From tabletops to drawer bottoms, edge-to-edge joinery is found throughout furniture making, so it is worthwhile to explore the issues involved in preparing, cutting, and gluing up these joints.

For most of the steps there are a variety of good approaches, particularly based on the size of the joint and the available tools. The outright errors usually come from injudicious wood selection or inattention to the key tolerances in the joint.

As we woodworkers can’t help but notice, edge joints that have opened up can be found everywhere. But why? After all, if the bonded glue line is really as strong as the wood itself, it should not have any more propensity to split than the adjacent wood.

One of the large drawer fronts at the factory-made red oak desk where I am typing has a small edge joint failure. A cross grain conflict with the particleboard sides is stressing the solid wood front but why is the split at the glue line?

Whether due to luck or skill, pieces that I made 25 years ago have fully intact edge joints but, again, why?

So let’s think about this fundamental joint in a short series of posts.

Keep in mind that a little split here and there usually does not affect the function of the piece. My workbench, which I’ve used for more than 30 years, has several splits in its top that don’t bother me one bit. In fact, they seem to function as built-in stress relievers that probably help maintain the remarkably consistent flatness of the top throughout the seasons.

Wood selection

It is surprising how often we see mismatched glueups in otherwise fine work. A door panel with flatsawn cathedral figure running out at a glued edge adjacent to straight rift figure looks like it came from a factory, not the shop of a craftsman. Below is a factory-made door panel that is devoid of human finesse.

It is best to match the figure at adjacent edges and generally avoid edge runout of flatsawn figure. Join rift to rift and quartered to quartered. Cathedral figure boards are best joined where there is rift figure beyond the width of the arches – ideally where the figure lines are nearly straight. Where this is not possible, try to have the figure lines flow into each other across the glue line. In this way, attention is not called to the joint line and the completed panel looks harmonious.

Below, even in this book-matched panel where the halves are necessarily mirror images of each other, the boards blend together and the joint line (indicated by the pencil) is barely detectable.

Joining a quartered-grain edge with a flatsawn-grain edge, for example, not only looks poor but the thickness of each board at the glue line will undergo different seasonal change because of the different orientation of the growth rings. This can produce a tiny but disconcerting step on the surface at the joint line. The joint is stressing itself from this conflicting movement.

In summary, join similar edges to produce visual and structural harmony.

Next: Should you alternate the growth ring orientation of flatsawn boards in a glued up panel? Also, we’ll consider the camber question.

Good job! You developed a compelling design, skillfully employed sound construction techniques, and lavished care on your baby – I mean woodworking project. And of course, you applied a finish that made her look fabulous when she – uh, it – left the shop.

Well, it’s not over because it’s a jungle out there. Consider especially that pretty finish in which you sent your furniture/accessory oeuvre out into the world.

Think about the likely use and possible abuse of the piece. Sure, a wall cabinet for art objects will not suffer as will a dining table, but will that hall table display family photos or have keys and wet umbrellas tossed onto it? Will later owners of the piece value it as much as the original owner?

A key issue is that the durability and reparability of a wood finish are generally inversely related. For example, oil-varnish mix is not very durable but is easy to repair, while a tough polyurethane film finish is more difficult to repair.

I think in many cases it comes down to which is more tolerable: dented, scarred wood or a dented, scarred thick film finish. Ultimately, water, abrasion, and ultraviolet light can break down any finish, resulting in something like the table top below. When dirt and grime get into the grain of the wood, restoration gets even more difficult.

One approach, which is gaining appeal with me in some cases, is to take it easy and apply a few coats of oil-varnish mix. I like Rockler’s Sam Maloof poly-oil because of its high solids content and amber color that is not too dark like some oil or varnish products such as Waterlox. It leaves a low-key sheen that allows one to “take pleasure in the wood surface,” as the late, great Sam said.

The car key abrasions probably will look better – and maybe even add character – in a wood surface finished with oil-varnish mix that can be easily touched up by anyone, than in the layers of a heavy film finish that will probably never be repaired by anyone.

There are always trade-offs. The point is to think it through the long term when choosing a finish.

Here is a palpable way to look at power tool safety.

This occurred to me as I was holding in my hand the DeWalt DWP611 compact router. It is so easy to wield this little machine with one hand – it’s easier to grip than a youth-size football – that I sensed a bit of over-confidence sneaking in as I was preparing to put it to the wood.

This little beast, however, has a tail that plugs into an electrical outlet, so it can generate 1.25 HP. Question: are you more powerful than a horse?

Moving over to the table saw, here’s another question. The tip speed of a 10″ blade at 3450 RPM is 103 MPH. Think about kickback. Are you faster than that?

There is no way the woodworker is strong or fast enough to beat an out-of-control power tool. Therefore, the operation to be performed must be fully controlled and fully predictable. There is no room for doubt or hoping. You must know what is going to happen before it happens.

It is difficult to over-emphasize: we ultimately must control our power tools with our brains. Knowledge, proper setup, patience, and alertness are absolute requirements.

Without them, we’re just not good enough.

In building furniture, woodworkers wonder if the joints will be strong enough to withstand the many years of rigors to which they will be subjected.

As we parse the elements of joint design, figuring if a tenon is long enough, dovetails deep enough, and so forth, we rely upon hundreds of years of cumulative experience in furniture design and observation of how pieces have fared over the years. We also can benefit from some of the joint testing done by the magazines, data from the Forest Products Laboratory, and of course, a healthy dose of intuition.

However, there is a shortcoming in viewing joint design too narrowly.

Assuming competent joinery skills, answers to structural strength questions are more likely to come from broadening one’s view beyond the joint under consideration and looking at the whole structure of the piece. This will make the requirements for a particular joint more evident.

Here we must ask:

• What is going on in the overall design of the piece that will transfer stress to that joint, and on the other hand, help it to resist stress?
• How will normal use, and perhaps abuse, stress the joint?

For example, this table has fairly narrow legs that allow only shallow mortise and tenon joints. Force applied to the lower part of a leg produces considerable moment at the joints. Racking in the horizontal plane could also be a problem.

However, looking beyond the leg joints shows they have plenty of help. The two cross stretchers are joined to the aprons with sliding dovetails, and there is a corner block behind each pair of leg joints.

As another example, in a bookcase, the joints attaching the horizontal to the vertical members are subject to huge racking forces. Yet, a thin plywood back fastened to the back changes everything.

The point is that when designing furniture and wondering if a particular joint will be strong enough, let the big picture inform your engineering decisions.

There are lots of recommendations available for warming up to saw joinery but here I will concentrate on two aspects:

• The progression of the warm-up
• Core muscle activation

The progression

Any good warm-up should include aspects of the main event. To prepare for sawing dovetails, for example, saw to a series of lines that mimic dovetails. As you begin, recall and concentrate on basic technique and mechanics without being primarily concerned about hitting the lines perfectly. You’re like a baseball player before a game, at first taking easy batting practice pitches while just trying to execute sound form and make good contact. Address any neglect of the fundamentals.

Then bear down and try to make a couple of dead-on cuts. Observe the results, sharpen your mind, and clean up your technique accordingly. Find your familiar physical and mental groove.

Make sure there are no deficiencies in your tools and setup, including the lighting. The warm-up also gives you a chance to sense the density and grain of the particular wood at hand and make appropriate adjustments in technique.

For work that you do frequently, the warm-up should be very brief. Even if you’re a bit rusty, it should only take a few minutes, provided your skills are fundamentally sound.

An exercise to engage the core

Only when the core – glutes, hips, upper back – is strong, engaged, and balanced, can the peripheral parts – shoulder, arm, and hands – move with accuracy and precision.

Try this exercise. Make a small, shallow pile of sawdust on your benchtop or scrap of wood. Attempt to create “kerfs” in the pile by pushing the dust with the teeth of your saw without the teeth making contact with the benchtop.

It can only be done with your core muscles engaged, along with a balanced stance.

When sawing joinery with a backsaw, the saw should not be helping to support you. If it is, it is being partly diverted from its primary function, which is to make a kerf, and it won’t be as consistently accurate.

The hand without the saw can rest on the bench or work piece to aid in balance. It should bear the weight of no more than itself and the arm.

By the way, core activation does not mean being stiff. Think of the shock absorbers on a car. They are very strong but allow movement, always maintaining an equilibrium that allows all the other parts of the car to function smoothly and precisely. This discussion is about sawing with a backsaw but even with a handsaw where the entire body moves more, the core is still in primary control of all the motions.

Note to readers: Uncommon tips 1-6 can be found here. More on the way.

Corner blocks (corner braces) are a practical, effective way to strengthen furniture, particularly post and rail assemblies.

As previously discussed here, a properly designed and executed mortise and tenon joint will itself rarely fail but the wood around the mortise still can break. Two feet of leg extending below a table apron can impose huge leverage on the wood in the area of the joint.

Corner blocks are routinely used by chair makers but it surprises me when they are absent in tables where they could have been included. I use them whenever possible – belt and suspenders. Of course, sometimes there is no room for them, such as when a drawer is in the way, and sometimes they would disturb the appearance of the piece. The different mechanical stresses involved in casework make corner blocks generally less useful but there too they are still probably underutilized.

Working with tables

If the table aprons are at 90°, it is easy to make corner blocks with the table saw and miter gauge. The long side of the triangle could be as little as 3″ for a small table and 4 – 5″ or more for larger work. For thickness, 1 – 1 1/4″, using a single row of screws, is usually enough for small to medium work, though for large pieces, 2″ or more with a double row of screws is more in line.

I make corner blocks with a notch to accommodate the inner surfaces of the leg. I think it is best to leave a tiny gap between the block and the leg to avoid possible problems with wood movement that might affect the tenon shoulder line. However, in the past I have not always made a gap there and that has not caused problems.

If the aprons are not at 90° or are curved, I find it easiest to place a blank of wood diagonally spanning the aprons and simply trace the inside edges of the aprons and leg onto it, provided the top of the legs and aprons are flush. Then I bandsaw to the lines and, if necessary, refine the result with a plane. Alternatively, one straight cut, if required, could first be made on the table saw and used as a starting alignment. If the legs extend beyond top of apron, measure out and cut a notch, then place the blank and trace.

Another approach that is sound, though not my preference, is to make the block span the aprons but completely clear the leg. This sacrifices some glue area but should still be sturdy enough and seems easier to make.

Prepare the block by drilling and countersinking clearance holes for the screws. The center hole for the screw that will penetrate the leg is at 90° to the long edge of the block. I make the holes for the screws that will penetrate the aprons at 75°, not 45°, to the long edge of the block so there will be a good bulk of wood around the clearance hole. This also allows a little more screw length to penetrate the apron.

The blocks in the photo above show the features discussed.

I glue the blocks in place with Nexabond 2500M CA glue after sizing the end grain for about one minute, or similarly with quick set epoxy if the sawn surface is at all rough. After the glue sets, I drill pilot holes into the legs and drive those screws. Then I reset the masking tape depth stop and do the same for the apron screws, being extremely careful not to drill too far into the aprons.

If there is room for only a thin corner brace that cannot support a screw, a dovetailed attachment to the top of the aprons could be used. Otherwise, dovetailed attachments are difficult to make and unnecessary.

These are so eminently practical that it seems they should have been around for a century but it has been just several years since Lee Valley started manufacturing Chris Becksvoort’s clever idea. Since then, I’ve been using them whenever there is a need for a substantially long slot to accommodate the movement of a screw caused by dimensional changes in wood related to humidity.

One of the most common uses is for screws that go through cross grain support pieces and secure a table top. Another is at the back of drawer runners that are cross grain to the sides of a case.

The washers come in two sizes, designated #10 and #14, and both are thoughtfully made to convenient dimensions. The #10s shown here are slightly less than 1/2″ wide and 1″ long, with a slot slightly greater than 3/16″ wide. They are 3/64″ thick.

It is possible to rout slots for these but I find it easier to simply drill two 1/2″ holes with their centers 1/2″ apart using a Forstner bit in the drill press. Pare away the remaining web with a 1/2″ chisel. Next, without changing the fence setting, drill 3/16″ through holes on the same two centers. Then drill overlapping holes in between and gradually drill away the waste to form the slot.

The finished slots, and the washer and screw in place are shown below.

For this type of assembly, I prefer square drive, hardened, deep-thread, washer head screws, #8 in this case, available from McFeely’s. (Technically, this is a combo drive head but who in his right mind, given the choice, would use a Phillips driver instead of a square driver.) Of course, the depth of the large slot must be worked out according to the thickness of the stretcher or runner, the thickness of the piece that the screw will bind to, and the length of the screw. The view from the other side is shown below.

True, the same slot construction can be done without the washer and in fact, those that I have so made have functioned well for many years. And there are other good approaches to this issue. However, when sizable dimensional swings must be accounted for, it has always been too careful a setup done with some doubt about the possibility of the screw head binding. Perhaps if it was socked down too tightly in dry wood, I’ve wondered, it might get stuck in the swell of wood around it and not slide.

These washers make things simple and remove any doubts. The screw head will not catch on the metal washer. The construction is clean and sure. Thanks to Chris and Lee Valley for this handy hardware item that should be in routine use.

The glue line of a properly constructed mortise and tenon joint will almost never break from external load. Other things might break but not that.

To get a good sense of this, let’s think about what’s going on in just a small joint with a tenon 3″ wide by 1″ long. There are 6 square inches of glue surface, which is equal to that in an 8″-long edge joint between ¾”-thick boards. Now imagine trying to break that edge joint, not in tension as in hammering down on the unsupported joint line, but in shear! The wood will break, the glue line will not.

The mortise and tenon joint is strong because even in a fairly small joint there is plenty of glue line and it is stressed in shear. So if you’ve fit that decently, don’t worry; it is very unlikely to break. The tenon shoulders transfer much of the stress to that glue line. (By the way, the glue line of a half-lap joint can be stressed in tension if, for example, a frame undergoes severe twisting forces.)

The tenon itself is stressed mostly in tension and compression along the grain, which are also quite strong. So don’t worry there either, because a reasonably sized tenon is also very unlikely to break.

Furthermore, for the purpose of strength, there is no point in fitting the tenon tight to both ends of the mortise. That does not make the joint strong.

If something is going to break, it is most likely to be the wood of the stile or leg, which can succumb to stress in tension across the grain. This is especially so if the joint is designed with injudicious distribution of wood among the components.

Thus, make sure the stile or leg will be strong around the joint. In general, the walls of the mortise ought to be at least as strong as the tenon. And though it seems less popular lately, a haunch is a good idea when joining an apron at the top of a leg.

Also, hygroscopic cycle changes in the wood will stress every mortise and tenon but don’t let this be any more than it must. Don’t let a tenon and excess glue bottom out in the mortise and don’t jam a tenon to each end of the mortise (see above). Placing a peg too far from the shoulder will tend to make hygroscopic movement eventually produce a gap at the shoulder, though placing it too close to the shoulder will make the mortise wall more liable to break.

Inspecting old broken or cracked furniture and other wood structures, wherever you can find them, and thinking about why the failures occurred, is one of the most useful habits a woodworker can have. I’ve been doing this for several decades – I suppose because I would rather not have the same things happen to anything I make.