite making the piece itself angled. is there any science or reasoning to that?"

   In the video he indicates the reason he cut the mortise at 90° is so when the pieces are clamped up during gluing, they don't tend to slide around. See about 7:30 in the video.

1. 
   jharveyb | Nov 30, 2021 07:06pm | #4

   I still think there is no significant reason to do it one way or the other. In either case, if you put a clamp from the bottom of the leg to the mortised piece, the angled shoulders of the tenon will cause the piece to slide sideways until the tenon is against the end of the mortise. The only way to not have things slide is to apply clamping pressure perpendicular to the tenon shoulders (which you need to do anyway to guarantee that the shoulders fit tightly against the mortised piece.)
   I typically clamp blocks to the pieces that provide clamping points that apply pressure in the proper direction. I always do this with miters, rather than using the bogus miter clamps that clamp each board perpendicular to its length.
   I'll attach a picture of a glue-up for two boards edge glued at a blunt angle. Even tho it is not a mortise and tenon joint, the principle of aligning the clamping force perpendicular to the joint is the same.

   
4. 
   Joseph8691 | Nov 30, 2021 11:23pm | #5

   I typically use a hollow chisel mortiser and single end tenoner to cut mine; with these, making the mortise ends perpendicular to the face of the wood would be easiest. My mortiser table doesn't tilt. If I were chopping the mortises by hand, I might angle the ends as it would be pretty easy in that process.

5. 
   rob_ss | Dec 01, 2021 03:12am | #6

   As others have said - matters not, it will work fine.

   The strength of the joinery needs only meet the design needs plus whatever additional loads it might be subject to in future.

   The wider the splay, the more faults in joinery may be exposed as rotational forces will be applied to the glue joint. You'd still have to jump on it to break what you describe though.