Designing the Joint

The main goal i n designing a mortisc-and-tenon is to maximize the glue area, especially the long-grain-to-long-grain glue surface. Choose the joint and its proportions according to the job it must do.

Here are rules of thumb for establishing the width and length of your tenons. The size of the mortise follows, obviously, from the size of the tenon. (It's much easier to match the tenon to the mortise, so when making the joint, you nearly always make the mortise first.)

The bigger the tenon, the stronger it will be. but at the possible expense of the piece with the mortise in it. You don't want the mortise walls to be too thin.

You have to keep in mind what will be required of the pieces involved. For example, aprons mortised into table legs will be under tension-compression stress, so the tenons need as much height and length as you can provide. While the tenons won't get much shear or torque stress, the legs will be heavily leveraged, so you don't want to weaken them. The upshot: Make the tenons fairly thin.

In frame-and-panel work, where the pieces are likely to be the same thickness and will be experiencing similar stresses, your tenon should be somewhere between one-third and one-half the total stock thickness. In door consrmction, where a panel is set in a groove inside the frame, it's common to use the haunchcd tenon and to for rcs use


STILl ble leg and apron frame for panel table leg amd narrow apron below a drawlr make the tenon thickness match the width of the groove. The haunch on the tenon fits in the groove, and it enhances the joint's resistance to twisting—an imponant consideration in door consmtction.

When the tenon piece is narrow, there's sometimes a temptation to run the tenon across the grain. An example is the apron above or below a drawer in an occasional table. The tenon has long grain, but the mortise in the table leg will be all end grain: the resuk is a weak gluing situation. It's better to make two short, narrow-tenons.

Occasionally, you'll need to make an angled monisc-and-tenon joint. A good example is a chair, where the scat tapers from front to back; the side rails meet the legs at an angle. The mortise can be cut square to the leg's surface and the tenon on an angle. But sometimes the resulting tenon is weakened because it doesn't have enough long grain extending from its end all the way into the rail. Better choices would be to cut the mortise on an angle and the tenon straight, or to use loose tenons. Loose tenons arc a particularly good choice for router-cut joiner)' because both the mortises can be easily referenced perpendicular to the mating surfaces.

cinch down its setscrews. Now you are ready to rout.

Plunge-cut the ends of the mortise first. Doing this ensures that the ends of the mortise will be vertical. Then rout out the waste between the ends in a scries of passes. Plunge a little deeper for each pass.

When you cut, be sure you feed the router in the right direction, the one that uses the force of the bit rotation to pull the guide against the work. This will ensure that the mortise is straight.

You can position the router even more positively using two edge guides. With one against each side of the work, the router can't drift. Not every commercial edge-guide system will allow you to do this. The router may accommodate one, but not two. You can make your own, of course, as shown in the plan for the double edge guide in the chapter "Sliding Dovetail Joint."

The double edge-guide setup is particularly useful for routing mortises that have a width greater than the bit diameter. The guides can't both be smack against the sides of the workpiece. of course. To set them, position the router on the work, with the bit plunged to the work surface

Depending upon the setup you use, you may only need to transfer the extremities of the mortises from one fully la id-out part to all the others. Stack the parts, ends flush, and use a square to do this.

and aligned over the laid-out mortise. With the bit aligned at one side, set the far guide. Then shift the router to the opposite side of the mortise and set the second guide.

.As you make the cut. remember to feed the router so the bit rotation pulls the far guide against the workpiecc. You still plunge both ends of the mortise to full depth; you just have to plunge at least twice at each end to accomplish this. Then waste the intervening stock in a series of incrementally deeper passes.

Providing adequate bearing surface. This is one of the perpetual bugbears of router woodworking. It's like balancing a # 10 soup can atop a board fence, when the soup inside is being stirred 22.000 times a minute.

The typical plunge router is a

When the mortise width exceeds the bit diameter, use the double edge-guide baseplate. To set the guides, align the hit over the laid-out mortise. With it aligned at one side, set the far guide, as shown. Then shift the router to the opposite side of the mortise and set the second guide.

top-heavy 12-pounderwith a base 7 inches in diameter. If it's centered on a workpiecc Wi inches wide, you won't have support directly under the plunge rods. Should there be the slightest drag on one rod or the other as you plunge, the router's going to tip.

You need adequate support for the machine. How do you get it?

One good way is to clamp several workpicccs together. For example. if you are mortising table legs, you can clamp three legs side by side in a bench vise. (Any more than three would be cumbersome to (lush up and, later, to shift around.) Collectively, they'll provide a flat surface for the router base. If you mortise the middle leg. you'll have equal support for the router's entire base.

A common routine is to plunge the bit and then push or pull the machine to actually rout the waste. Then you return the machine to its original position and plunge a little deeper. The risk in this is that the bit will grab on the return, gouging die mortise wall. To avoid this Tisk, you should make the cutting pass, then retract the bit clear of the work before drawing the router back and replunging the bit for another pass.

After mortising this first leg, simply reposition the legs, with a new one in the middle position. Keep shuffling the legs until all have been mortised.

The approach minimizes setup time and provides excellent suppon for the operation. It doesn't work as well, however, when you're monis-ing >Vinch stock, since three such members don't add up to enough support. You might better sandwich such pieces between straight, flat lengths of beefier stock.

Fred's had good luck holding work in a vise. He blocks it up on

When mortising table legs, you can support the router by clamping three of them in a bench vise. Your first setup should have the leg with the fully laid-out mortise in the middle. Set the router's edge guide to reference one of the outside legs.

This jig holds a workpiecc between two wide fences that provide good support for the router as well as a reference surface for the edge guide. Stops can be added to eliminate the need to lay out the workpieces. And the jig can be adjusted to accommodate work varying in thickness and height, too. Altogether, it's most excellent!

the vise rods until the top is flush with the jaws, then routs. If you need a fence to guide the router, you can use double-sided tape to stick a tall wooden facing to one of the jaws. With it projecting above the work, it can serve as your fence.

Minimizing the workpiccc handling is most imponant when you have a tall stack of pans to mortise—stiles for slx or eight cabinet doors or legs for a set of chairs. I'm willing to shuffle three-leg bundles in and out of a bench vise when four legs is the total. If the extent of the job is beyond that. I want a jig into which I can quickly clamp the workpieces.

The Excellent Mortising Platform

Here it is, and it is most excellent. Pivotal to its ease of use is the pair of DeStaCo toggle clamps (model TC-605 push-pull type). Once the movable fence is adjusted for the thickness of stock being mortised, securing a workpiecc is a matter of slipping it between the fences and pushing the two toggle clamps simultaneously to clamp it. When the mortise has been routed, pull the two toggles simultaneously to release the workpiece. Lift it out and drop another in its place. The movable fence is attached to the toggle clamps, so it won't get bumped out of alignment or tumble ofT the workbench. No loose clamps either. And no extra blocking.

The platform can be clamped or dogged to a workbench or the router bench. I orient the platform so the fixed fence is at the workbench edge, so 1 can have the router's edge guide referencing my side of the jig. It's easy to reach across to the toggle clamps.

This jig holds a workpiecc between two wide fences that provide good support for the router as well as a reference surface for the edge guide. Stops can be added to eliminate the need to lay out the workpieces. And the jig can be adjusted to accommodate work varying in thickness and height, too. Altogether, it's most excellent!




root t-3l0t for ' bolt ue.a0 with keyhole nt-

fc"«2var«iatt bolt









Piece Number Thickness Width Length Material





Birch plywood

Clamp base-





Birch plywood

Fixed fence top





Birch plywood

Fixed fence sides



2 W


Birch plywood

Fixed fence blocks



2 Yi"


Birch plywood

Movable fence top





Birch plywood

Movable fence sides





Birch plywood

Movable fence blocks





2 DeStaCo TC-605 push-pull toggle clamps. Available from Reid Tool Supply Co., 2265 Black Creek Road, Muskegon, Ml 49444 (800-253-0421).

3 pes. #6 x 1 Ya" drywall screws

To make the mortising platform:

1. Cut the base and the clamping base to size, and glue the two together.

2. Make the fences next. Start by cutting the fence parts to size. Glue the doubled fence blocks together; you need three such blocks Tor each fence. Cut the dadoes in the fence sides, as shown in Excellent Mortising Platform. Rabbet the sides, top, and end blocks. Assemble the fenccs.

3. Using a Mt-inch keyhole bit, rout two slots in the movable fence for the heads of the carriage bolts that attach the fence to the toggle clamps. You may need to widen the slots to accommodate the bolt heads; rout the slots to fit.

4. Glue the fixed fence to the base. Align it flush with the edge opposite the clamp base. Drive drywall screws through the base into the fence.

5. Mount the toggle clamps on the base. To position them, turn the carriage bolts into the toggle clamp plungers as for as they will go. Roughly position the clamps, then fit the mov able fence over the bolt heads. Align the fence; adjust the clamps so they are perpendicular to the fence and equidistant from the edge of the base. Fasten them in place with screws.

To use the mortising platform, you must first set the fence to secure the workpiecc you are routing.

The gap between the fences is adjusted by turning the carriage bolts in and out of the toggle clamp plungers. The plunger is tapped 1 inch deep, so to vary the gap more than about Vi inch, you need to switch bolts.

To set the fence, install bolts of the proper length for the coarse setting. When they arc seated in the plungers, you should be able to push and lock the clamps and have the fence against (or almost against) the workpiecc. To tighten the fence so it will in (act secure the workpiecc, push and lock the clamps. Turn the bolts as right as you can, seating the fence against the workpiecc. Then pull the clamps, and give the bolts an additional fraction of a turn— about one-eighth tum.

Test the setting by pushing the clamps and locking the fence. Ifyou can move the workpiecc. you need to tighten the setting further. Ifyou can't push the clamps completely closed, you need to loosen the setting.

Lay out the mortise on the workpiecc. Chuck the bit you are using in the router, and set the plunge depth. Set the router on the work, and plunge the bit, aligning it over the mortise layout. Set the edge guide, and cinch down its setscrews. Now you are ready to rout.

The guide is set for all similar mortises. Ifyou are doing 50 mortises, all in the same place on each work-picce, you don't have to mark each piece. Instead, mark the fixed fence. Make an alignment mark on the fence top to use in positioning the work-piece. Then mark the ends of the mortises on the fence top. Use a different color for this, if that'll help you keep the different marks straight in your mind. The router's edge guide will establish the mortise position laterally, and you can eyeball the beginnings and ends of the cuts from the marks on the fence. (When you're done, erase—or sand, if necessary— the marks from the fence.)

Better yet, ifyou have a rectilinear baseplate on your plunge router, attach stops to the fixed fence. Use a piece of double-sided tape to stick a thin stop block to the inner wall of the fence; butt the workpiecc against this stop when setting it in place. Trap your already-mortised work-piece in the jig, plunge the router bit, and set it—with the router switched off, of course—in the mortise. Set a stop against the router base and stick it to the fence top. Move the router to the other end of the mortise, and set a second stop. As long as you don't smack the router against these stops, you can set them with that carpet tape. (You know. Pretend you're parking your new car. and you don't want to ding the shiny chrome.)

The usual routing technique, as noted before, is to plunge-cut the ends of the mortise and then rout out the waste between these holes with a series of incrementally deeper passes. Remember to feed the router in the direction that will pull the guide against the work.

Trough-Style Mortising Fixture

A useful, practical, and easy-to-make mortising fixture is this miter-boxlike construction that clamps in a bench vise. The router is supported by the sides of the fixture, and its edge guide references the outer face of one side. (You could use two guides with this fixture, to trap the router in position.) Stops screwed to the side control the length of the mortise by limiting the travel of the edge guide.

To use the fixture, you clamp it in a vise. Remember to make a work-piece alignment mark on the fixture. Position the workpiece in the trough, clamping it to the main side. (You

Attach temporary shims and a positioning slop to the fixed fence using carpet tape. The shim lifts the work so it is flush with the top of the jig. Set lite work in placc, and flip the toggles to wedge the second fence against it. may need to use a scrap block under the workpiece to bring it up to the top edges of the trough.) As with other setups, you position the bit over the laid-out mortise and set the edge guide to establish the lateral alignment. If you want to use stops, just drive a couple of screws through each into the side.

With a simple modification, this fixture is ideal for routing angled mortises, such as those you'd want in chair legs. All you have to do is bevel one of the sides, reducing its height in the process. When the router is set on the fixture, the bit will be cocked off-plumb.

Was this article helpful?

0 0
Woodworking Tools and Installation Tips

Woodworking Tools and Installation Tips

There are a lot of things that either needs to be repaired, or put together when youre a homeowner. If youre a new homeowner, and have just gotten out of apartment style living, you might want to take this list with you to the hardware store. From remolding jobs to putting together furniture you can use these 5 power tools to get your stuff together. Dont forget too that youll need a few extra tools for other jobs around the house.

Get My Free Ebook

Post a comment