Q:
I’ve built a few boxes with mitered splines on the tablesaw, and now I want to try my hand at dovetail splines. I know I can use a jig to cut the slots in my box at the router table, but how do I make the splines?
John Mihalick, Pensacola, FL
A:
The secret to getting the splines to fit is to use the same dovetail bit you used to cut the slots.
Start by cutting the slots in the side of the box with a dovetail bit and a jig. Once all the slots have been cut, raise the dovetail bit about 1/16-in. The extra height makes the splines, also known as dovetail keys, slightly taller than the slot, and easier to trim to fit. Then bury the bit about halfway into a zero-clearance fence on your router table. Make the keys from a piece of stock that’s slightly thicker than the widest part of the dovetail slot, and at least several inches too wide. The extra thickness lets you adjust the fit of the keys, and the extra width makes it easier to grip and to register the workpiece against the fence.
Make one pass with the face of the workpiece against the fence to cut half of the key. Then flip the workpiece and run it back through the bit to cut the other half. Testfit the piece in one of the slots. If it’s too tight, nudge the fence to take a slightly deeper cut from one side. It doesn’t matter if the key is not centered on the board because you’re going to cut it off anyway. Once you’re close, use a block plane to take a swipe or two from the bottom, fatter part of the key to make it fit a little looser.
Cut the key stock from the board with a bandsaw, crosscut the keys to rough length, glue them in the slot, and then trim the keys flush with a block plane.
One bit, two cuts. Ensure a perfect fit by using the same bit to cut the keys and the slots.
Use a sled for the slots. A simple jig, registered against the fence, holds the box at 45° and makes it easy to cut the dovetail slots.
Better keys in bigger pieces.Rout the key on the bottom of a larger piece to stay safe and get a clean cut. Raise the bit a little from its earlier position. Also, bury it in a sacrificial fence if possible.
Adjust the fit. If the key is too thick, move the fence and recut one side.When it fits, rip away the key stock, and crosscut keys as needed.
Fine Woodworking Recommended Products
Veritas Standard Wheel Marking Gauge
Leigh Super 18 Jig
Pfiel Chip Carving Knife
Comments
An alternative, and easier, method is to build a table saw fence and use a thin blade set at the angle of your dovetails, e.g., 14°. Use a stop block to cut to the width of your dovetail slots and a work piece about 3/4" thick and about 2" wide. Make a first cut, then rotate the piece and cut again for the first spline, again and again. Adjust stop block as necessary. This is great if you cut many dovetail splines.
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