How To: Make a Mortise & Tenon Joint on a Router Table : 10 Steps (with Pictures)

Using proper joinery can take your new furniture build from a cool 5 to a gorgeous 10. Adding a professional touch like mortise and tenon joints looks great but is also practical in making the furniture stand the test of time. I'm going to lay out step by step how to cut the joints on a common bench top router table.

It is a fairly simple process, but if at any point you get lost just check out the video at the top.

Supplies

Wood Pieces
3/8 Inch Straight Cut Router Bit
Router Table
Painters Tape
Pencil
Chisel or Sand Paper

Step 1: Laying Out Your Joint

Before getting to the router table lay out the pieces, make sure the edges are completely square and straight.

First we will start with marking out the mortise on the edge of the first board. For a typical 1X4 inch board (which is actually 3/4X3.5) the mortise will be 2 inch long, mark the edge at 3/4 inch and 2 3/4 inch from the end. This will be where the mortise is cut. Transfer the marks to the top surface of the board.

Next mark out the tenon on the surface of the second board. This will assist with getting a perfect cut and fit. On a 1X4 inch board mark the tenon at one inch deep with 3/4 shoulders on either side. These measurements will make a 2 inch wide tenon. It should look like the photo above once its all marked out.

Step 2: Setting the Table for the Mortise

First thing to do is set the depth and starting height for the mortise. The hole needs to be precisely center of the board edge. Align the fence so the center of the board lines up with the center of the bit. Using a scrap the same thickness, make a cut to check that the cut is exactly center of the board. Ensure your fence is square and lock it in.

To assist with aligning the cut put a piece of painters tape on the surface of the table and mark each side of the bit using a square off the fence. These marks will be your start and finish lines.

Finally set the bit height, rule of thumb is you never want to go deeper then the width of the bit. My tenon will be 1 inch deep total and I'm using a 3/8 inch bit so I will make 4 passes starting at and increasing a 1/4 inch at a time.

Step 3: Build a Stop Jig (Optional)

Build a stop jig using a scrap piece of wood. I chose to glue two pieces of scrap together using CA glue, and clamped it to the table. The advantage of a stop is easily repeatable cuts. Set the stop at the same distance from the bit as the second mortise mark is from the end of the board. For this board it is set at 2 3/4 inches from the leading edge of the bit.

Using a bench top router table means your piece will probably be longer than the table, meaning you can only use a stop on the left side of the bit. This means you will have to use the first line on the painters tape previously marked as a start point.

Step 4: Cut the Mortise

Lower the edge of the board on the second tape mark or the left edge of the bit. Slide the board against the fence until it hits the stop jig previously set. (or until the second line on the board meets the second line on the tape) Repeat the cut until you get the depth needed. Mine is 1 inch deep, four cuts will be needed per mortise at a 1/4 inch each.

Step 5: Table Set Up for the Tenon

Set the fence distance for the tenon to match the depth of the mortise. In my example the tenon length is 1 inch . Ensure the Fence is square and lock it in place. Check the cut with a scrap to make sure both the cut depth and distance from the fence is set correctly. It is very important not to move the fence after this. Similar to the mortise make several small cuts to ensure a tight fit.

Set the cut depth, the depth of the tenon will be the same as the mortise is wide. I am using a 3/8 inch bit so my tenon will be 3/8" in height. Go slow while raising the bit.

Step 6: Cut the Tenon

Use a scrap piece of wood when pushing the tenon through to keep it from kicking off square. Cut both sides of the piece, starting with the cut against the fence first. Similar to the mortise make several passes adjusting slightly higher on each pass. Dry test fit the corner of the tenon as you go removing a tiny bit at a time, this will ensure a tight fit. Raise the bit by half what you want to remove. The tenon needs to be cut equally on both sides. Therefore when the bit gets raised it will remove twice as much material as it is raised.

Step 7: Cut the Tenon Shoulders

Complete the tenon by standing the piece on end and cutting the top and bottom shoulders. Do not adjust the fence depth from the first tenon cut. Use a backer block when pushing the piece through to prevent kickback. Ensure the fence is completely closed for this part to keep the piece from falling into the gap. The tenon needs to be 2 inch across to match the mortise. In my example I cut 3/4 inch shoulders on each side because my board is 3.5 inches wide, leaving a 2 inch tenon.

Step 8: Final Adjustment

If you used a straight cut bit, the mortise hole will be round and the tenon will be square. Round or remove the corners of the tenon. You can use a sander, file, or as I prefer a chisel will easily do. Now that they are both the same shape push them together and you should have a clean tight joint.