Replies

1. 
   gulfstar | Jul 07, 2022 03:58pm | #1

   Tenons and mortices can be 5 inches wide, but if this is a concern to you you could do a haunches mortice.

2. 
   jharveyb | Jul 07, 2022 04:50pm | #2

   To elaborate on Gulfstar's answer, you can make the tenons 3" wide, with haunches to within 1/4" of the apron's edges. If you center the tenon in the 6" end, that would leave 1.5" at each side, so the haunches would extend 1/25" on each side of the tenon. I typically make the haunches about 1/4" long, with the corresponding mortises a bit deeper to allow clearance. I also make the haunches' mortises slightly longer than the haunches to allow for a bit of seasonal dimension change. The haunches' job is strictly to keep the non-tenoned part of the apron straight; they are not glued at all.

   Where you locate the tenon in the end of the board depends on a variety of factors. The closer to the top of the leg it is, the less dimension change between it and the top edge of the board where it is flush with the top of the leg. However, the closer it is to the top of the leg, the more fragile the leg becomes; the more likely any stress on the leg will break the leg. For narrower aprons, I put the tenon near the bottom and put a haunch above it. In your case, I think centered would be a pretty good location.

   By the way, the shoulders on a tenoned piece add a significant amount of strength and durability to a joint. So I wouldn't try to mortise the entire 5/8" into the leg. Probably best to do a 3/8" tenon with 1/8" shoulders on both sides. Max would be 1/2"; the shoulders would be pretty narrow.

   You are correct in thinking that wide tenons are stressed. A mortise and tenon joint features cross-grain construction, with its associated problems as the tenon gets wider. Sometimes it seems that folks assume that more glue surface equals more joint strength, but there are limits imposed by wood's characteristics.

1. 
   user-1119017423 | Jul 10, 2022 12:17pm | #3

   Thanks to Gulfstar and JHarveyB for your helpful comments.
   I assume that the key in this case is to "make the haunches' mortises slightly longer than the haunches to allow for a bit of seasonal dimension change", as explained. I was also suggested the use of tween tenons, but I couldn't find a rationale for the stress-related seasonal changes, although I suspect this might reduce the weakening of the legs.

1. 
   jharveyb | Jul 10, 2022 02:09pm | #4

   I don't see any reason for twin tenons in this case. You should only glue one or you risk splitting the apron between them. One good one is strong enough. And it doesn't unnecessarily weaken the leg.

1. 
   user-1119017423 | Jul 10, 2022 02:27pm | #5

   I totally agree. In what circumstances should a twin tenon be used?

3. 
   DRBWWing | Jul 11, 2022 10:17am | #6

   You want to do haunches regardless of tenon length.

   Twin tenons are perfectly fine and maybe the way I'd go. 1/4" groove between them.