I am in the assembly phases of my coffee table now. I have been trying to decide whether the legs should be glued to their respective aprons, or if this will inhibit cross-grain movement. The legs have a mortise cut in the center while the aprons have a tenon that fits into the appropriate mortise. I have uploaded a quick sketch of my design.
1) In your opinion, would gluing this MT joint create problems with movement across the grain of the apron? FYI: The aprons are approx 4″ wide at the point they join the legs.
2) Would it be wiser to avoid glue and instead utilize dowels to pin the tenon?
3) If I use dowels, and assuming 2 dowels per joint, should I make one of the 2 holes in the tenon vertically wider to allow for expansion?
Any feedback would be most appreciated!
Replies
The glued mortise and tenon joint is the time honored construction used for centuries. Pegging this joint is langinappe. The mortise and tenon joint will be far stronger in this application than dowels--dramatically so. Don't get hung up on the cross grain concept here--all M&T joints are cross grain.
You speak the truth and I am not trying to dispute that. I was concerned however, because most MT joints are under 2" whereas my joint will be nearly 4". If movement will occur, I will like to allow for it now before it destroys the piece."100 Years" -- scribbled on the wall by a woodworker to remind him to do his best and as a warranty on his work -- "If anything I make fails in the first hundred years, bring it back, and I'll take care of it. After that, there will be a small charge. (Original purchaser only)"
Edited 11/3/2005 11:19 am by zombeerose
Using the slot instead of the fully enclosed mortise does cause me concerns since it has to reduce the strength of the joint. I'd still not worry too much with the wood movement aspect of the joint, it's the strength of the leg that has been compromised.
If I wanted to reduce the chance of the racking that could compromise the leg joint I might borrow a trick from John Townsend. His tables always had cross stretchers dovetailed into the rails top and bottom. Made them "bullet proof" even though he sometimes used tenons as small as 1/8".
I should have described the structure a bit more thoroughly. For one, I have a "tic-tac-toe" framework of 3/4" by 1 1/2" maple that connects all 4 aprons together w/ 1/4" DTs at each end of the tic-tac-toe (8 in all). Secondly, each leg is composed of two 3/4" thick pieces that use a locking miter to join them.Do you think this will help to minimize the racking?I can certainly visualize now why I should not have cut the mortises all the way thru the tops of the legs. However, what is done is done. I don't have time to redo the legs at this point.
"100 Years" -- scribbled on the wall by a woodworker to remind him to do his best and as a warranty on his work -- "If anything I make fails in the first hundred years, bring it back, and I'll take care of it. After that, there will be a small charge. (Original purchaser only)"
Zombeerose,
If your apron is 4" is it correct to assume that the tenon is 3" wide. The reason this is important is because some will provide for movement with a 4" tenon but not a 3" tenon. At any rate it may affect the answers you receive..
Then please let me clarify. The mortise extends all the way thru the tops of the legs. With that in mind, I was not sure if "mortise" still truly applies or if another term fits better. Secondly, the tenon portion is nearly 4" although it will not "completely" fill in the mortise on the legs once the top is attached. Approx. an 1/8" gap will intentionally remain.I hope that helps..."100 Years" -- scribbled on the wall by a woodworker to remind him to do his best and as a warranty on his work -- "If anything I make fails in the first hundred years, bring it back, and I'll take care of it. After that, there will be a small charge. (Original purchaser only)"
FWIW, I would not have the mortise go all the way to the top of the leg as drawn. If you want that effect, make the M/Ts deeper and haunch them. Otherwise, you'll lose a lot of the joint's resistance to racking forces and will need to rely on glue alone for this purpose rather than the physical strength of the joint itself. Take a look at the most recent FWW -- it has a good article on M/Ts and how to offset and miter them for the greatest strength. I've never had any problems with wood movement in 4" M/T joints. I often pin for esthetics, but with modern glues, I don't believe that pins really add much strength to a joint.
Mike Hennessy
Zombeerose,
With the apron and tenon being the same width and a through mortice going to the top of the leg, it would seem to be a bridal joint more than a mortice. Normally (what ever that means)you put a 1/2" shoulder on your tenon, top and bottom, thereby the mortice is closed at the top of the leg. Anyhow, the best advice I've seen here is figure a 1/4" expansion for evey foot of width..your talking about 1/12" expansion potential...not a lot.
zombeerose. You've illustrated what I call the 'near bridle'. There's little at the top of the leg- the end of the mortise- where if racking occurs to prevent a plug of wood popping out. Up to about 100- 120 mm (4" to 4-1/2") you will be able to glue the full width of the tenon in the mortice.
Below is a typical tenon suited for rails to leg junctions in table type structures, and others like them. The ends of each tenon are mitred at the corner of the mortise where they meet to allow maximum long grain to long grain glue strngth. Not all tenons penetrate the leg deep enough to meet at the end of the mortice.
The sketch attached also partially illustrates the rule of thirds which I haven't time to explain right now as I have to get to work. Perhaps someone else will jump in and help out here, and also discuss the haunch forms and why and where they can or should be used? Slainte.
View Image
Richard Jones Furniture
Edited 11/3/2005 1:07 pm by SgianDubh
Thx for the info. Am I wrong though in assuming that a picture/sketch should have been attached to your message? Regarding the "rule of thirds", is that essentially where you divide the width of the stock for the mortise into 3 equal parts and the middle part is how wide the mortise should be? If so, I at least follow that rule. ;)
"100 Years" -- scribbled on the wall by a woodworker to remind him to do his best and as a warranty on his work -- "If anything I make fails in the first hundred years, bring it back, and I'll take care of it. After that, there will be a small charge. (Original purchaser only)"
zombeerose, there is an image of a tenon in the message. I can see it on my monitor. Are you saying it's not showing up on yours? Is it showing only as a box of some sort with a red X in it? Slainte.Richard Jones Furniture
When I view the message I get the "red box with 'x'" (failed IMG). It has the property URL http://us.a1.yahoofs.com/users/435bb61az1fbd6c90/790b/__sr_/3e65.jpg?phyDdaDBeqnouxpc
-robert
Nope - no image...Firefox doesn't even show the red X but IE does.
"100 Years" -- scribbled on the wall by a woodworker to remind him to do his best and as a warranty on his work -- "If anything I make fails in the first hundred years, bring it back, and I'll take care of it. After that, there will be a small charge. (Original purchaser only)"
I don't know why the image isn't loading for you zombeerose. Robert reported it didn't show for him either, but he's put a link to it in his message just before yours. Click on that and it'll take you to the sketch I wanted you to see. Slainte.Richard Jones Furniture
I actually had tried the link and that didn't work. If I had to guess, I would reason the image is somehow tied into when you are logged on. At the moment I am posting this, the link fails.Oh well...
"100 Years" -- scribbled on the wall by a woodworker to remind him to do his best and as a warranty on his work -- "If anything I make fails in the first hundred years, bring it back, and I'll take care of it. After that, there will be a small charge. (Original purchaser only)"
The original property URL didn't work for me, either. I checked again and now it does (for me, using IE).
The property URL I now see is: http://us.a1.yahoofs.com/users/435bb61az1fbd6c90/790b/__sr_/3e65.jpg?phOskaDBU7Ovuxpc -- I have no idea why it might have changed.
-robert
P.S. Nice drawing, worth looking at. Thanks Slainte.
I have no idea why you can't see the bloody image either of you. I loaded it from my British Telecom image host and it shows up on my monitor here at home and shows up on my monitor at my work, so I'm baffled why it doesn't show on your monitors.
I did try to load the image as an attachment to this message so that it would be on Tauntons server and you would be able to click on it, but, and here is another puzzle-- I've just discovered that the Taunton forum attachment facility is non-functioning for me.
This is all too puzzling and I don't have the time to find out what's going on and fiddle with it.
It was just an image of typical tenon layout and proportions that can be found in any half decent woodworking book anyway, and probably hundreds of similar examples can be found by doing a Google image search for tenons. Slainte.Richard Jones Furniture
Not sure either.
Thx for trying and Thx for the advice!
"100 Years" -- scribbled on the wall by a woodworker to remind him to do his best and as a warranty on his work -- "If anything I make fails in the first hundred years, bring it back, and I'll take care of it. After that, there will be a small charge. (Original purchaser only)"
ram...does not work for me using either Firefox or IE..."page cannot be displayed"
Wide joints are where double tenons are called for, as it lessens the cross grain force. Split your 3" tenon into two 1.25" tenons (with a gap between them). Haunching the top is also a traditional way of adding strength to the leg.
Don't go shoulderless unless the table is light. Coffee tables usually aren't, so keep the shoulder for the tenon. You'll be glad you did when the party comes along and people are dancing on the table...
You'll be glad you did when the party comes along and people are dancing on the table...Can I be invited?
Dang - you're right about the people dancing on top...so much for that table ;)
"100 Years" -- scribbled on the wall by a woodworker to remind him to do his best and as a warranty on his work -- "If anything I make fails in the first hundred years, bring it back, and I'll take care of it. After that, there will be a small charge. (Original purchaser only)"
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