A Box Joint with Variable Width Pegs
By Ronald W. Leigh
September 24, 2015
Copyright © 2004 Ronald W. Leigh
Here is a method for making box joints with variable-width pegs on the same joint. It is an easy method which uses something every woodworker already has, a table saw. No expensive jig required. The picture below shows one corner of the frame of a medicine cabinet. Notice the wider pegs near the top and bottom edges and the narrower pegs in the middle.
You have probably seen various box joint jigs in catalogs and on the internet. They
come in various sizes (1/4", 3/8", 1/2", etc). Some are quite
complicated, with fine-thread lead screws for making precise adjustments. Perhaps
you have also seen Norm Abrams' program called New Yankee Workshop in which he
demonstrates his own shop-made jig for cutting box joints on a table saw. But one
thing all these jigs have in common is that all the pegs on a given joint are the same
width. Even though some jigs are "adjustable" (in that they can produce
pegs of various widths), all the pegs on a given joint will be the same width.
The method described below will produce pegs of different widths on the same joint, and it doesn't use a jig or a dado! All it requires is a table saw with a miter gauge large enough to allow you to stand a board on end and guide it past the blade.
I don't claim that the method described here is a new method, but I have never seen this method mentioned in the literature or on the web.
For both aesthetic and structural reasons, it is best to have an odd number of total pegs, with wider pegs near the edges of the boards and narrower pegs in the middle. Often, the edges require extra machining (such as a rabbet for the back of a cabinet or a round-over on the front), so it is an advantage to have the pegs at the edges sufficiently wide.
In this example of the procedure, we are joining two boards cut to a desired length from nominal 1" x 6" stock. Actual dimensions, of course, are 5½" for the width, and ¾" for the thickness. We will create an 11-peg joint.
STEP 1
Start with boards that are flat and square at the ends, and are exactly the same width. This makes the following setup steps easier, and avoids extra planing or sanding after assembly.
STEP 2
Set the depth of cut on your table saw equal to the thickness of the boards (¾"), or perhaps 1/64 more.
STEP 3
Select the two boards that will form one joint and stack them together. Mark the ends of these boards to indicate the width of each successive peg/opening, and place an "X" in each section to be removed.
Board A, has 6 pegs with a peg at each edge, while board B has 5 pegs with openings at each edge. Starting at the outside edge, the width of each successive peg gets smaller until you come to the middle peg, then they each get larger again as you proceed to the opposite edge. In our example, the widths of the first 6 pegs (starting from the outer peg at either edge and going to the middle peg) are: 11/16, 19/32, 1/2, 7/16, 3/8, and 5/16. Of course, you can use any number of pegs and make them any width you want.
If you are creating a cabinet in the European style (no facing frame), use Board A for the vertical. The pegs at the outer edge of the vertical board will give an appearance from the front that looks somewhat like the standard stile/rail arrangement. If you are going to add a facing frame, or if you are creating a box, it makes little difference.
STEP 4
Clamp the boards together so board B is offset to the right by a distance of one kerf. Place the clamp far enough from the end so it will clear your oversized miter gauge.
To get this offset distance just right, you will want to make spacers to be used as shown above. Don't attempt to set the offset by measurement. Also, don't attempt to determine the kerf by measuring the width of the blade's teeth since tooth "set," blade-table misalignment, and blade wobble will all widen out the actual kerf. Instead, make a test cut on the end of a scrap piece of the same stock you are using for your project. Then create the two spacers. Each spacer should be just wide enough to hold itself firmly in the cut. If it falls out when you let go, it's too narrow. If you have to force (pound) it into the cut, it's too wide.
After aligning the boards with the aid of the spacers, and after clamping the boards, set the spacers aside.
STEP 5
With the boards still clamped together, mark the kerf locations on the end of the boards, making sure each kerf passes through two sections marked with an "X." (The kerf should not cut into any unmarked section.) Then transfer this kerf mark to the face of one of the boards so you can see it while making the cuts. Make the 5 cuts through both boards while they remain clamped together in their offset position.
Remember, if a cut is slightly off to the left or right, it will be off on both boards by the same amount and, after step 7, each peg will still fit perfectly into the corresponding opening.
STEP 6
For the second set of 5 cuts, repeat steps 4 and 5 with the boards repositioned so that board B is offset to the left by one kerf.
STEP 7
When you have completed the second set of 5 cuts, separate the boards, transfer the "X" marks to the side of each board, and nibble the remaining material from the "X" sections.
There you have it, ready for the glue.
If, after using this method to make one joint, you need to adjust the width of the spacers used in step 4, remember that
- narrower spacers will produce narrower pegs and a looser joint
- wider spacers will produce wider pegs and a tighter joint
Here's the finished medicine cabinet.
