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Methods that allow the wood to move with the seasons.
Aabout ten years ago, I made a folding table for a project book. When it came time to mount the top, I just drilled pilot holes and inserted the nails cut through the top into the aprons. Are you horrified? In fact, the approach worked great. In the years since I assembled it, the top has remained healthy and firmly attached to the aprons. And while I don’t hesitate to use this approach when the circumstances are right, such as on a casual kitchen table, there are many better ways to mount a table on its stand.
You can attach a tabletop to its stand with blocks firmly glued to both the aprons and the tabletop. This does not allow the tabletop to expand and contract, of course, and the resulting stresses will eventually split or bend the top.
And herein lies the challenge: how to prevent the continuous expansion and contraction of the wood from destroying the assembly or itself. The table top must be held firmly to the leg assembly, but in a way that allows the table to expand and contract.
Most carpenters know this, of course, and I think that’s why so many of them cringe at the thought of nailing the tabletop to its support. Okay, it could also be an affront to their aesthetic sensibility.
To make it a little easier, let’s assume here that the grain of the tabletop is square compared to a straight leg and apron support. That is, two of the aprons are parallel to the grain of the tabletop and two are perpendicular to it. The shape of the top – square, rectangular, round, oval, free-form – has nothing to do with this. The direction of the grain, and therefore the direction of expansion and contraction, is what is important.
If you are building a table with curved aprons or without aprons, you will need to extrapolate from my examples to fit your specific design.
Glue and screw blocks
An improved version of the glue block method is to attach log blocks or strips to the aprons, then insert screws through them into the tabletop. This is an excellent approach, as long as properly oriented, elongated pilot holes are used to allow for seasonal expansion and contraction of the wood.
First of all, the grain of the blocks should be parallel to the grain of the apron. The movement of the wood has no impact here, so you can glue, nail or screw the blocks to the aprons. But before you do that, ream the drivers for the screws – you want to use screws, not nails – to secure them to the tabletop.
At the center of the cross-sliding block is a “fixed pilot”, a hole matched to the diameter of the screw. This screw secures the tabletop to the leg assembly; all movement occurs on both sides of this point. Beside the fixed pilot there should be pilot slots parallel to the grain of the block.
Blocks that run parallel to the grain of the tabletop must have only pilot slotted holes and must be oriented transversely to the grain.
Being a steady pilot is, of course, simple. Make a hole. But creating the slots is more of a challenge. Typically, I use a file 3⁄16”Twist drill in pillar drill. I place the block with a thin (low) fence fixed to the table.
Drill holes to delineate the ends of the crack, then nibble the debris between them. A little twist, of course, slips off the wood in one or the other of the holes, but it doesn’t take long to form a trench. Lock the pen and slide the work back and forth along the fence to tidy up the gap.
With the right type of screw, one with a washer-like head, you can use 1⁄4“- large slot, which you can easily produce with a Forstner bit. This is a little less demanding than using a twist bit, because a Forstner doesn’t move. Even if I’m a dedicated router user, it doesn’t. I see it as a router work. The diameter and length of the drill bit needed – 3⁄16” for 1⁄4“- makes routing an uncertain proposition, in my opinion. You also need two configurations, one for the cross grain slots, another for the long grain ones.
If I were to approach it as a router job, I’d route the slots into a wide board, then tear the strips off it. Then I’d arrange the slots and use an edge guide to place the long grain cuts and guide the router. Then, use a T-square to guide the cross cuts. Observe only the beginning and end of each slot and create each slot with a series of cuts, each dipped progressively deeper.
It is quite common these days to skip blocks and drill oversized pilot holes directly into the forecourts. You can slide long screws up through the edge of an apron and into the tabletop, or through angled pockets cut into the inside face of an apron. The latter approach works best for me, because it allows me to use shorter screws.
Making pockets and pilots is easier if you have a pocket jig and related accessories, but it’s not the only way.
With a drill press and a Forstner bit, you can make very neat and uniform pockets. Arrange the positions of the pockets on the apron. Send a Forstner bit into the drill press: I usually use a bit 1⁄2“size. Hold the apron at an angle and puncture the pocket. The tip design allows it to cleanly cut the wood to form a flat bottom pocket.”
The real trick here is to set and maintain the apron at a right angle. You usually see the apron cradled in an elegant tailored mask. Is such a mask worth it for the occasional project? I do not think so. I use two fences: one is upright to rest the apron, the second is a flat trap placed against the bottom edge of the apron to keep it at the correct angle.
I establish the angle by spreading it over the end of a scrap of the butt of the apron. I usually put a small rule at the end of the deviation and draw an eyeball angle from the center of the edge to a point 11⁄2“A 2” on the inner face. If you prefer to use a sliding bevel, set it to about 15 °.
Put a twist bit in the drill press, lower the bit almost to the table and lock the pen. Align the layout line with the tip, setting the fence vertical so that the apron is angled just to the right. Then slide the trap fence against the apron to prevent the bottom edge from sliding forward and changing the angle. Switch to the Forstner tip, put an apron in place, then puncture the pockets.
Once you’ve punctured all your pockets, go back to a bit of a twist and bore the riders. Most of these pilots need to be stretched, of course, but with pockets, this is usually achieved by swinging the drill to expand the exit hole. You can’t do this with the pillar drill, so switch to a hand drill. Rock the drill parallel to the aprons which will be along the grain of the tabletop and through the aprons which will be parallel to the grain.
Buttons are better
And there is yet another solution, and that is the one I often use when building a table. Use “buttons” spaced around the tabletop inside the aprons. A button, often called a cabinetmaker’s button, is a small block, roughly 11⁄4“Square and 3⁄4“Or less often. It has a tongue, which slips into a groove cut in the apron. Then you drive a screw through the body of the button into the tabletop. Over time, as the tabletop expands and contracts,” the button moves with it.As it does, the tongue moves along, or in and out, its groove in the apron.
The apron grooves can be through or interrupted. Some use the grooves in the aprons that go through the grain of the tabletop, because the tab of the button will move along the groove. But they use firm grooves in long-grained aprons, imagining the tongue moving in and out here. I tend to use still grooves all around. I’ll divide the length of a long apron by three or four buttons, but I’ll only use one in the center of a short apron.
The through grooves can be cut on the table saw or milled with a straight bit or a groove cutter. Stopped grooves are a router proposition, or you could use a biscuit joiner.
To ensure that the tabletop is held securely to the holder, design the button so that its shoulder is slightly shorter than the space between the top edge of the apron and the groove. When screwed to the tabletop, the button should be tilted slightly. The tongue should be slightly thinner than the width of the groove. To match the tone, you may need to blunt the tip of your tongue.
First, calculate the thickness of the button you need, grind a scrap board and cut a groove on each end. Cut a strip of about 1 1⁄4“Long from each end, then tear the strips into buttons about 1” wide. Drill a pilot hole through the body of each button.
With any of the fastening methods I’ve described – glue and screw blocks, screws in pockets, buttons – final assembly involves setting the tabletop, face down, on the counter. Flip the leg and apron assembly over and line it up at the top. Then drive the mounting screws.
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