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Pro's Page
Author: Bill Hylton

 

Cutting Tenons with the Router

Router-cut tenons (and half-laps) have crisp shoulders and smooth cheeks

Most woodworkers know that the router is an excellent tool for cutting mortises, but how many realize it is great for cutting tenons as well.

A good tenon has straight, square shoulders and smooth cheeks. Smooth surfaces glue best, so you want smooth cheeks on your tenons. Gaps and misalignments at the shoulder not only degrade the jointís appearance, they weaken it. You want a clean and square intersection of the shoulder and the cheekóno ridges of waste, which could prevent the joint from closing completely. Also, the shoulders must be in the same plane all the way around the workpiece, so they seat tight against the mortiseís shoulders. 

Router-cut tenons match the criteria. And they are easy to make. Iíve got two approaches to routing tenonsóone for hand-held work, one for the router table. (I might add, parenthetically, that these are great approaches for cutting half-laps too.) For either, a simple-to-make jig, a sharp bit, and a good router are all you need.

Tenoning Platform

Cut tenons quickly and accurately with a tenoning platform, your DW610 router, and a mortising bit with a shank-mounted bearing

The tenoning platform is very simple to make and use. For plans click here. Lay it on top of the workpiece, clamp it and the work to the benchtop, and rout.

Use a bit that has a bearing mounted on the shank. For several reasons, I use a type of bit called a dado-and-planer, mortising, or bottom-cleaning bit.

  • It is designed to cut on the horizontal surface as well as the vertical. The tenonís shoulders thus are square to the cheeks, and both surfaces are smooth, perfect for a good glue bond.
  • It is short, typically with 1/2-in.-long cutting edges, so itís easy to make a 1/8 in. deep cut and still have the shank-mounted bearing riding on the platform edge.
  • It is available in large diameters (up to 1 1/2 in.), so you can cut a typical tenonís cheek in a single pass.
  • The bit can be run safely at the routerís full speed.

The jig itself is simple: two square flat platforms screwed to two straight fences. Because the bitís bearing rides along its edge during the cut, the larger platform must be dead square and must be square to the fences. The smaller platform is simply a secondary support for the router and an attachment point for the stop. The parts are small, so you can use scraps of hardwood for the fences and either plywood or MDF for the platforms.

Learn How To Make the Platform

Produce square shoulders all around the work piece by screwing a stop to the platform's auxiliary deck.

Hereís how to cut a tenon with the platform, step by step:

1. Place the stop. 

Lay out one shoulder of the desired tenon. Put the platform over the workpiece, align the platform edge on the shoulder line, and clamp the jig to the workpiece. Butt a scrap against the end of the workpiece , clamp it to the support platform, and drive a couple of screws through the platform into the stop.

2. Set up the router.

Set your rule on a scrap of the platform's deck to set the router's depth of cut.
Use a fixed-base router. If all you have is a plunge router, treat it like a fixed-base router. Set the cutting depth and lock it. If you do use the plunge feature, you are almost sure to accidentally cut into the platform itself, ruining both the jig and the workpiece.

Chuck a large diameter (1 to 1 1/2 in.) mortising or bottom-cleaning bit with a shank-mounted bearing in your router. A bit with a 1/2-in. shank is best.

Adjust the cutting depth. You can easily measure the distance the bit extends past the baseplate, but it may be more accurate to use a scrap of the platform material with your small rule. This is especially true if you used plywood for the platform. With the router unplugged, lay a scrap of the platform material on the baseplate next to the bit. Stand the ruler on the scrap and measure the amount you want to cut.

Make sure the bearing will contact the edge of the platform.

3. Clamp the platform on the work.

Use two clamps to secure the platform on the work, and both to the workbench.
Lay the jig over the work, with the stop tight against the end of the workpiece. The workpiece must be tight against the jigís fence. Clamp the jig and the work to the workbench, placing at least two clamps where they wonít interfere with the routerís movement.

4. Rout the first cheek.

Make the cut with the bits shank-mounted bearing riding along the platform's edge.

Set the router on the tenoning platform, with the bit clear of both the jig and the workpiece, but with the bearing against the platform edge. Switch on the router, and make the cut. The fence backs up the cut, so you donít get tearout. You will cut the fence, of course, and the tip of the stop as well; this is of little consequence. The bearing will prevent you from cutting into either the main or the support platform. Depending on the tenon length and the bit diameter, you may be able to cut the cheek in a single quick pass.

Switch off the router, but wait until the bit stops spinning before lifting the router. You donít want to inadvertently nick the edge of the platform.

5. Rout the second cheek.

Remove the clamps and the tenoning platform. Turn the workpiece over. Replace the platform, positioning it just as you did for the first cut. Reclamp it. Make another cut, just as you did the first.

6. Fit the tenon to the mortise.

With the cheeks cut, you can check how the tenon fits your mortise. It wonít fit it all the way in, because you havenít done the edges yet. But you will be able to determine if the tenon is the right thickness.

Too thin? Reduce the cutting depth slightly. (And start with a new workpiece.)

Too thick? Increase the cutting depth. (And cut your workpiece again.)

Just remember that you will be cutting both cheeks, so the impact of any cut-depth change will be doubled. If your tenon is 1/16 in. too thick, for example, increase the cut depth only 1/32 in.

7. Rout the edges.

To cut the edges, you stand the work on edge, then balance the platform on it while you apply the clamps. Because you seldom cut just one tenon, a good procedure is to cut the broad cheeks on all the tenons, then gang the pieces together and do the edges. You can gang as many pieces as will fit in the jig.

Once the work and jig are clamped, set the router in place, switch it on, and make the cut. Unclamp, remove the jig, turn the work over, reclamp, and rout the second edge.

Tenoning Sled for the Router Table

Learn How to Make the Tenoning Sled

With the right jig, tenoning on the router table is a snap.
If you have a router table, you can cut tenons even quicker. Given a choice, this is the way I do it. You can set up in two or three minutes, you donít have any layout to do, and you can cut a typical tenon in four quick passes.

You use the same sort of router bit (but you donít need the shank-mounted bearing). Guide the work with an easy-to-make sled thatís nothing more than a short, stocky T-square. The fence rides along the tabletop edge, so you get a straight, consistently placed shoulder cut. The fence holds the workpiece and backs up the cut, so you donít get tearout. A work stop clamped to the fence sets the tenon length.

Hereóstep-by-step, is how I set up and cut a tenon.

Measure from the edge of the cut in the fence to set the stop position for your tenon.
1. Set up the router table. Chuck the bitóthe same type used with the tenoning platformóin the router, and set the bit elevation. Use a small rule to measure the exposure of the cutting edge. Set the bit a little under, so you can creep up on the just-right setting through test cuts. (The just-right setting is determined, of course, by fitting a test tenon in a mortise.)

The work rides directly on the tabletop, so it is the reference surface for setting the bit extension.
2. Set up the sled. Use your small rule to set the stop next. Measure from the cut made by the bit into the fence. If the tenon is to be 1 inch long, for example, align the 1-inch mark on the rule over the edge of the cut. Slip the stop onto the fence, and bring it against the end of the rule. Tighten its clamp.

3. Cut a test tenon. Turn on the router and make a pass, cutting the first cheek and shoulder. Roll the workpiece over. Make a pass, cutting the second cheek and shoulder.

Check the fit of this tenon in your mortise. Raise or lower the bit, as necessary, to refine the fit. Cut another test tenon and fit it to the mortise. When you've got the settings right, cut the real work.

4. Cut the real tenons. Work and roll is the routine. With the workpiece in the tenoning sled, its end against the stop, make a pass, cutting the broad cheek. Pull the sled back, roll the workpiece onto its edge, and make another pass. Two more quarter-rolls and two more passes complete the tenon. If the tenonís length exceeds the diameter of the bit you are using, you simply need to make additional passes with the workpiece pulled away from the stop.

Obviously, "plain vanilla" tenons, which have the same width of shoulder all around, are the easiest to cut. An offset tenon takes two setups. This approach will produce excellent half-laps.

Begin your cut with the work tight against the fence, its' end butted to the stop.
Turn your work into the edge for the second cut. Keep it against both the fence and the stop.
Roll the work a quarter turn after each cut, completing the tenon in four passes.