How cabinet panels are joined, and why the fixing matters more than the board
Cabinets fail at their joints far more often than they fail in the middle of a panel, and almost every joint problem traces back to the same physical fact: the cut edge of a sheet is the worst place in the board to put a fixing. Everything else in this subject, from dowels to cam locks to the connectors we use, is a different answer to that one problem.
A screw into a board edge has almost nothing to grip and gives up after a couple of reassemblies. Glued dowels are strong and permanent. Cam locks come apart repeatedly and still bore into the edge. Face-fixed connectors put every hole in the face of the panel instead, which is the strong direction, and they can be undone and redone without ruining anything. That last one is what we build, and the reason is mechanical rather than fashionable.
The problem every joint is solving
Take a sheet of faced chipboard and look at the cut edge. Inside the skin is a loose matrix of wood particles and resin with air between them. Drive a screw into that and the thread is trying to grip something with the consistency of a firm biscuit, in the direction that crumbles most easily.
Drive the same screw through the face of the board and it is a different situation entirely: it passes through the dense pressed material and the skin, across the grain of the panel rather than into its weakest plane.
That difference explains a lot of furniture. It is why a flat-pack bookcase loosens where the shelf meets the side, why the same cabinet survives one house move and not two, and why a screwed drawer box is the weakest of the constructions. Solid wood and plywood behave far better in the edge, which is one of the practical differences covered in the materials comparison.
Five ways to make the joint
Joint
How it works
Comes apart?
Where the holes go
The catch
Screws into the edge
A screw driven through one panel into the edge of the next
Once or twice, and it loosens each time
Through the face of one panel, into the edge of the other
The edge of a board holds a thread poorly, and it gets worse with every reassembly
Glued dowels
Wooden pins in matching holes, glued
No. The glue line is the joint
Into the edge of one panel and the face of the other
Permanent, and it needs accurate drilling and clamping while the glue sets
Cam lock (minifix style)
A bolt into the edge of one panel, engaged by a cam turned in the face of the other
Yes, repeatedly
Into the EDGE of one panel and the face of the other
Edge boring, which needs accuracy and puts the fixing into the weakest part of the board
Face-fix connector
A connector in a pocket routed into one face, with its screw driving into the face of the other panel
Yes, and that is what it is designed for
From the FACE only, on both panels
A visible cover cap on the inside face, and the pocket needs the right machining
Dado or groove
A slot machined across one panel that the other sits in
No, once glued
A machined slot rather than holes
Traditional and strong, and it removes material from the panel carrying the slot
Read the fourth column rather than the first. Every joint here is decided by where its holes go, and the ones that bore into an edge inherit the weakness of that edge no matter how good the hardware is.
The cam lock, which is better than its reputation
The cam lock, familiar from flat-pack furniture as a metal disc with a slot in it, is a genuinely clever mechanism. A bolt screws into the edge of one panel, its head passes into a hole in the face of the other, and turning the cam draws the two together with real clamping force. It comes apart and goes back together as many times as you like.
Its weakness is not the mechanism, it is the boring. The bolt goes into the edge, which is the plane we have just established is the weak one, and the accuracy required is high: the bolt hole, the cam hole and the panel edges all have to line up within a small tolerance or the joint pulls crooked.
Done properly it is a good joint, and most of the cheap furniture that gives cam locks a bad name is suffering from loose tolerances and thin board rather than from the connector.
Face-fixed connectors, and why we use them
The connector we fit sits in a pocket routed into the face of one panel, and its screw drives into the face of the other. Nothing is bored into an edge at any point. That single property is the argument, and it has three consequences:
The fixing is in the strong direction. Both halves of the joint are holding in pressed board through the face rather than in the crumbly edge.
It is properly demountable. The connector is designed to be undone and redone, so a cabinet can be flat-packed, assembled, taken apart for a move and reassembled without the joint degrading.
The machining is simpler and more repeatable. Everything happens from one side on a flat panel, which is exactly what a CNC does well, and there is no edge drilling to go off square.
The numbers, for anyone who wants them. Our corner connector sits in a pocket about 33.8 by 16.5 mm and 10.8 mm deep, cut with a Ø12 router cutter or made from a row of overlapping drilled holes, and its screw goes into a Ø5 by 12 mm bore in the mating panel. It suits board from 13 mm thick, its axis stays at least 20 mm from the panel edge, and connectors on a joint sit between 200 and 300 mm apart. The manufacturer publishes holding figures of roughly 880 N in tension and 830 N in shear per connector.
Those published figures are laboratory values for the connector, and the honest way to use them is with a margin. When our own software sizes the rear braces that keep an open-backed cabinet square, it works from roughly 500 N of service shear per connector in 18 mm board, which is about half the published number. That gap is the difference between what a part can do once and what you design around.
The visible cost is a cover cap on the inside face of the cabinet. You see a small disc where each connector sits, which is the trade for having no edge boring anywhere.
Dowels and dados, which are not obsolete
Neither of these comes apart, and both are excellent.
Glued dowels are what a cabinet shop uses when the piece is being built in place and will never be moved. The glue does most of the work and the dowels align the panels and stop them shearing. The result is rigid and permanent, and it needs accurate drilling and clamping while the glue cures, which is why it belongs to workshops rather than to flat packs.
Dados are older still: a slot machined across a panel that the mating panel sits in. A shelf in a dado is supported along its whole width rather than at four points, which is why traditional bookcases hold their shelves so well. The cost is material removed from the panel carrying the slot, and, again, permanence.
The pattern worth taking away: joints that come apart are convenient and joints that do not are usually stronger. A flat-packed cabinet chooses the first on purpose, and a fitted piece of joinery chooses the second.
Where the joints go, and how many
Two things about spacing are worth knowing, because they explain why a parts list has the number of connectors it does.
Too close is a real failure. Connectors crowded together put several stress concentrations into a short stretch of board, and the board between them can break out. That is why there is a minimum spacing as well as a maximum, and ours is 200 mm.
Too far apart lets the joint open. Between fixings the panel can flex away from its neighbour, so a long joint with two connectors at the ends behaves like a hinge. Hence the 300 mm maximum, and hence a taller cabinet getting more connectors rather than bigger ones.
The same logic drives the boards across the back of an open cabinet: two rows of connectors at each end of a board form a couple, and the width of the board is the lever arm. The back panel guide works through that, and it is a nice illustration that joinery is geometry rather than brute strength.
What to look for when buying
Ask where the holes go. Edge boring or face fixing tells you more about how the cabinet will age than the brand of the board.
Ask whether it comes apart. If you might move, that is worth real money, and if the answer is dowels, plan to keep the cabinet where it is.
Look inside a corner. Cover caps, cam discs, dowel plugs or nothing visible at all: each tells you what you are getting.
Count them. Two fixings on a metre-tall joint is a hinge with ambitions.
The connectors are in the parts list
Every joint in a design you draw resolves into connectors with real positions and a count, which is why a taller cabinet costs a little more than the boards alone suggest. Change the size and the joinery is recalculated with it, before anything is machined.
With knock-down connectors rather than glue and nails, which is what lets a cabinet ship flat and go together with a hex key. The common types are cam locks, familiar as a metal disc with a slot in it, and face-fixed connectors that sit in a pocket routed into the panel face. The key difference between them is where the holes go: a cam lock bores into the edge of one panel, while a face-fix connector puts every hole in the face, which is the stronger direction in sheet material and the reason we use them.
Why do screws into chipboard come loose?
Because the cut edge of a board is the weakest place in it. Inside the faced skin is a loose matrix of wood particles and resin with air between them, so a thread driven into that edge is gripping something with the consistency of a firm biscuit, in the direction that crumbles most easily. Every time the joint is undone and redone, more of that material breaks away. The same screw driven through the face of the panel passes through dense pressed material and holds far better, which is the whole argument for face-fixed joinery.
Are cam lock cabinets any good?
The mechanism is better than its reputation. A bolt screws into the edge of one panel, its head enters a hole in the face of the other, and turning the cam draws the two together with real clamping force, repeatedly and without damage. The weakness is not the connector but the boring, since the bolt goes into the edge, which is the weak plane, and the tolerances are tight enough that sloppy manufacturing pulls the joint crooked. Most of the flat-pack furniture that gives cam locks a bad name is suffering from thin board and loose tolerances rather than from the fitting.
What is a face-fix connector?
A knock-down fitting that is machined entirely from the face of the panel rather than into its edge. The connector sits in a shallow pocket routed into one panel, typically around 34 by 16 mm and 11 mm deep, and its screw drives into a small bore in the face of the panel it joins. Because nothing is bored into an edge, both halves of the joint hold in the strong direction, the machining is simple and repeatable on a CNC, and the joint can be undone and reassembled without degrading. The visible cost is a cover cap on the inside face.
How strong are cabinet connectors?
The connector we use publishes roughly 880 newtons in tension and 830 in shear per fitting, which are laboratory figures for the part itself rather than a promise about a finished cabinet. The honest way to use numbers like that is with a margin: when our software sizes the rear braces that keep an open-backed cabinet square, it works from about 500 newtons of service shear per connector in 18 mm board, roughly half the published value. That gap between what a part can survive once and what you design around is normal engineering practice.
Are dowels better than connectors?
Stronger, and permanent, which makes them better for something that will never move and worse for anything else. Glued dowels rely on the glue for most of their strength while the dowels align the panels and resist shearing, so the result is rigid and cannot be taken apart without destroying the joint. That suits a cabinet built in place by a workshop. A knock-down connector trades some ultimate strength for the ability to flat-pack, assemble, dismantle for a house move and reassemble, which for most people is worth more than the difference.
How many connectors does a cabinet joint need?
Enough that the panel cannot flex open between them, and not so many that the board breaks out. Ours sit between 200 and 300 mm apart along a joint, with the axis at least 20 mm from the panel edge. Too close and several stress concentrations crowd into a short stretch of board; too far apart and the joint behaves like a hinge, with the panel flexing away from its neighbour between fixings. That is why a taller cabinet gets more connectors rather than bigger ones, and why the count appears in the parts list as the design changes.
