M/T leg into tabletop question

[James Biddle]

I'm building a coffee table where the top is a 3/4" thick piece of freeform curving zebrawood and the wenge tapering legs are 1-3/4" x 4" at the top. The design calls for the legs to attach directly to the top and I'm thinking M/T would give me the strongest joint. A couple of questions:

What size would you make them?

I'm planning on using a Festool plunge router on a guide rail to cut the mortices. How would you make the tenons?

Is epoxy overkill for glue or would you recommend something else?

Thanks for your help. James

[Greg Sznajdruk]

James:

Not quite sure what you are asking. The top is 3/4" are you intending to mortise the top? Do you intend for the tenon to show through the top?

Greg

[James Biddle]

Yes, the mortise will be in the top and I do not want the leg tenons to show through.

[Greg Sznajdruk]

James:

That leaves the mortice less than 3/4" even at 1/2" the tenon has very little mechanical support. How big is your table top?

If this is what you want to do would adding stretchers between the legs be in keeping with your design? Stretchers would add additional bracing to the legs.

Greg

[James Biddle]

Aprons or stretchers aren't an option on this design. If additional bracing is necessary, I would need to add it inboard of the legs (at the top) so that it will not be seen in the finished product. The problem is that since the top is a freeform design, the legs do not line up and lend themselves to easily adding aprons or stretchers between the legs for additional support.

[Greg Sznajdruk]

James:

You have a real challenge on your hands. Do you have any photo?

Greg

[James Biddle]

Here's what I'm up against. Sorry about the crude design.

[Dan Oliphant]

James, to use the concept that is shown in the drawing my suggestion would be as follows;
Leave the tennon as long (in length) and as wide as possible without making it visable, Minimal shoulders.
Pre drill (and counter bore) two pilot holes per leg in the top (don't panic yet!!)
After the legs are glued, install the wood screws then plug the pre drilled holes with bungs. The bungs must be the correct grain pattern and size to properly match the hole.

[James Biddle]

James, to use the concept that is shown in the drawing my suggestion would be as follows;
Leave the tennon as long (in length) and as wide as possible without making it visable, Minimal shoulders.
Pre drill (and counter bore) two pilot holes per leg in the top (don't panic yet!!)
After the legs are glued, install the wood screws then plug the pre drilled holes with bungs. The bungs must be the correct grain pattern and size to properly match the hole.

Dan, that was my first thought. My question is: what are the odds that I can hide the sharply contrasting grain of zebrawood? I can pull a plug from the hole and reinsert it (if it comes out cleanly), but the filler in the drill bit kerf (is this a real term?) would also have to be matched. I'm thinking this would be difficult.

[Richard Wolf]

I think you should attach plates to the top of each leg and then screw the leg plates into the table bottom. This would give you alot more surface area to glue and screw.

Richard

[Scott Vigder]

First, I do think epoxy is overkill. Fresh yellow glue, properly applied, works great.
Second, can you add one inch "wings" to the legs where they attach to the table. Each wing would surroung the leg, in effect creating a mortise. I would mortise into the table top no more than 1/2 inch. Glue/screw the wing to the tabletop, then to the leg (with proper clamping). The wings would help create surface area to absorb the lateral forces.
Good luck with the Zebrawood.

[Dan Oliphant]

What Richard and Scott suggest would also work well. My comments are based on using a streight or tapered plug cutter that is matched to a given drill size. Matching the grain should not be that big an issue, that is based on the experience I have had with zebrawood.

[Don Baer]

James,
I'd use floating tenions about 2/3 of the size of the legs. I'd also use the yellow glue of your choice. Thats just the way I'd do, it doesn't mean it's right.

[glenn bradley]

I think MR. Wolf is onto something. The engineering challenge is one of joint strength to lateral stress (I'm a network engineer, not a P.E. so large grain of salt required here). The amount of area for the top of the leg just doesn't seem like it will provide enough lateral strength for this table to last very long. Good luck with your challenge.

[Chris Mann]

I've made tables similar to that. I epoxied threaded rod into the legs and used a haefle expanding nut in the top which locks in place when the leg is screwed in. Everything is holding just fine (but my table has 9 legs).

For your situation I'd probably epoxy a metal plate into a recess in the table and tap it, then screw the leg into that. If you decide to go with regular mortise and tenon, I'd split the tenon in two and use epoxy to glue it in. Something like each tenon 1"x1 1/2"