Questions about tapered sliding dovetails

[Winston Chang]

I'm in the process of making a table with the legs attached to a large batten that fits into a sliding dovetail slot. This is inspired by a table from Chris Schwarz's Anarchist's Design book (there's a picture here). One thing I'm doing differently is that the batten in my table is tapered; they're about 3 inches wide and taper 1/16 inch, and are 22 inches in length.

My first question is this: how tight should the fit be? Right now it's somewhat humid where I live, and it's not in an air-conditioned space. My goal is to have the battens friction-fit, without the use of glue, so that the table can be knocked down in the future. I'm concerned that if make it have a good fit now, it'll be loose in the winter.

Here's a picture: the batten currently is about 2 inches shy of the end of the slot, after hitting it with a reasonable amount of force from a mallet.

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Adjusting the fit is pretty simple: I just take it out, plane the edge, and re-fit it. If it's not equally tight at the front and back, then I shave off a little from the tighter side. If I fit it too tightly now, do I have to worry about splitting out the edge of the table? On one hand, there's only about 1.5" of material between the batten and the edge, but on the other hand, the lateral (splitting) forces are distributed over a large area.


My next question is about tapered sliding dovetails in general. It's simple to adjust the fit of these battens, but for a normal sliding dovetail, you can't use an ordinary bench plane to shave down the tail part. What are some good techniques and tools for adjusting the tail and/or slot?

[Jim Matthews]

I would assemble with Slipit or some other tenacious wax if disassembly is anticipated. A peg (under the leg mortice) would confine seasonal movement to keep it from working out of the housed end.

I use a 2 pound "dead blow" hammer for this kind of assembly.
-ONLY- for the last 1/2 inch or so.

Creaking, groaning or cracking noises indicate a pass over 220 grit sandpaper on my granite honing plate are in order.

[Brian Holcombe]

I like to feel where they're loose in the groove, sometimes they'll be tight up at the front or back and loose at the opposite end. Ideal is a consistent fit along the length of the board so that one end does not have a tendency to pull out.

[Phil Gaudio]

"My next question is about tapered sliding dovetails in general. It's simple to adjust the fit of these battens, but for a normal sliding dovetail, you can't use an ordinary bench plane to shave down the tail part. What are some good techniques and tools for adjusting the tail and/or slot?"

I have used a modified Lie Nielsen side rabbet plane with good results. Just add a wedge to the depth stop of the appropriate angle and it does a nice job on the dovetail and socket.

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[Robert Engel]

I wouldn't worry to much about movement as the batten is only a couple inches wide.

I've used a side rabbet plane on dados but not sliding dt slots. But with mixed results, probably due to my own lack of skill.

I don't do a ton of them, for me I've determined it's best to not mess with the tapered tails and just dial in the slider.

[Winston Chang]

I like to feel where they're loose in the groove, sometimes they'll be tight up at the front or back and loose at the opposite end. Ideal is a consistent fit along the length of the board so that one end does not have a tendency to pull out.

The picture I showed is of the second batten I fitted to the top. I learned this very lesson from the first one, and that's why I'm being really cautious with the second one. The other batten is a little loose at the narrow end, and to fix it, my plan is to laminate on a thin strip of wood to the side of the batten and then plane it to fit.

[Eric Rathhaus]

The way I learned it, we tapered slightly one side of the tail/slot to create the friction fit. We used chisels and a router plane.

[Brian Holcombe]

One thing to do is use a very shallow taper. I prefer them to be straight (no taper) but they’re certainly easier to fit with a taper.

[Winston Chang]

I have used a modified Lie Nielsen side rabbet plane with good results. Just add a wedge to the depth stop of the appropriate angle and it does a nice job on the dovetail and socket.

Thanks, that seems like a good technique. Anyone know if the Veritas side rabbet plane can also be used this way? I like the design of it, and it costs less than a pair of LN side rabbet planes, but the curved depth stop.

I also realized that I could use (gasp!) sandpaper glued to an angled piece of wood for fine adjustment.

[Winston Chang]

I wouldn't worry to much about movement as the batten is only a couple inches wide.

Thanks, that's a good point.

[Tom Bender]

Back up a minute and look at the big picture.

The base may not be a perfect fit so that the sliders will not align perfectly with the slots. Then you will have to either pound them together or loosen the fit, or both. And if the table is on an imperfect floor it will bind anyway. You might want to make one of the sliders detachable from the base.