If you’ve never cut mortises with a plunge router to create loose tenon joinery or your previous attempts to mortise with a plunge router were met with less than stellar results, read on, you’re in for a surprise. I’d cut the stock to length and place them in freezer bags to keep them from absorbing atmospheric moisture and swelling until I needed them. A stopped (blind) mortise-and-tenon joint is one in which the tenon is hidden fully in the mortise (see Figure 2). This type of tenon is often used on table and chair legs or anywhere else that you don’t want to see the joint. Use a router + edge guide to cut the tenon, referencing off of the end of the board.
For cutting tenons, a table saw with a dado blade and tenoning jig can cut the tenons quickly and accurately each time. Turn the board on it’s edge and cut your shoulder the same way as you cut the thickness slowly working your way to the fence. It just seems that there are Japanese saws more suited to the types of sawing operations that a woodworker making furniture projects will be doing.
Leaving the router stops in the exact same position as they were for cutting the mortises in the leg, I position the center line of the apron with the center line of jig, clamp in position, use the center finding pin to locate the center line of the mortise and route the mortise. To make the jig, cut a piece of plywood or MDF to 280mmX380mm and cut a notch off one of the corners to make clearance for the router cutter.
Taking an aggressive cut can cause bit deflection resulting in a wider than expected mortise, rough mortise walls and a mortise with less than perfectly straight side walls. Next you can use your recently cut tenon as a guide for the width of your mortise and you do this by resting it across the timber that will have the mortise and drawing lines along the two edges of the tenon. I followed the same procedure to cut the shoulders and cheeks on the narrow faces.
Either hog out the main area with the bench saw and finish with a chisel or use a router. Use an adjustable square or a table saw blade-height gauge to set the blade’s height. Like the dovetail joint, a mortise and tenon can be carved by hand, but that requires a certain skill level and aptitude for using a wide variety of hand tools. The front clamping face on the jig body also tilts out making it possible to easily cut angled mortises. In the western saw world, the 210 mm ryoba would take on the role of the rip and crosscut tenon saws, and the dovetail saw.
Raise your saw blade until the tips of the teeth touch the bottom cheek layout line you drew in Step 3. Slide the rip fence over so the outside face of the blade intersects the shoulder layout line you drew in Step 2. Lock the fence. Once the setup is dialed in, the workpieces can be run over the dado set as a group to cut all of the haunches at once. That keeps both shoulder cuts lined up and when the cut gets going I lean the saw back, and stop when I reach the line for to end cuts on the tenon. However, he explains how blade flex can leave a slightly angled tenon face, especially with larger tenons.
The Tenons (as already stated) are generally one-third the thickness of the timber, thus leaving the same amount of substance at each side of the tenon as the tenon itself is composed of. The mortise gauge is set to the required distance and used as in the case of the marking gauge ( Fig. I’ve cut thousands of tenons and use a good router table with a large straight bit with a fence.
With a bandsaw or hand saw, cut down the middle of your lines and stop before you reach the shoulder. A router with an upspiral bit is the preferred power tool for cutting a mortise, and an edge guide attached to the router base ensures a straight cut. Another chapter covers cutting tenon shoulders on the table saw, with the usual level of detail on accurate set-up. Using a table saw and tenoning jig is the best way to form the tenon portion of this joint.
Solid carbide spiral up cut router bits are designed and manufactured for mortising among other tasks. The ones I use have a V” tip which allows for this type of plunging while others have the tip of the bit cut on an angle to facilitate plunging, either one will work. I then place a 45 chamfering bit in the router and chamfer the clamp holes on both the front and back sides of the side panel resulting in a clean edged hole that won’t splinter when relocating the clamps from one hole to another. Install them so that they only go half-way into the dado so there is room for the table to expand.
Cut the piece and place the router horizontally and then route the tenon on the stretchers with your router. When I first started mortising with a router I learned one very important lesson rather quickly…accuracy is everything. I will then cut the shoulders on the tablesaw using an offset block clamped to the fence so that the cutoff has somewhere to go.
Some woodworkers are under the impression that you can plunge a router bit (straight or spiral) into a mortise and hog out 1/4″ of material or more at a time. He explains why he still prefers the table saw, especially for shoulder cuts, but some might prefer the safety of a bandsaw or might have a table saw that is not up to the finest of work. He shows you how to cut kerfs into the tenon, hand chisel angled end walls on the mortise and make wedges of the correct angle with contrasting wood. Getting a good start is the key to making a good cut as the saw will want to follow the kerf.
Undercutting the shoulder is bad practice, so avoid it. The paring stage is where you reap the benefit of a clean, deep knife line cut during the marking out stage because the chisel will seat firmly in the knife line. 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. Then, with the blade spinning, slide the workpiece along the mitre gauge so that the wood approaches the blade from the side, like a 90° cove cut. Cut 3 — Remove the chisel and position it another 3/16″ towards you for Cut 3, which will go deeper yet.
If you have more than a couple of tenons to make, you quickly cross the line where a different set up would take less time overall. Depending on the tenon length and the bit diameter, you may be able to cut the cheek in a single quick pass. Have no doubt though that people have been doing this bump cut since table saw`s have been around, and in terms of no nos it isn`t even on the major radar screens. When sawing, take time to check that the saw is cutting straight down and that it is on the waste wood side of the tenon.