Joinery Question from a Newbie--3-way intersection

[Brad Root]

So I am pretty new to woodworking (I have made a storage banquette and my workbench so far). For my third project, I am going to make a table base for a new kitchen table. The space in our kitchen is tight, so I need a compact design (30" x 60--65") with plenty of leg room. In order to make leg room on the ends, I am going to have bottom stretcher that will also provide table legs at each end as was done in this picture I found online:trestle_table_picture.jpg.

For my table, however, I discovered that I cannot spread the legs out as was done in the above photo. Instead, I really need to have my table legs in the middle so that the stretcher and the table feet would all intersect. The joint for this intersection of three boards is my problem.

I have designed a tentative joint in which the stretcher (2" wide, 4" tall) and the table feet (2.5" wide, 3" tall) would be joined by a lap joint. The top half of that lap joint (the stretcher part) would also be a through tenon that goes through the table leg (2.5" deep, 3" wide). The table leg would then go around the stretcher and end in a double through tenon that connects it to the table feet.

I made the joint in Sketchup. Here are some images of the joint apart and together:
From Above: Root Joint for Trestle Table--Apart.jpg
From Below: Root Joint for Trestle Table--Apart from Below.jpg
Together: Root Joint for Trestle Table--Together.jpg

My question is: does this look like a viable joint, or have I overlooked something. I like it because I am laminating the feet and legs from smaller stock, so the entire joint can be cut on a table saw.

Here is the sketchup file as well: Root Joint for Trestle Table.skp

[Frederick Skelly]

Welcome to The Creek Brad!
I'm impressed with the way that joint fits together. It's elegant, for sure. I take it you're an Architect or Engineer? I can see how everything fits mechanically - that works. I'm concerned about the long term viability of the glue joint between the green part and the blue part. If I'm not cross-eyed, it looks like you're gluing end grain (blue part) to long grain (green part). It seems like you want that part of this joint to hold very strongly because it "locks" the rest of the joint.

My normal approach would be to add some sort of additional reinforcement to help lock that joint, but just now I don't see how you could insert a pin, etc perpendicular to the joint to lock that blue/green intersection. You could perhaps insert a wedge from the bottom to give you an additional mechanical lock, but I can see several negatives to that. Admittedly, I might be overly concerned here - I just haven't had good luck (long-term) gluing end grain to face grain.

Edit: Making this on the tablesaw and laminating the parts is a sharp way to fabricate this. I was concerned about that and missed that in my original response. I wouldn't have thought to do that.Thanks for the idea.

Look forward to seeing pictures when you get her done!
Fred

[glenn bradley]

Welcome.

Similar joinery challenge here which may add to your ideas. Or jump to 8:21 in Episode 1.

[Brad Root]

Dear Frederick,

Thanks for the feedback and the welcome! I am actually a history professor, so I have literally no design background whatsoever. Being new to woodworking, I am a bit confused about the end grain to long grain issue. Is this a matter of the shape of the tenon (more of the glued surface being end-grain to long-grain)? Should I make the tenons square (3/4" on all sides), or do I really need to have the rectangular tenons with the longer edges facing the long grain of the mating board?

[Brad Root]

Thanks for sharing the video and the welcome! That's probably the neater way to accomplish this joint. I'm just not sure I trust myself to rout a mortise that only goes halfway through the feet. I just inherited a router (no edge guide) and am not very comfortable with it yet. I will have to watch the whole sequence of videos later because I think you are right that I can pick up a few things from it.

[Gene Davis]

Consider doing things the way George Nakashima did with his "conoid" model dining table. Bring the two legs onto the bottom stretcher away from the intersection of stretcher with the foot bars.

My Sketchup model has the joinery modeled. Check it out.

[Brad Root]

Thanks! I really like that! That might be the simplest solution

[Lee Schierer]

The strongest joint will be with the grain in each piece parallel. The next strongest joint is edge or face grain at 90 degrees. The next strongest joint is end grain meeting face or edge grain. The weakest joint of all is end grain to end grain.

[Frederick Skelly]

I am a bit confused about the end grain to long grain issue. Is this a matter of the shape of the tenon (more of the glued surface being end-grain to long-grain)? Should I make the tenons square (3/4" on all sides), or do I really need to have the rectangular tenons with the longer edges facing the long grain of the mating board?

Hi Brad,
Looks like Lee explained the relative strength of various joints and it sounds like some of the guys have steered you to other ways of joining these boards. So I'll leave it at that. If you still have questions on my thoughts, just drop me a "Private Message" (PM) and I'll try to help.

Best of luck,
Fred

[Brad Root]

So I showed several mock-ups to my wife of the table with the legs and feet meeting the bottom stretcher at different points. Unfortunately, she does not like the look, so I am back to finding a way to make the 3-way intersection described in my original post work. I put together a router table, and have been practicing making sliding dovetails, and I think that might be the answer.

For the Bottom, I want to have the feet and the stretcher (all 3" tall) connect to the legs with sliding dovetails (all 1/2" deep and 14 degrees) that go almost the full height of the feet (probably 2.75" tall). I have attached a sketch of the overall table design, and a color-coded diagram of the dovetails.

So here are my questions:

1. Will this work, or am I still in danger of having a joint fail because of grain orientation?
2. Are 1/2" dovetails deep enough for this application? I am having trouble finding guidelines on dovetail depth. I inherited a 1/2" dovetail bit, so if I can make that work, I would like to do so.
3. Should I glue the dovetails?

Thanks in advance.

-Brad

Root Trestle Table Design.jpg
Root Trestle Table leg-foot joints.jpg

[Jerry Miner]

Might work. Looks weak to me. If I were doing this, I would skip the sliding dovetails and cut half-laps in the foot-to-stretcher, and a double tenon at the bottom of the leg post (thereby keeping continuous material in all the parts and decent long grain-to-long grain glue surface):

Table Leg Joint 2-21-16.jpg Table Leg Joint [2] 2-21-16.jpg

Might also add wedges in the tenons

[Nicholas Lawrence]

I don't know that you need that bottom stretcher unless the boss just likes the look. If your table legs are properly attached to the top you should not need that stretcher, and if you get rid of it you will have more room.

[Frederick Skelly]

Might work. Looks weak to me. If I were doing this, I would skip the sliding dovetails and cut half-laps in the foot-to-stretcher, and a double tenon at the bottom of the leg post (thereby keeping continuous material in all the parts and decent long grain-to-long grain glue surface):


Might also add wedges in the tenons

I agree with Jerry, Brad. The half laps will be much stronger and I'd also wedge the tenon as he suggests. (As is, I'm concerned the "corner" between adjacent dovetails may crack when she drags this table out of the way to sweep/mop.)

Good luck!
Fred

[Marty Schlosser]

I'm with Jerry and Brad, especially as it relates to the strength of the joint. I was a bit concerned with your first iteration, that there was simply not enough tenon area to be strong enough. Jerry's design solves that dilemma, in my mind at least.

Regarding the stretcher, have you considered placing it higher up on the legs? That'd give you more foot room, wouldn't it? Just a thought...

I agree with Jerry, Brad. The half laps will be much stronger and I'd also wedge the tenon as he suggests. (As is, I'm concerned the "corner" between adjacent dovetails may crack when she drags this table out of the way to sweep/mop.)

Good luck!
Fred

[Brad Root]

Thanks to all of you for the insightful responses! I was worried about the Dovetails, and I had not really considered the problem that Frederick pointed out the corners of the joint.

Jerry, that's a much better idea than either of mine! I think I am going to go with your joint (though I will have to practice it since I have never done a wedged tenon). May I ask where you got those images (I would like to see the whole table in that mock-up to see how the top joints are done as well)?

Nicholas and Marty, I have considered removing or raising the lower stretcher, but my wife and I both think it adds visual balance to the feet sticking out at the ends. Neither of us likes having the stretcher float, so we decided to go with stretchers at the top and bottom. The current setup provides 13.5” of room for the feet, and I am hoping that will be enough (I will have to place a board on the floor below the current table to see if it does interfere with foot room).

This is probably a stupid question, but I am going to ask it anyway just to be safe: how would I go about making Jerry's joint? I assume that I would glue the half lapped boards together before cutting the mortises. Is that correct?

Thanks again!

-Brad