Loose sliding dovetails in winter

[Winston Chang]

I made a table where the legs are attached to a batten, and each batten is attached to the top using a sliding dovetail.

sliding-dovetail-leg.jpg

The battens are 22" long and tapered, so that one end is 3" wide and the other end is 1/16" smaller. When I assembled it, it was during a humid part of the summer and the fit was very tight. I had to hit it with a mallet to get to move the last inch or so. The table was rock solid, even though I didn't use glue on the battens.

Now it's winter and the air is dry, and the battens are loose -- I can slide them out by hand with no resistance, and the table rocks back and forth when it's bumped.

I asked in these forums a while back about seasonal movement and was advised to not worry about it, but it looks like I should have worried about it a bit more.

Any advice about how to deal with the loose battens?

And in the future, if I build something like this again, how should I deal with seasonal movement? I obviously don't want it to be loose in the winter, but I also don't want it to be so tight in the summer that it would crack. I wonder if it would have helped if, in the battens, if I had oriented the wood so that the expansion across the dovetail was radial with respect to the growth rings.

[Andrew Hughes]

My best guess is your sliding Dt that you cut in the top is too close to the edge. On your next one move it in and do change the grain on the male part quarter or rift.
What wood am I seeing looks like Alder or maple.

[Greg Funk]

I think your dovetail is probably just too wide. If you want it that wide it's better to orient the grain vertically in your diagram as you surmised. An alternative would be to make the dovetail narrower. Something like the diagram (not to scale) below.

dovetail.jpg

[mreza Salav]

I have used sliding dovetails but in much smaller cross-grain applications and with glue. These joints are not forgiving at all and slightest change in the dimensions (as you have noticed) will cause in a loose joint. I am not sure why you chose to use that type of connection of batten to top. For table tops I always use mechanical fasteners (screws).

[Andrew Seemann]

Well, your sliding dovetail did exactly what it was supposed to do, allow wood movement with the change of the seasons. And what you experienced is also why it usually is not used in that situation, Typically for a table top, you would use table top hardware like figure 8s or Z clips, buttons or cleats in a groove, screws in elongated holes, or any of the other standard ways to attach a table top to the frame/legs. Tables have been around a long time; most of the details have been worked out. If you don't see tables constructed in a particular way, there is a good chance that it may not have stood the test of time (and the seasons).

You don't have your location listed, but depending on where you live, there may have been no way to make that joint work. It would not fare well where I live, with the extremes between the humid summer and the bone dry winter. As far as advice gleaned on this site, there are places in North America where it probably would have worked just fine; you just aren't in one of those places it seems.

You could permanently fix the top to the cross piece in the center with some screws or dowels, That would keep the top from sliding off, but still allow the top to move with the seasons. I usually do something like that when I use screws to attach a table top. The center gets a normal hole, but the ones not in the center are elongated. It is a pretty table and worth trying to save.

Just chalk it up to learning. I have a pretty significant body of work from about 25 years ago that proved it took me a long time to get the hang of wood movement

[Dan Friedrichs]

Winston, that table looks great - I love both the design and execution of it. Very nice work!

Maybe I'm missing something, but why can't you just add a plugged screw (or such) at the center of the batten? The top will still be free to expand and contract width-wise.

[Brian Holcombe]

A sliding dovetail works best in conjunction with other joinery. As you found they’re not good as the only joints holding a table up.

Use it for what it does best (lets the top move) but make the supports in a way I which they are self sufficient.

Now about sliding dovetails;

Width helps structurally bit as you found the joint loosens with seasonal change. This can be minimized if the joint compresses slightly as it is assembled. If they slip together without much compression they will be loose pretty much forever.

[Brian Holcombe]

Here is a table I made over the summer. The sliding dovetails went in tight, they were about 40" wide and that was some work!

The tenons go into the table top, the sides of the tenons are made with clearance for seasonal movement but the large faces which bear against the end grain in the mortise are made tight (compression fit).

This table is rock solid, myself and my client pushing against the side could not get it to budge. The majority of that strength is in the tenons which enter the top, the table was merely strong prior. The dovetails do help but they're not relied upon to prevent racking movements.

[David Utterback]

Can you glue an inch or two the snug end and let the remainder of the joint move?

[Brian Holcombe]

You can, but then the joint can't be easily taken apart, better to just use a peg or screw in the center.

[Jim Becker]

The simple solution is to drive a pin or screw up from the bottom that simply keeps them from sliding...in the center as noted so that things stay even. The reason you're getting the issue is that the grain direction on the top of the leg is cross grain to the table top. The wood contracts and expands across the grain. Therefore, the male side of dovetail is getting narrower while the female side in the bottom of the table isn't changing size at all in width due to grain direction.

[Winston Chang]

I am not sure why you chose to use that type of connection of batten to top. For table tops I always use mechanical fasteners (screws).

The design was inspired by the staked desk from The Anarchist's Design Book by Christopher Schwarz. In his desk, though, the dovetails aren't tapered, and used he glue on one end of the batten.

[Winston Chang]

Winston, that table looks great - I love both the design and execution of it. Very nice work!

Maybe I'm missing something, but why can't you just add a plugged screw (or such) at the center of the batten? The top will still be free to expand and contract width-wise.

Thanks! I may end up doing what you suggest, though I'm a bit concerned that if I use a screw, the racking motion will cause it to chew up the wood and loosen up over time.

[Winston Chang]

Here is a table I made over the summer. The sliding dovetails went in tight, they were about 40" wide and that was some work!

The tenons go into the table top, the sides of the tenons are made with clearance for seasonal movement but the large faces which bear against the end grain in the mortise are made tight (compression fit).

This table is rock solid, myself and my client pushing against the side could not get it to budge. The majority of that strength is in the tenons which enter the top, the table was merely strong prior. The dovetails do help but they're not relied upon to prevent racking movements.

Fantastic work! Was it assembled by sliding the battens into the top, and the putting that assembly on the legs?

[Andrew Seemann]

Thanks! I may end up doing what you suggest, though I'm a bit concerned that if I use a screw, the racking motion will cause it to chew up the wood and loosen up over time.

You can put a few screws in at the center of the batten. Just keep them within a space within about 3 or 4 inches at the center. There won't be enough expansion/contraction to matter over that distance. You are mostly trying to center the top on the batten and keep it from sliding out. Also/alternatively since the top is removable, you could take the top off, route a groove most of the length of the top and add table cleats on the inside side. You might even be able to put figure 8s in as an option.

Hey, just noticed you are from MN as well. Yep, that design will be problematic here. Just wait until January when the temp is -20F and there is no moisture in the house As you build furniture, you'll need to keep in the back of your mind that summer to winter expansion here can be double what is in some other parts of the country, and certain things just don't work like they do other places. Most folks don't understand how decks can make gunshot noises in winter.