4 Bits, 3 Joints, Too Easy! Vol. 2
You can easily create biscuit joints, splined corners, and finger joints, turning your router table into a joinery machine. All it takes are a few simple shop-made jigs, along with the step-by-step setups provided here. It's likely that you already own the bits required for these joints. If not, no problem, we've sourced them for you at the end of the story.
1. Order up biscuits
No biscuit joiner? No problem. You can create biscuit joints on your router table using a 5⁄32 " slot cutter [Source]. In the example shown in Photos A–G, I'm adding solid edging to a plywood shelf. Photos H–K show how to make end-grain cuts, such as when joining a rail to a table leg.
A. Locate the center of the bit by sliding a piece of scrap against the fence and the body of the slot cutter. Trace the end of the board onto the tape, marking both sides of the bit. Find and mark the center by dividing the line-to-line distance in two.
B. Set the depth of cut based on the size of the biscuit you'll be using (chart above). Then set the bit height to center the biscuit slot on the shelf. I use brass setup bars [Source] to make these adjustments quick and precise.
C. Clamp to the fence a cursor board with a line perpendicular to its edge. Align the cursor line with the bit centerline, positioning the board high enough so your material can just slip under it.
D. On the shelf, mark the center of each slot on the bottom (non-showing) face. Then add lines to the left and right, spaced half the Elongate Slot dimension. Align the left line with the cursor and plunge the workpiece onto the spinning bit.
E. Move the workpiece until the right line aligns with the cursor, and pull the board straight away from the bit. Repeat the process for each slot.
F. Remove the cursor board from the router table. Transfer the left and right layout lines on the shelf to the edging. Transfer the lines around to the front face of the edging.
G. Plunge the rear face of the edging onto the slot cutter, using the layout lines as start and stop points on the bit centerline, as you did with the shelf. Repeat for the remaining slots and assemble the workpieces with glue and biscuits.
JOIN YOUR LEGS TO AN APRON
H. To join a rail to a leg, calculate the distance from an edge of the rail to the center of the biscuit slot, and add half the Elongate Slot number. Clamp a guide to the fence this distance from the bit centerline.
I. With the outside face of the rail down on the router table, plunge the rail straight into and out of the slot cutter.
J. Rip a spacer equal in width to the Elongate Slot dimension and insert it between the rail and the guide, and plunge again.
K. Cut the biscuit slot in the leg using the same procedure shown for biscuiting a shelf/edging assembly [Photos F and G]. If you want an offset (reveal) between the leg and rail, raise the bit by the amount of the reveal before making this cut.
2. Add strength and style with splines
Build this jig from 1⁄4 " plywood and 3⁄4 " MDF. The stopblock and backer are not glued in place. Dimensions aren't critical, but make sure the angle at the bottom is 90° so your box won't move while cutting the slots.
Splines in a mitered box corner provide eye-catching detail and significantly strengthen the joint. To cut either straight or dovetailed splines, build the jig above, then cut the slots [Photos A–D].
A. Install a 1⁄4 " spiral bit in the router table, place the box in the jig, and set the height of the router bit (3⁄8 " here, for these 3⁄4 "-thick box sides). The 1⁄4 " plywood backer prevents chip-out on the exit side of the cut.
B. Center the bit in the slot in the jig's base, and lock the router-table fence against it.
C. Clamp the stopblock to the jig, measuring from the router bit to the block to locate the spline on the box.
D. Cut a slot in each corner. For symmetry, flip the box top for bottom and cut a second set. Relocate the stopblock for additional slots as needed. Cut splines to fit the slots, and glue them in. Trim the excess after the glue dries, and sand the splines flush.
Dovetail splines provide the illusion of dovetailed corners. The same jig works for cutting this joint [Photos E–H]. Prepare stock 1⁄16 " thicker than the bit diameter for splines and for testing setups.
NOW, DO A DOVETAIL
E. For dovetail splines, install a dovetail bit and set the height so the bottom edge of the cutter sits below the bottom corner of the box. Center the bit in the jig slot, as with the straight bit, add the backer and stopblock, and cut the slots.
F. To create matching splines, lower the dovetail bit, positioning the bottom of the cutter just below the table surface.
G. Position the fence so a small portion of the bit projects past the face. Make a test cut in a piece of scrap. Check the fit. If the dovetail is too large, move the fence back from the bit and recut the same edge. If the dovetail is too small, move the fence toward the bit and start on a fresh edge. Be conservative when moving the fence; because you cut each face, small changes have a large effect on the size of the dovetail.
H. When the fence is perfectly set, cut the final spline material. Rip the dovetail from the board, cut splines to length, apply glue, and tap them in. Trim and sand the splines flush after the glue dries.
3. Finger joints lend a helping hand
Glue and screw the base, brace, and upright together. The key is added later. The support gets repositioned, so don't glue it. Be sure the support has been machined square, or your project pieces won't fit correctly.
Ever wish you had a board stretcher? This technique joins boards end to end, without buying a specialized bit. It also works great on box corners. Build the jig shown below, and set it up as shown in Photos A–E. Note: The width of the project material should be an even increment of 1⁄8 " so the faces align when you assemble the finger joint.
A. Install a 1⁄8 " straight bit and set its height to 1⁄4 ". Position the fence 1 7⁄8 " from the center of the bit and make a 1⁄2 "-long cut into the jig.
B. Make a 1"-long hardwood key to fit the groove, and glue it in place.
C. Reposition the fence so the bit is 1⁄8 " from the key. Again, I like to use a setup bar.
D. Make a series of cuts in two scrap pieces by placing the edge of a test piece against the key. Make a cut, place the slot over the key, and repeat.
E. Slip the two pieces together to check the fit. If the fit is too tight, move the fence closer to the bit. If the fit is too loose, move the fence away from the bit. Make additional test cuts until you get a snug fit.
F. Increase the depth of cut of the router bit to 1⁄2 ". Butt the workpiece against the key in the jig. Steady a narrow workpiece, such as the one shown, by clamping the support against it. Cut the joint as you did with the test pieces, repositioning the support against the workpiece as you go.
G. Glue the joint, plane and sand the surfaces flush, and you've "stretched" your board.