The butt joint embodies simplicity, but can fall flat on strength, especially when end grain or thin stock are involved.
2 boards with dark splines

The butt joint embodies simplicity, but can fall flat on strength, especially when end grain or thin stock are involved. Splines and bowtie keys (shown here) reinforce and add elegance to the joint while assisting with alignment during assembly. Here's how to add both elements.

Tablesawn splines keep clean lines

To add this detail to your project, first mount a tall extension to your tablesaw's miter gauge. Then, determine the position and length of the splines. Use your tablesaw's fence to locate the first spline, and then raise the blade to half of the spline's length. Make the mating cuts in all pieces before moving the fence or adjusting the blade height [Photos A, B].

A Yellow clamp making second cut
Clamp the workpiece to a tallmiter-gauge extension withone edge against thetablesaw's fence. Make the cut.
B Second cut on board
Without moving the tablesaw'sfence, hold the adjoining pieceto the miter-gauge extension.Make the matching cuts.

Cut spline stock to fit the kerfs [Photo C]. To help with alignment during the final assembly of the joint, glue the splines into only one workpiece at a time and let dry before gluing the mating piece in place.

C Board with 2 long splines
Match the spline stock width tothe thickness of the frame for aflush fit, or 1/8" wider so theystand proud.

Bowtie keys add a touch of class

First, mount a dovetail bit in your router table. (The bit diameter and cutter angle don't matter.) With a tall extension fastened to your router table's miter gauge, adjust the fence to center the bit on your workpiece and rout the dovetail [Photo D]. Repeat for the other half of the joint on the adjoining piece [Photo E].

D Miter-gauge extension
Clamp the first workpiece to therouter table's miter-gaugeextension with an edge againstthe fence before cutting through the workpiece.
E Routing without fence
Without moving the router table'sfence, clamp or hold the secondpiece to the miter-gauge extensionand against the fence. Make thematching cut.

Make the perfect-fitting bowtie

Now, plane a blank of contrasting wood so its thickness matches the width of the dovetail bit. Crosscut the blank to a length twice the depth of the dovetail slot. Without changing the bit height, move the router table fence to cover half of the bit's diameter. Make repeated passes along the length of the bowtie-key blank, flipping the piece end-for-end and over until the bowtie is fully shaped [Photo F].

Pushblock at an angle
Use a pair of pushblocks to keep the bowtie key stock tight to thefence. Sneak up on the final widthof the key by making additionalpasses as necessary.

Check the bowtie-key blank's fit in the frame's dovetailed kerf. If the blank is still too wide, nudge the router-table fence back to expose more of the bit and make additional passes until it fits. Rip a key from the blank and glue it in place [Photo G].

Butterfly spline
On raised bowtie keys (andsplines) carefully add a bevelto the proud edges using a sharpchisel after the frame has been assembled.