Basic Joinery Question

[David Wadstrup]

Hi,

I have a VERY basic joinery question that I was hoping someone could answer for me. I'm building a small stool. The top will be 26" x 10.5". It will be 12" tall. The design is simple -- 4 legs joined by 4 rails. My question is in regards to joining the legs to the top(it has no skirt.) I intended to dovetail the legs directly to the top, but have started to get nervous about wood movement. Should I be? Wouldn't the wood movement across the grain become a problem? If yes, what kind of joint would be appropriate here? Would half-blind dovetails be the solution(so I could leave an unseen extra wide tail to allow for the seasonal expansion and contraction of the top?) I'd really appreciate your help. I'm trying to expand my joinery knowledge and technique and don't know how to proceed.

Thanks!

David

[Zach Dillinger]

Do the edges of the top overhang the skirt at all? If you are dovetailing it in, I assume they are flush. In either case, I would advise against dovetailing the top in. You would be creating a "ticking timebomb", in which it would just be a matter of time before the top splits, or worse expands to the point of destroying the leg to rail joinery. The whole thing could simply self-destruct. For a simple stool like you are describing, I would have an inch or so overhang, and then use those metal figure-8 table top connectors. The overhang will allow you to hide any expansion or contraction (if you put the top flush, it will rarely be flush over the life of the stool), and the connectors have enough "wiggle" to accomodate any movement. You didn't say what species you are using, so the movement could range from substantially noticeable to barely noticeable over a 10.5" wide top.

Failing that, you could simply nail the rails to the top, or you could screw the top to the rails from the inside, at the middle of the top. This will allow for movement as well. Wood to wood joinery isn't the best choice for a top and you rarely see it. You could work out some sort of sliding dovetail joint, but for a small stool I wouldn't bother.

[Prashun Patel]

Legs directly into the top? I'd turn round tenons on the end and wedge them thru the seat.

[David Posey]

You wouldn't need them round. They could be square or rectangular and you could still wedge them in, sort of like with a foxtail tenon, although it could go all the way through. I get the impression the OP's design has the legs at the edge of the top though, and this wouldn't work there.

[Tony Wilkins]

Thought about it and my suggestion didn't make sense - carry on.

[David Wadstrup]

Thanks for all of the help. I really appreciate the feedback and guidance. The top of this stool will not have a skirt. It is simply a flat board. There will also be no supporting upper rails that the top will rest on -- just the 4 lower ones. This is why I'm unable to attach the base to the top with screws. And, yes, the legs are intended to meet the top on it's outer edge. I'd really love to avoid any kind of fastener here -- it's kind of my goal, if possible. Is there no wood to wood joinery method for attaching legs to a top? In case it makes a difference, I'm building this with Ash. Thanks again!

[Zach Dillinger]

David, given the design constraints and the lack of top rails, I'm having a hard time visualizing a wood to wood joint that will work for you. The tenoned-and-wedged legs will be tough to do, since the edges of the top will be flush with the legs. I could see this method splitting the top when you drive the wedges or with seasonal, especially in a split friendly wood like ash. Plus, if you lock all four legs at the bottom and the top, your stool will do its level best to destroy the joints where the bottom rails attach to the legs.

How thick is the top board? You might be able to cut a stopped sliding dovetail across the grain, and cut the male part of the dovetail into the tops of the legs, glue the front into place and leave the back legs free to move. This will only work if your top is of sufficient thickness, obviously.

I have no experience with woodworking in Brooklyn, so I don't know what kind of wood movement you get there. I'd be worried about this design, though, without top rails.

EDIT: Thinking more about this, it sounds a bit like a mini-Roubo workbench. Do I have the design properly visualized?

[Richard Line]

If I understand your design correctly, you will have the legs joining the top on the edge of the 10.5" width and the legs tied together with rails a couple of inches up from the bottom, probably with m&t joints. Your plan is to join the legs to the top with dovetails, either through or half blind.

If that description is about right, then I suspect the legs and dove tails would be placed 1 inch or so in from the long edge, making them something under 8 inches apart. The amount of movement over 8 inches should not be a lot, especially if the stool will be inside. There will also be some flexibility from the legs that will help accommodate the movement of the top, unless those legs are massive.

The weak part of the design will be the legs (dove tails) pulling out of their sockets due to racking in the long direction. Glue will certainly help, but how much and for how long? You might consider pinning the dove tails with dowels/pins running across the sockets starting from the edge of the top or even a glued in pin that runs from the leg into the top would help. If you go with pins, an open mortice and tenon joint maybe as good as a dove tail.

[David Wadstrup]

Zach and Richard,

Yes, the design is much like the Roubo I just built. With the exception of the top rails and the split top. The top is only 1" thick so the more I think of it, the more I come to realize that half blind dovetails would not work. I had thought about handling this leg to top joint with wedged mortise and tenons, but if I'm not wrong, I think I'd have the same problem with restricting movement and causing the whole thing to self destruct as I would with the dovetails. So, perhaps there's just no way around putting in 2 short top rails after all, and bolting the top to these??? Damn! I really was hoping for a fastener free design.

Thanks for the help,

David

[Tom Vanzant]

David,
It sounds like a small version of Chris Schwarz's Roubo bench. The dovetails would be into the outer edges of the seat, with shoulders on the legs bearing against the bottom of the seat. The 1" thickness of the seat should be ample. 1/4" dia dowels thru the dovetails into the seat would provide a "belt and suspenders" security net for the joints.
Tom

[Jim Koepke]

David,

I made some saw benches that may have the joinery that will work for your stool.

234298

They are half laps on the legs and the top surface. The smallest one is used for a stool in our home. The legs angle for the smallest one are at 5º in each direction.

There are a lot of possible variations on this. One of my benches has the sides beveled at the same angle as the legs. The tops of the legs are all flushed with the top of the surface. They can also be made flush with sides or stand proud just a bit.

Here is the link to my post on making my first saw bench:

http://www.sawmillcreek.org/showthread.php?146777-Saw-Table-Project

jtk

[Zach Dillinger]

David, if you put in those top rails, you could use dowels to fasten the top (no metal fasteners). Drill down through the top so that the holes are centered on the top. This will allow the top to move in both directions without impediment, but will still fasten the top securely.

[Jim Matthews]

If you're willing to cut the top and relaminate, your joinery will be MUCH easier to accomplish.

If you're fitting the legs into a solid top, round tenons in round holes are dead simple to handle.
Getting the legs to line up isn't trivial - but a couple of bevel gauges can help you keep track.

There was a FWW article on building chairs with a reamer that showed the set up.