How to make sliding dovetails

Sliding dovetail joints are very useful in a number of furniture making applications.  They are sometimes used instead of dadoes to join shelves to cabinet panels, or to join cabinet panels to each other.  Sliding dovetails are also sometimes used as drawer slides - and are better than "square" slides because they don't allow the drawer to lift away from its travel path. 

I have been afraid of dovetails for a long time, mostly because of the apparent difficulty of getting a good snug fit.  But sliding dovetails offer up a chance to make a dovetail without worrying about making LOTS of dovetails, as you would with a dovetailed case edge.  Making long sliding dovetails isn't easy, but it's totally doable, with the right power tools.

The first step is to mill the two workpieces to be joined, flat and square.  Next, pick the location of the "female" side of the joint, and plow a centered dado along the path of the joint using a router and a straight bit.  Make sure the dado is wider than the bottom of the dovetail bit, but not so wide that the dovetail will leave too little stock.  Plow the dado s deep as you want the joint to be  - or just a hair shy of that depth.


Here's how to make a centered dado: set the bit as close to the center of the stock as you can.  Make a pass, then another pass referencing off of the opposite edge of the work.  Now you have a centered dado.

Next, chuck in a dovetail bit to the router.  Set the depth of cut to exactly - or just proud of - the depth of the dado you just cut.  Route out the sides of the dado with the dovetail bit in pairs of passes.  Now you have the female part of the joint.

DON'T CHANGE THE HEIGHT OF THE BIT.

Using the same bit depth, switch to the male workpiece.  Here, you'll be shaving away stock from both sides of the work with the dovetail bit, until the male side of the joint just slips into the female side.  take light passes so you don't tear out the side of the dovetail.

TIPS:
- sometimes the joint only goes in part-way.  Make sure the work isn't coming off your fence while routing both the female and male sides of the joint.  A featherboard on a router table can help ensure the joint is consistently thick on both sides.

- if you move the work out of a climate-controlled shop into the real world, be prepared for wood movement.  Make your joint loose enough so it doesn't crack in high humidity, or get too loose in a dry environment.  If you need the joint to make a rock-hard, wiggle-free connection (such as I use in my Wine Bars from Wine on Deck), I recommend shooting a dowel through the joint at one or more points along its length.  This will lock the joint up, preventing wiggling, even if there is some room for wood movement in the joint.

- all power tools leave marks, no matter what.  You can reduce the size of the blade's "wave" pattern by making slow passes with the dovetail bit.  But if you take too many passes over the same surface at the same depth, you can actually create more peaks than if you just take one slow, light pass. Strange but true.

- to remove tool knife marks, sand the joint with a sanding block cut at the proper angle so it can get to the entire joint surface on both male and female sides.  I have also used a block plane, but it's hard to get into the corner of the joint without a dovetail plane, which I don't own.

Good luck!

-isaac