I am making a small side table (19x29x19) table that attaches the legs by thru-tenons into the top. The top is 1″ thick, legs are 1 3/4″ square with a flair toward the bottom. Typical construction I have seen uses tenons about 1 1/4″ square or round with a central wedge. I have read a lot on the design of wedged tenons, but nothing explaining this large of a tenon. All discussions assume a flared mortise and a tenon that bends under wedge pressure.
For this application, is the mortise flared in the usual manner? Can one really expect a tenon that thick to bend? Or is the mortise square cut with the wedge just snugging things up and providing a decorative touch? If so, it seems that one would want to cut a larger kerf in the tenon to allow sufficient wedge to show. Thos. Moser uses lots of these center wedged tenons that are round, and it seems hard to believe they taper cut all the round mortises. I have also seen large square wedged tenons in other “Arts and Craft” furniture.
Any help would be appreciated. Thank You;
Louis
Replies
Hi Louis,
I wanted to jump in with a quick recommendation while you wait for a reply from Gary. Here is an article we published a while back on wedged mortise-and-tenon joinery. It might answer some of your questions.
Also, in my limited experience making wedged tenons, you would be surprised what a wedge can do to a tenon when you start driving it in with a hammer. At the least, you can cut the tapered mortise at a slightly steeper angle than is typically recommended.
Matt Berger
Fine Woodworking
Matt,
Thanks for the reply. I already had a copy of that very fine article sitting in my pile of reference material. I just recently found another article that does use wedged non-tapered mortise/tenon joints in FW #113 by Jim Richey. It suggests fat 3/32 kerfs to get the desired look. Your suggestion of using a shallower taper also makes great sense.I am amazed at the info available in the FW archives - its worth every cent of my subscription cost.Thanks Again,
Louis
Louis,
It’s my feeling that wedged tenons work just fine without tapering the mortise. In fact, I have found that tenons can split under too much wedging pressure. This can certainly occur if you widen your mortise.
Because of that fact, I often drill a round hole at the bottom of the wedge slot to spread the pressure out around it. I showed this once to a student helper of mine who said oh yeah, Fracture Mechanics. She brought in a book on it the next day. There’s this whole world of structural engineering that deals just with this issue of fractures occuring because of too much stress. The quick fix is to drill a hole at the bottom of the crack.
I apply this same principle to my wedge slots, drilling a 3/16" hole at the bottom of the 3/32" wide wedge slot. My wedge is about twice as thick as my slot and never too long so it bottoms out and cracks the tenon. You’ll be amazed at how far a wedge will drive and amazed at how strong these little things are.
As for round tenons, taper reamers can be used but usually from the bottom up and not the top down on a seat. Keep your tenons tight and pound in that wedge and it’ll hold just fine.
Gary
Gary,
Thank you for taking the time to reply. You've covered the areas of my concern. I'll make a trial run to make sure I have a design that works.Louis
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