Attaching a solid-wood top so it can move

Buttons, tabletop clips, figure-8 fasteners and slotted screw holes: how each lets a solid top expand and shrink across its width, and how to lay them out.

A solid-wood top changes width with the seasons. The aprons under it barely change length. Screw the two together rigidly and the top will crack, cup, or pull its fasteners loose within a few years.

The fix is to hold the top down firmly while letting it slide across the grain. Four methods do that well. Each is simple; the part people get wrong is the layout.

How much will it move?

Start with an estimate. For a flatsawn top, width × tangential coefficient × change in moisture content gives the total change across the top. A 20-inch red oak top over a 4-point seasonal swing:

20 × 0.00369 × 4 ≈ 0.30 inch, a little under 5/16 inch in total.

If the top is fixed at its centre, each edge moves about half of that, roughly 5/32 inch. The coefficients for other species are in wood movement.

Four ways to fasten a top

Wooden buttons

A button is a small L-shaped block. Its tongue sits in a groove or short mortise cut in the inside face of the apron, just below the top edge, and a screw through the block goes up into the top.

On the aprons that run across the top’s grain, the button slides in and out of its groove as the top moves. Leave a gap between the end of the tongue and the bottom of the groove, at least as large as the expected movement at that point.
On the aprons that run along the grain, the button slides along the groove.
Make the block so that its tongue sits a little below the top of the groove when the top is in place, about 1/16 inch. Tightening the screw then pulls the top down against the apron.

Buttons are cheap, strong and invisible. You can make dozens from offcuts.

Tabletop clips (Z-clips)

Steel clips shaped like a flattened Z do the same job as buttons. One lip sits in a saw kerf cut in the inside face of the apron, and the other is screwed to the top. The kerf is commonly cut with a biscuit joiner or on the table saw, all the way along the apron or just where each clip goes. Check the clip maker’s kerf width and distance from the top edge.

Clips are fast to install and are a good choice when you are fastening many tops or cannot cut a continuous groove.

Figure-8 fasteners

A figure-8 (or desktop) fastener is a flat steel plate with two holes. One end is set into a shallow counterbore drilled in the top edge of the apron and screwed down; the other end is screwed to the underside of the top. The plate pivots as the top moves.

Pivoting accommodates only a modest amount of movement, so figure-8s suit narrower tops or positions near the fixed centre. Turn them so the swing runs across the grain of the top.

Slotted screw holes

Screws through the aprons, or through cleats fastened to them, can hold a top if the holes allow movement. Drill the holes as slots elongated across the grain of the top, and use a washer or a pan-head screw so the head can slide. Only the hole at the fixed point should be round.

This method is common under breakfast-bar tops and in cleats across the ends of wide tops.

Where to fix the top

A top that is free everywhere can creep. Fix it at one line and let it move away from there:

Centre fixing is the default. Fasten the top rigidly at the middle of the end aprons, with a screw through a round hole or a snug button. Movement splits evenly toward the front and back.
Back fixing suits tops against a wall, such as a hall table or a desk. Fix along the back so all the movement goes toward the front and the back edge stays tight to the wall.
Front fixing keeps a consistent overhang over a drawer front or a face frame.

Layout

Space fasteners every 8 to 12 inches along each apron, and within a few inches of each corner.
Place the ones on the across-grain aprons with their slack in the direction the top will travel. A top built in a dry winter will grow; one built in a humid summer will shrink.
Remember the overhang. A top that grows by 1/4 inch toward the front changes how far it overhangs a drawer front.
Finish the underside as well as the top. It does not stop movement, but it slows moisture exchange on both faces equally, which helps the top stay flat.

Plywood and veneered tops

Plywood, MDF and veneered-core tops are dimensionally stable across their width. They can be glued, screwed through round holes or pocket-screwed without allowing for movement.

In GrainDraft

The starter side table on the GrainDraft homepage has a top that is deliberately not joined in the model. Its shop packet says so and leaves the fixing method to you: this article is that method. When you model your own piece, check each wide solid part’s grain direction and what it is fastened to across that grain before you choose a joint.

Numbers here are starting points from common shop practice and published references. Check your own stock, tools and hardware instructions, and cut a test piece before committing project wood. Spotted an error? The contact address is on the About page.