So, you want to cut a tapered sliding dovetail…

In building the bookcase for my current commission I have based the design quite heavily on the boarded design presented in ‘The Anarchist’s Design Book” with a few key departures. Obviously, I’m working in walnut and not pine, but the one that is harder to catch is the subtle joinery switch-up with the back rail and the kick. Instead of butt joints and grooves I’m employing sliding dovetails on each. I chose this route for two reasons: to add mechanical strength to the design and to reduce the number of nails required.

Visually, I like the nails on the shelves (although each shelf is only getting three), but the kick and rail nails seemed to make the unpainted side too busy with fasteners. I wanted a cleaner look, and so instead of nails we have tails.

I’m not pretending to be an expert on this particular joint, just sharing what I’ve learned. If you want to learn how to cut this joint watch this. I can’t lay it out any better than Frank Strazza and I don’t know anyone who can. I should say that the joints in my project are slightly different because they’re aligned with the grain, but the same principles apply. I chose to cut the tails first because there are a few more variables there, and then layout the groove to match. Each joint was laid out using a bevel square and a Sterling Toolworks 1:4 dovetail marker, and after cutting both parts of the joint each was friction fit by trial and error until it sat firmly in the housing.

I didn’t intend to write this up so I neglected to take pictures of the tail being marked and cut, but it tapers about 1/8″ in on either side from the “face” of the joint to the inside. You definitely want a rip filing for this cut and I found it easier to align myself looking at the “face” of the joint and then start the cut on the far side so that I could lay it back into the kerf and make adjustment as I went. Frank Strazza starts his cuts from both ends and meets in the middle. I’m not that good yet.

Treat the shoulders like tenon shoulders which means first class cuts. Chisel a channel along your knife line on the shoulder and finish off with a carcase saw. You should end up with something like this:
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Then it’s time to cut the housings.

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Using a batten again, but this time one with a 1:4 taper planed onto one side, I was able to get a good start on each cut. The challenge is similar to a half blind dovetail in keeping the adjoining surfaces clear of errant saw marks while trying to cut as much of the housing wall as possible. This was easier on the kick because the dovetail intersected the dado.

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On the stopped housings I found it easier to clear them by using a small chisel to remove the waste to depth at the end of the groove and then work back toward the opening with a bevel-down chisel/mallet technique.

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On the others I just lined the chisel up with my marking gauge line (bevel up) and gave it a smart whack. I followed that up working bevel down from the opposite side and I was able to remove the waste in short order.
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In both instances I cleaned everything up with my router plane.

And there you have it. A nice mechanical joint to strengthen an already great design.

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A couple of notes:

  • Make sure to take a good length measurement directly from your shelves in a dry fit scenario and then size your tails such that the visible face of the kick and rail are equal to this measurement. This is crucial when everything comes together.
  • I used a dovetail saw to cut both the tails and the housings because the housings were rip cuts. If you’re working across the grain a carcase saw is the better choice.

 

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8 Comments Add yours

  1. Brian Clites says:

    Awesome work Jim. Was it just because you wanted the challenge, or did you have another reason for choosing the sliding tails over a simpler dado joint?

    Liked by 1 person

    1. A little of both. The dovetails give the nails a little backup.

      Liked by 1 person

      1. Brian Clites says:

        Really? I am having trouble picturing exactly where the Czar on the bookcase. If the kick is at the bottom, then the mechanics of the sliding tail actually do not add any strength over the mechanics of a dado…because the wedge is going into the case, so it’s really just about glue surface, right?

        Like

      2. Brian Clites says:

        Ahhh. I see now James. These are full sliding tails, and the structural benefit is created inward. Thus your choice to put one on the top and the other on the bottom follows perfectly — reducing the strain on all the nails in between. Sorry I missed the orientation on my first few readings…

        Like

      3. Yep. With those two joints it’s practically free standing with no nails. The nails and glue on the shelves will just reinforce the whole thing and the back will make it rock solid.

        Liked by 1 person

  2. Brian Clites says:

    “Where these are” (Not “wear the czar” … I’m all thumbs on my phone)

    Like

    1. jdsteed16 says:

      i’m actually quite taken with ‘wear the czar’.

      Liked by 2 people

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