Table leg thru tennons?

[Dave Rosner]

Hi - I’m building a small side table for the moms and it’s pretty basic with a square top and a smaller square base. I’m thinking of four square angled legs come from base into top. To give the top some visual interest I’m wondering if I can do through mortises into the table top. So after staining there would be four square in each corner where the legs come up.

ive done thru tennons before but never got them perfect and they didn’t need to be. For this I’ll need to be spot on or else it will show prominently on the table top. Was thinking I cut the tennons on the 4 legs first and make them a little longer so I can cut flush. Then with carefull layout under the table top I’ll cut my 4 mortises slightly under the lines. They won’t be big so I’ll use my drill press to hog out most of it and then finish with chisels.

seems too easy - what will i screw up this way and does this even look good? Not sure I’ve ever seen through mortises on a table top...

[Andy D Jones]

I think you've stumbled onto the reason you don't see them often. Too hard to get right.

Through mortises are usually cut from both sides. But if your legs are angled (and the tenons are straight with the legs), then it is hard to locate the top side of the angled mortise.

I would definitly have a backer piece on the top side if you decide to cut through from the bottom.

And, if it doesn't work out right:
1. they will know where to put the doilies
2. learn marquetry and embed decorative inlay around and/or over the tenons
3. veneer the top
3. scrap the top, shorten the tenons, and use regular blind mortices

-- Andy - Arlington TX

[Jim Becker]

If you can do the work, they look will be great. Hint: you can fix gaps invisibly with little micro-thin wedges of end-grain material. When you are done, any gaps you fill that way will truly disappear.

[Paul F Franklin]

I usually find it easier to cut the mortise and fit the tenon to it, YMMV. If you end up with gaps, and Jim's suggestion doesn't work out, you could add wedges to the tenons. Adds even more visual interest and usually closes any gaps on two edges at least. If all else fails, cut the tenons shorter and inlay thin square end grain plugs. Since you are inserting them from the top, you can taper the sides to get a nice tight fit, and no one but you will know they are plugs and not the ends of the tenons. Keep in mind that no one but you will notice small imperfections.

[Richard Coers]

We need more information about the base. Will there be aprons or a case? The reason I ask is if the top is solid wood, it will expand and contract seasonally. If you have aprons or structure between the legs, that structure will not expand in the summer. So the top will expand in it's width and break apart joinery between the legs and structure. I suggest you do a false through tenon with a router inlay kit and mount the top to the structure with table top fasteners to allow movement between them.

[Dave Rosner]

Thanks all for the suggestions!

I hadn’t thought about wood movement good catch. The “legs” will be 2” square I think and the top is 12x16”. So I think movement is not a factor??

Why can’t I mark the tennons from underneath the table once I have those all done. Then chop from under table to top of table? I’ll want to be extra careful for tear out I’m sure. But getting the top and bottom perfectly aligned will be tough if not impossible right?

[Robert Hazelwood]

Movement is a moderate factor on a 12 x 16" top. To accommodate through-tenons you can't have an apron underneath the tabletop, or at least it can't be rigidly connected to all of the legs. You can have stretchers down lower on the legs.

Also if they are splayed legs your layout idea (building the base and scribing the tenon locations onto the top) is not going to work. At least if you use straight tenons and angled mortises. Instead, I would layout the mortises first on either the top or bottom and then use a bevel gauge and square to project the layout to the other side, using a marking knife and not a pencil, and a mortise gauge to keep the mortise widths consistent. Then make straight tenons with angled shoulders to match the mortises. I'd get the top and legs together first and then make all of the other stretchers to fit.

As you can see, while through tenons are challenging enough, making them angled is increasing the level of difficulty many notches.

[Richard Coers]

Thanks all for the suggestions!

I hadn’t thought about wood movement good catch. The “legs” will be 2” square I think and the top is 12x16”. So I think movement is not a factor??

Why can’t I mark the tennons from underneath the table once I have those all done. Then chop from under table to top of table? I’ll want to be extra careful for tear out I’m sure. But getting the top and bottom perfectly aligned will be tough if not impossible right?
The movement between the leg and top mortise fit isn't the issue, it's how that 1/8" that the top will change in width from season to season will effect on the rest of the structure. The only time you can basically ignore wood movement is with quarter sawn lumber or veneered manmade material used for the top. Our son's Godfather built a white oak roll top desk in the winter. The first spring the writing board on top of the right drawer pedestal started out getting stuck and he was unable to pull it out. The next week it split the joints around it and actually shoved the outer side panel out 1/16". How many mortises have you chopped and had a real clean edge on the opposite side? I've never been able to do that in the 47 years I've been making furniture. Maybe you have a better technique. One solution would be to chop and clean out about 1/4" from the bottom, then drill a hole in the middle and use a flush trim bit to develop a thru mortise. Square out the corners with a chisel.

[Kevin Jenness]

Be aware that this construction depends on the top staying flat for stability. Make sure you are using stable lumber that is close to the expected moisture content in service.

I would suggest using a router with a guide collar and template for the mortises and fitting the tenons second. Splayed legs can be done by shimming the template. Tearout can be controlled by mortising from the top and temporarily attaching a waste block to the bottom. The inside corners can be squared up with a chisel.

430188

These multiple mortises were done with a single mdf template, later versions on a cnc router. Tenons were scribed from the mortise locations and cut with a dado set on a sliding table saw.

[Joe Calhoon]

That’s a nice detail Kevin!

[Tom Bender]

Tapered legs will look much better, just 1/2" is enough.

Drill and chop from the top only. Make them slightly undersized and tapered to a bit bigger at the bottom. Fine tune with chisels and rasps.

You could tighten the whole thing up with wedges like is sometimes done on a hammer but you can wedge both ways.

[Mark e Kessler]

I did similar process as Kevin did. Note that I create a 3deg taper about 1/2 down the mortice with
matching wedge.
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[Jim Becker]

Wood movement can largely be accommodated by insuring that the grain of the legs through the tenons is compatible with the grain direction of the top.

[Dave Rosner]

In reading the advice here and thinking about it more not sure why i just don't locate the tops of the mortises (on the top side of the tabletop) and mortise down. While i would want to minimize tear-out on the underside since it won't be visible less than perfect crisp edges there would be ok. So i locate my 4 "squares" on the top and chop down using the tennons to mark my lines. Id have to get my thinking cap on to make sure when i put them upside down i have the right orientation.

My current design is to have 4 legs that are angled like 2 "V"s but without the bases of the V's touching. So 4 10-20degree angled legs from the base to the top. To create the tennons i am thinking making those perpendicular to the base and top - in other words same as if these were straight legs. I haven't done it before but i'm not seeing the challenge in using my miter gauge and dado to create those tennons.

Im sure i'm not thinking about something and this is harder than i think so please challenge away!

[Robert Hazelwood]

Are there any stretchers connecting the legs? That's where you can run into wood movement issues. Each pair of tenons will move closer and farther apart as the top expands/contracts across its grain. If a stretcher or apron is rigidly connecting the legs then you can get problems. That's why you wouldn't put a through tenon on, say, a shaker table.

Sounds like you want to make angled tenons and straight mortises. That's certainly easier than straight tenons and angled mortises, though weaker. If you leave enough meat on the tenon it will probably work out ok, but I would suggest keeping the splay angle conservative.

If you are chopping the mortises with a chisel then you definitely want to work from both sides. Chopping through the bottom can produce gigantic splinters that may not be very hidden. I think you'll regret it. If you're using a router then its ok, I've never had a problem going all the way through with an upspiral bit.

To work from both sides, just make your layout lines on the top, then use a square and marking gauge to transfer those to the underside. Use a knife for the layout as it gives a definitive place for the chisel to go on the final chop, and helps prevent tearout. If you don't have a marking gauge you can use the depth gauge feature of a combination square.

[Jim Dwight]

Loose tenons may be another option. I would use my domino but a plunge router would also do it. The edges will be rounded, however, but you can fairly easily get a tight fit. With a plunge router, I would make a little jig.

[Thomas McCurnin]

Super accurate layout lines, on both sides. Cut almost to the line then use a chisel to finish the final fitting of the mortise, and a chisel or shoulder plane to finish the tenon to fit. The key is cutting almost to the line.