coffee table feedback

[Mike Steinhilper]

Ok, this is not easy to describe without a pic, but I'll try. I have the legs and aprons completed for my coffee table. I would like to have a shelf on the table right above where the taper on the legs start. The table is about 18" high. Any recommendations on how to join the shelf without adding another apron? The legs are 1 1/2" square. Is there enough material to have a 3/4 morise? Thoughts?

[Don C Peterson]

I built a hall table a few months ago where I had the same problem. I wound up using kind of an "H" stay configuration with cross pieces on the sides into which a sturdy "beam" fit with through wedged mortise and tenon. Since my hall table was so long (6ft) I put a support foot midway on the beam.

http://www.sawmillcreek.org/attachment.php?attachmentid=74608&d=1194133007

The other idea I toyed with involved bending two "C" shapes which would be attached back to back and the ends mortised into the legs at an angle. Although this would have provided nearly invisible support for the shelf, I decided against it because I'm not set up to do steam bending. I think it would have been cool though...

[Andrew Nemeth]

Mike,

I have approached similar situations two ways.

If the load is going to be really light you can notch the corners of the shelf and dowel it in place. The strength of this joint will be determined by the shelf thickness and what the maximum sized dowel it can accept. It is important if you go this route to use breadboard ends, or something similar, on your shelf panel to allow the shelf to expand and contract independently of the legs and apron above (the end aprons grain will be running across the grain of the shelf). The notches would actually be cut on the breadboard end not the long grain of the shelf. If you don't allow for this the joints are likely to come loose or the shelf is likely to split.

The second approach, and the one I prefer, uses an apron that is mortised into the legs. I prefer this because it is provides rock solid piece when I am done and it has the benefit of preventing the shelf from sagging. When I do this I cut a groove on the back side of all of my aprons and glue blocks with a mating groove on the table top. I then insert splines in between the two to hold everything together. With this method you do not have to use breadboard ends if you make sure that you leave a little bit of a reveal between the shelf and the legs.

If you are at all confused by my description and want want to know more I would be happy to take some photos and try to explain it more thoroughly.


Hope that helps,

[Mike Steinhilper]

thanks! Andrew, do you glue your spline or does the shelf float in there? would it be too much trouble to post a pic?

[Danny Thompson]

Here is a bench I made with a 3/4" square tenon notched into each corner of the shelf leaving a 1/2" shoulder on all sides of the tenon and with a corresponding 3/4" square mortise in each leg. The legs are slightly larger than yours. They are 1 3/4" square and the shelf is 1 3/4" thick. Sturdy as they come.

[Andrew Nemeth]

Mike,

I do not glue the splines in place so that the table top (or shelf) can "float". Technically, you could take the table top (or shelf) off and put it back on again although it is a tight fit and there is no slop. When I mill the groove into the stock that will become the blocks I make the slot slightly closer to the table top than the slot in the apron (I use a piece of tape along the fence to provide the proper offset). This offset helps pull everything tight once the spline is inserted. I find it easiest to actually assemble the legs and apron first. Second, insert the splines into the slots and add the blocks. Then I glue and clamp the top onto the blocks. I will snap a photo tomorrow when I am near a piece that is constructed as I mentioned.

[Mike Steinhilper]

Danny, do you compensate for wood movement in your system? I'm afraid if that shelf panel shrinks and it's glued in the leg mortise, it would split. Or maybe you don't glue?

[Doug Shepard]

This one had M&T's into the tapered legs about 5/8" deep
http://www.sawmillcreek.org/attachment.php?attachmentid=14924&d=1105799654

[Roy Wall]

Mike -

This has a BE Maple shelf sitting between two side rails. Notice the double mortises just above the taper (on the legs in back). These were 1.5" square legs also.....

[Danny Thompson]

I did glue. My thought was that the majority of expansion would be horizontal rather than vertical, so the shelf may have a tendency to push the legs apart. However, the seat should expand and contract at the same rate, so the legs should move freely with the movement of the shelf and seat. I should be okay there, right?

I guess the risk is that the shelf and its tenon may expand vertically while the mortise may expend horizontally. I have to admit I did not compensate for this possibility. On the other hand, do I need to? My reference point is they way mortise-and-tenon joinery is used in frame-and-panel construction. The stile mortises are glued into rail tenons, or vice versa, even though the wood is oriented in different directions. Does that sound right?

[Sam Yerardi]

Mike,

You've got some good suggestions in these posts. Another approach I thought of would be to make each corner an integral part of the legs, i.e., see the attached bitmap. I was wondering if a mortise/tenon or dowel from the end of the upper part of the leg, through the shelf, and into the bottom part of the leg might work. I think it would be very strong.

[Mike Steinhilper]

Danny, I'm no expert on wood movement. I would think you'd be fine, but I don't know. I just hear a lot about it. I guess I'll become an expert when it ruins one of my pieces!

Roy, that is looking like the simplest solution so far. How did you join the shelf to the side rails?

Sam, that idea is intriguing. So if I understand correctly, do you suggest cutting the legs and using a tenon running through the shelf to re-join them?

[Sam Yerardi]

Yes. You could do a dowel or round tenon insert into the bottom leg, come up through a hole in the corner and then into a mortise hole in the top part of the leg. The difficulty will be centering the hole but since it is a square that you're working with, it wouldn't be that much. You leave the edge of the shelf flush with the side of the leg or do a small reveal but stay inside the edge of the top.

[Thom Sturgill]

I think most people get over-anxious about wood movement. I think the main problem in a joint would be shrinkage causing the joint to open. With modern glues, if the wood is worked at the right moisture content, this should not be an issue in the joint area itself. And as mentioned above, if the shelf grain and the top grain are in the same direction, then the movement at the two connection points to the legs should be about equal if the top and shelf are of the same species of wood and free to move.

If the top is floating and only loosely connected, as is normal in a large table, then I would probably do the same for the shelf. If it is fixed, as is often done on small tables, then again, do the same on the shelf.

[Roy Wall]

Roy, that is looking like the simplest solution so far. How did you join the shelf to the side rails?



This was joined by making a wide tenon out of the shelf section -- (be maple), then cutting a mortise on the inside of the rail. The mortise is about 1/2" longer than the tenon; and I glued the middle 3" of the tenon. This gives the joint some room to seasonally expand if needed.

I've also done this another way with mortising BOTH ends and using a long, floating tenon....just gluing the center section again....same effect.

[Danny Thompson]

Nice photo, Roy.

[Mike Steinhilper]

all good ideas... thanks. Roy, how thick is your shelf? mine is only 5/8" and i'm not sure i have enough material for a decent tenon.

[Danny Thompson]

Could always forgo the tenon in favor of embedding the full 5/8" in a dado in the leg.