Attachning wide aprons to table legs
This is basically a question about frame joinery and seasonal wood movement, specifically between table legs and 9″ wide aprons.
I am ready to make a small two-drawer end table. The design calls for 9″ wide x 18″ long solid wood (mahogany) aprons on the sides (9 x 14″ on the back), joined to the legs with 6″ wide tenons.
Obviously it would be easier to make aprons with the grain running the long (18″) direction. I would do this without question if the aprons were not so wide. To get 18″ of vertical grain, I can glue up panels and then cut them to 9″ wide if necessary.
I have considered veneered plywood but I have some 5/8″ mahogany that I would prefer to use. Also, I want to learn the correct way to solve this problem with solid wood, if there is one.
Do you think it is necessary for the grain in these wide aprons to be parallel to the grain in the legs?
Hi, I just ran across your question... don't know if you've gotten any answers yet.
If not I'd recommend looking at construction techniques for things that have a similar situation as your wide apron. The first thing that comes to my mind is where the headboard on certain styles of beds join to the post with a wide - or two wide - tenons.
The other immediate thought is a breadboard end on a tabletop. The breadboard end is basically a series of tenons cut on the end of a wide board that fit into mortises in a board with grain running perpendicular to the top - same basic situation.
The solution is to glue only a portion (on the headboard the top tenon..., on the breadboard end the center tenon) so that the remainder of the tenon or tenons can "float" - move with the seasons. Usually the tenons are pegged, also, which means that the peg going through the unglued section must be allowed to move, also. This is done by pre-drilling the hole for the peg with the assembly together (no glue yet) removing the tenon and widening the hole (in the tenon only) lengthwise. Also, the mortise must be wider than the tenon so that the tenon can expand (how much depends on the season... relative humidity... MC of your wood etc.)....
I'd recommend looking up articles by Christian Becksvoort on the subject. He has covered your exact situation - I just can't remember the article/FWW issue etc. Becksvoort is an expert on the subject. The articles are illustrated which helps, also.
Another interesting option is the drawbore method of pegging tenons which does not require glue - check out the Woodworking Magazine blog posted by Christopher Schwarz.
I would definitely run the grain of the apron perp. to (not parallel with) the leg. The strength of the apron would be compromised otherwise, and visually it would look funky. Edge gluing boards to get nine inches is the way to go.
Thank you. I usually try to start on a problem by thinking of analogies, as you did, but I had not thought of either of your similar examples. The headboard to bed leg joint seems an excellent analogy.
I did come to a similar conclusion, however. I agree completely that vertical grain would compromise the strength of the aprons. I should have recognized that myself.
The literature seems to approve of gluing 4" M/T aprons to legs. I decided to use sliding dovetails and to glue the top 2-4", leaving the bottom to slide with expansion and contraction. Also, the tail (mortise) will be 1/2" longer than the pin (tenon) and concealed by the shoulder. A prototype made out of pine seemed to make a nice stiff joint. I routed out the tails yesterday and will cut the pins today. They of course will be the harder part of the joint, if they are to slide yet be tight. I'm wondering whether I can shave a bit off the pins to taper them with hand tools. I would like to know your opinion of this solution.
I had actually researched this question. Frid, usually the gold standard, just recommends double or forked tenons, as do others, but that would not address the problem of wood movement unless you didn't glue the lower tenon, which he does not mention. The Taunton CIG to Woodworking does not seem to address the problem, at least not in the index. And can you imagine how many totally irrlelvant hits I got when I searched FWW.com for table + apron + wide? I don't mean to be defensive -- just to point out that Ask the Experts can be quite important even for people who try to answer their own questions.
Thanks for your advice, and I look forward to any comments you (and any other reader) may have.
If you go to the FWW Online home page and do a search for 'Christian Becksvoort' you'll get a ton of hits, but two in particular address the issues of wood movement, gluing and pegging tenons and grain orientation.
1. Keeping Tabletops Flat - C. Becksvoort (within 1st 25 hits)
2. Understanding Wood Movement - C. Becksvoort (somewhere between 25-50)
The sliding dovetail thing is a bit tricky, and I can't explain it very well, but Garrett Hack does in the last issue of FWW - Building a Cherry Sideboard(?) He uses sliding dovetails in part of the carcass construction. Basically the easiest way is to tweak the female part of the joint (for lack of a better term.) You want that part of the joint to taper a tiny bit - wider at the front - so the tail doesn't bind as it is slid in. If this is not a possibility i'd try to shave the tail w/ the bit on the router table somehow. I don't own any hand tools that would do a good job of shaving a tail that way - maybe an old school dovetal plane...? I don't use that joint much, but I never approached in any way other than to either make it fit (force - not always the answer) or by tapering the slot.
Actually, the article on wood movement is why I gave this issue priority. That, and the fact that the original table (of which this is will be a copy) had split sometime in the past because of wood movement. I will check out the other article. Thanks.
I had a good day in the shop. I cut the pins, perhaps a few thousandths too fat and trimmed them with a dovetail plane, taking more off the bottom side than the top, so roughly tapering them along their length. Five of the 6 fit very well, i.e., I can slide the joint together with moderate resistance. They are tight, no wobble, dry-assembled. The sixth pin is narrow by about 3/32. I hand- surfaced the aprons and one end of that board was a bit thinner than the others. I know that this is always a problem when you cut by subtraction but I was too pre-occupied by all the other setup issues. It is always possible to make a beginner's mistake!
I am happy with the result and I believe that these joints will stand up for many years. Cutting the pins was slow, fussy work because I was figuring it out as I went along, but I think the second time would go faster, about the same as straight M/T work, maybe easier than making forked tenons match the position of paired mortises. Plus, these joints have lateral strength both forward & back and side-to-side. I'd do it again if I ever confronted this problem again (i.e., if I had to make such wide aprons).
Now -- about the dovetail plane. I inherited it from my father, and he, probably, from his older brother. It is obviously a hand made wooden plane, just a block of dense wood with a blade and wedge in it. It still has faint saw marks on the sides. For a long time, I didn't know what it was or have any use for it, but luckily I kept it. When I got interested in hand planes I figured out what it probably was and sharpened it. It has been sitting in a drawer ever since. It happens to have a 1:6 angle that matches my 1/2" DT router bit. There is a moral to this story, somewhere.
I appreciate your advice, and thought that I should let you know how this part of the project came out. Cheers.
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