French cleat: the bevel that hangs on the wall

You have a wall, and you want to hang things off it — a shelf, a bin of fasteners, a screwdriver holder — and you want to be able to move them tomorrow without drilling again. The French cleat solves precisely that problem, and it does so with the simplest piece of joinery imaginable: a batten with one edge cut at an angle. The trick isn't the shape, which is trivial, but the way that shape distributes the weight. And when that batten stops being wood and comes off your printer instead, the bevel forces you to think about two things that used to let you off the hook: which way the layers stack, and how much gap you leave at the contact. That's what this article is about.

Two bevels facing each other

A French cleat is two identical battens with one bevelled edge, mounted facing each other. The wall batten is screwed on with its bevel pointing up and in, forming a ramp that rises against the wall. The batten on the thing you hang — your shelf, your holder — carries its own bevel pointing down and in. You drop the piece in from above, the two bevels find each other, and it hangs there, resting one sloped face against the other.

That's the whole mechanism. No screw holds the piece to the wall, no clip clicks home: the piece sits on the bevel of the fixed batten under its own weight. Because the engagement is nothing but geometry, you can lift it off by a couple of centimetres and set it down again thirty centimetres along, on the same batten or a different one. That is exactly what the system is for: a wall full of interchangeable anchor points.

Why the weight pushes against the wall

The bevel angle isn't decorative. When two surfaces at 45 degrees rest against each other, the weight of the hung piece doesn't drop straight down: the sloped face splits it. One part pulls downward, following the ramp; the other pushes the piece horizontally against the wall. At 45 degrees those two components are equal: every kilo you hang generates a kilo of thrust pressing the piece into the wall.

That's why the piece stays pressed against the wall under its own load, with no latch that could give way. But beware the obvious conclusion: that thrust only keeps the piece against the wall — it gives you no margin of safety. More weight does not mean more grip against the real failure modes; on the contrary, it loads the root of the bevel more heavily and pulls harder on the wall screws. The piece lifts off and unhooks just as easily, loaded or empty.

The de facto standard angle is 45 degrees. Sometimes the bevel is cut shallower, at 30 degrees from horizontal, and here it pays to distrust your intuition. A shallower ramp doesn't press harder against the wall — it presses less: at 30 degrees the horizontal component is W·tan 30° ≈ 0.58·W, against a full W at 45 degrees. In return, it needs less vertical travel to unhook, and it leaves a thinner, more fragile edge that, worse, no longer self-supports when you print it. For FDM, 45 degrees is the comfortable angle: it's exactly the limit most printers handle without support, so the bevel prints in mid-air, with no bridges and no support material to pick off.

The pitch: a wall full of parallel battens

A single batten will hold on its own, but the system comes into its own when you fill the wall with parallel battens at a regular pitch. That pitch — the vertical distance from one batten to the next — is what lets you reposition accessories at different heights. The piece you hang only needs a stretch of cleat resting on any one of the battens; the whole wall becomes a grid of hook points.

Typical pitch runs from 100 to 200 mm. Closer together, more possible positions, but more batten (and more screws into the wall) per square metre; further apart, less material, but coarser jumps in height. It's worth being honest about what is and isn't a standard here.

Printing the cleat without the layers splitting

This is where FDM changes the rules. A hung piece loads its bevel permanently, and in FDM the direction of the load relative to the layers is everything. The bond between layers is the weak point of any printed piece: within a layer the material is continuous, but between one layer and the next there's nothing but the weld the hot new bead formed against the cold layer beneath it. Pull along the layers and it holds; pull to separate them and it peels apart like the pages of a book.

A hung accessory pushes its bevel down and away from the wall. If you print the male cleat lying flat, with the layers stacked in the plane of the bevel, that load pulls in exactly the direction that separates the layers: the cleat flakes off and the piece falls, almost always with a load on it. The rule is to print the cleat standing up, with the layers running along the bevel and the wall, so the weight travels within the layers rather than prising them apart.

The 45-degree bevel works in your favour on another count: it's self-supporting. Printed in the right orientation, the sloped face is a 45-degree overhang the printer handles without support, so the contact surface comes out clean and free of the scars support material would leave — scars that would spoil the bevel's seat anyway. Add several perimeters in the cleat area and don't leave it hollow: that's the part doing the work.

The bevel's clearance: seats without forcing, sits without wobble

Bevel against bevel is a contact of two flat sloped faces, and in FDM that contact ends up tight if you draw it to nominal size. As with any printed fit, the process fattens the faces: material deposits toward the gap. The male bevel comes out a touch thicker and the female one a touch tighter. What was a snug contact on screen is interference in the part. The physical reason for that bias — holes that shrink, bosses that swell — is in Real printed clearances.

The practical upshot is that you need to leave a small clearance in the plane of the bevel so the accessory drops in and seats without forcing. Since this contact doesn't move once hung — it doesn't slide or turn, it only rests — it's a fit for position, not for motion: you want the gap just big enough that it goes in by hand and sits firm, not so big that the piece rocks under load. In PLA, something like 0.1–0.15 mm per side on the bevel face is a good starting point; measured across the gap between the two ramps, not as a diametral dimension. To pick that family of fit with confidence, Choosing the fit: clearance, transition, interference works through the reasoning.

One thing the bevel geometry alone won't give you is a stop to keep the accessory from sliding further down. If you let the male cleat slide unchecked down the ramp, the piece drops until friction stops it, and its final height depends on the clearance and the weight — which means it isn't repeatable. Add a horizontal shoulder on the back of the accessory, below the cleat, that butts against the lower edge of the wall batten once the piece has dropped by just the right amount. That stop fixes the seating height and, in the process, carries part of the load in clean compression against the batten instead of leaving it all on the bevel.

Hooks, shelves and boxes: the male cleat on the back

You now have everything a hangable object needs: a male cleat on its back, oriented and printed as described. A tool hook is a body with the cleat behind and an arm in front; print it so that both the cleat and the arm carry their load along the layers, because the arm is also a cantilever hanging weight and suffers the same delamination failure at its root. Fillet both roots.

A shelf is the same thing at a larger scale: a tray with one or more male cleats on the back edge. If it's wide, spread two or more stretches of cleat so they rest on the batten at several points and the shelf doesn't twist. But be careful about taking "standing up" to a large scale: a wide shelf printed on its edge is a tall, narrow piece with little base on the bed, prone to tipping during the print and to hitting the Z height limit. When the cleat won't fit standing up, print it as a separate part — standing up, with its layers well oriented — and screw or glue it to the tray, or tilt the whole thing to bring the layers closer to the load direction. A box or bin hangs the same way, with the cleat built into the back wall.

In every case the same discipline holds: cleat standing up, layers along the load, fillet and thickening at the root, position clearance on the bevel, and a stop that fixes the height.

And one last check before you print the whole batch: measure the batten on your wall and run off one test piece. If the real angle of your batten isn't exactly what you assumed, or if your printer leaves the bevel tighter or looser than you expected, you'll see it in that first piece and adjust the clearance before spending filament on ten. To dial in that gap methodically rather than by eye, Real printed clearances explains how to measure it once and reuse it.