The Dovetail Plug Template Homemade Machines & Jigs

Back in September of last year, I made some stackable parts trays and reinforced the butt joined corners with a special kind of spline. At that time, I made a video of how I made the dovetail plugs:

In the video, I said I would give details on the template at a later date. Since I’ve had quite a few requests for the template, I put together this article to post it for download and give some instructions on how to make and use it.

Here’s the finished result:

Attractive and functional, the plugs (or splines) can be the same species of wood, or a wood of a contrasting colour. You can even cut them from another material, like plastic and glue them in with epoxy.

I took some pictures from the video to go over the basic procedure for cutting the plugs and pockets. Here I’ve clamped the template to the box I want to reinforce and I’m using the router equipped with a 5/8″ collar and a 1/2″ x 14° dovetail bit:

It cuts the pocket to the correct size and shape.

The plug cutting part of the jig is used next to make the piece that will fit in the pocket. Here I’m cutting the plug free of the larger piece:

And it’s a perfect fit. The dovetail spline just needs glue and to be tapped in firmly to hold – it requires no clamping.

Shortly after finishing the video above, I put together a template for the jig. At the time, I was most of the way through doing it (it actually takes longer to develop a template like this than most people realize), when I got pulled away from it and didn’t get it finished. Fast forward to the present, and I have forgotten which of the several templates I have saved on my computer is the correct one! So, I picked the one that looked the most promising and printed it:

The next step was to actually test it, and to do that I pasted it to a piece of 1/4″ thick plywood. When I made this template, I had the somewhat silly idea to make it with two thicknesses – 1/4″ and 1/8″. I realize now that it was a waste of time, and this new template is only for plugs that are 1/4″ thick.

Rough cutting it on the band saw:

Sanding it to the lines on my spindle sander.

Next step is to test it, and here it’s clamped on to cut out the pocket:

Next, I cut the plug. It’s very important that the depth of the cut be set to exactly 1/4″. If it’s more or less, the plug will not fit properly in the pocket. While cutting the plug, it’s crucial that the collar on the router be kept up tight to the sides of the cut out on the jig. If it moves inwards, it will ruin the plug.

As expected, the fit was not perfect on the first try. The fix is to sand the pocket cutout on the jig a bit bigger, if the plug is too tight, as this one is:

After recutting the pocket, I’ve gotten a bit closer. It’s still not good enough, so it’s back to the sander for more adjustment. Taking the time now to make the jig exactly right pays off when using it on future projects.

The third time is good, and the fit is acceptable. The dovetail plug should have just a small gap at the nose before it’s tapped in tightly:

When sanded smooth, it’s nearly a perfect fit and hard to see where it is.

With the template perfected, I traced around it onto a piece of paper:

Then scanned that into my computer. I then added some text instructions to it and the finished template is here:

Dovetail Plug Template

Clicking the link above will open the template in your browser. Right click the image and select “Save image as…” to save it to a handy place on your computer (desktop, for example).

To print the template, open it with you favourite printing utility and set the size to “full size” or “no scaling”. Here is the print set up in Irfanview (a free picture viewer):

The overall size is not overly critical. When printed, the ‘nose’ of the pocket cutting portion should be big enough for the 5/8″ collar to fit into properly. Making the template bigger will produce a bigger pocket / plug, but making it smaller will not work, since the 5/8″ collar will not go all the way to the tip of the pocket.
Again, It’s important that you set the depth of cut on the router to 1/4″, as the template is sized for that thickness.
After you have made your jig, test it (as I did above) to make sure the plug is a good fit in the pocket. Adjust the jig as needed to get the best fit.