You built the box, stood it up, and it rocks. Or the diagonals disagree by a quarter-inch, or the door you just clipped on hangs with a taper you can see from across the room. Here is how to tell which of three problems you have, how to fix each one before the box goes anywhere near the wall, and why a box that was square on the floor can come out of square once it is installed.
Four boards screwed or cam-locked into a rectangle are a parallelogram waiting to happen. Nothing about a flat-pack cabinet is square on its own — it becomes square when every joint is pulled tight and the back is fixed with the box already true. Miss either and you get one of the three faults on this page: a box that is racked, a box that is twisted, or a box that is fine until the wall gets hold of it. All three are cheap to fix on the floor and expensive to fix once there is a countertop on top.
Measure both diagonals across the front of the box. If they agree to within about 1/16″, it is square; if not, back out the back-panel screws along one edge, push across the longer diagonal until the numbers match, and drive them home again. If the box rocks on a flat floor, it is twisted: loosen the joints at the high corner, press it flat and re-tighten by hand. And if it tests square on the floor but the doors taper once it is installed, the floor or the wall is racking it — fix the legs and the shims, not the box.
Do this to every box as you finish it, before it joins the stack. It takes less time than reading this paragraph, and it is the only way to find out whether the box is square while fixing it is still a matter of loosening screws.
Why an eighth of an inch matters: on a typical base box, a 1/8″ difference between the diagonals means the top of the box has shifted roughly 3/32″ sideways relative to the bottom over its 30″ height. A Euro hinge gives you about 2 mm of side-to-side adjustment — a little over 1/16″ — so an eighth on the diagonal is already more than the hinges can hide. A sixteenth is comfortably inside it, which is why it is the line.
A framing square reaches about 16″ up the side of a 30″ box. An angle a third of a degree out shows there as less than a tenth of an inch — the gap you talk yourself out of — and still puts the far corner of the box 3/16″ out. The tape across the diagonals sees the whole box at once.
The single most useful thing to know is where the box went out of square, because the fix is in a completely different place.
This is also why the install sequence checks level after every single box rather than at the end of the run. An error found on box two is a ten-minute fix. The same error found on box seven has travelled along the run and landed on the cabinet next to the fridge, where you will see it every day.
A flat-pack box has one moment when squaring it is effortless: after the sides, bottom and top rails are joined — screwed on a particle-board box, cam-locked on a plywood one — and before the back is fixed. At that point the box will rack in your hands, which is exactly what you want — it means it will also rack back.
On Flip boxes the back is a thin panel framed by solid material: on the particleboard build a ¼″ back sits inside ¾″ rails across the top and bottom of the rear; on the plywood build a thinner ⅛″ back is set into a full ¾″ frame. Either way, a back that is cut square and fully seated is a squaring jig you did not have to make — if it drops into its opening without forcing, the box is square, and if it will only go in at a slant, the box is not. The materials chapter has both builds panel by panel.
Found it late? It is still a floor job, and still quick.
A box that keeps springing back after you square it is being held out by something solid: a back panel sitting on a lip instead of in its rails, a screw driven at an angle, a fragment of melamine or carton trapped in a joint. Squaring will not beat it. Find it — run a fingertip along every joint line on the inside; a step you can feel is a joint that is not closed.
A twisted box can have perfect diagonals and still be wrong. One corner sits out of the plane of the other three, so the box rocks on a flat floor and, later, the door touches the box at three corners and stands off at the fourth. The hinges cannot fix this, because there is no adjustment that bends a door.
Once the box is on the wall, twist and floor are hard to tell apart, which is why the test belongs on the floor. In place, each leg should be wound down until it just bears — not until it lifts its corner — and the level goes across the box both ways after every one.
If the pre-drilled holes don’t meet, the parts are almost never mis-drilled. The panel is the wrong way round. Every Flip box is the same few panels going together in one sequence, and each panel can go in four ways, only one of which is right. Check these in order:
The rule that covers all four: never drill a new hole to make a part fit. A new hole beside a factory one leaves the panel weaker in exactly the spot that carries the load, and it almost always means the part is turned. Turn it, and the holes will be there.
And the screw that spins? A stripped hole in particleboard is the most common repair in any kitchen, and the instinct to reach for a fatter screw is wrong — it crushes more board and fails again a turn later. Toothpicks and glue for a small hole, a glued hardwood dowel or epoxy filler for a big one, then the original screw. The fix-it guide has the details.
And the cam that will not pull tight? On a plywood box the joint only closes when three things line up: the connecting bolt screwed all the way into its panel, collar flush; the cam turned so its opening faces the bolt before the panels meet; and the panels pushed together by hand first. Then turn the cam until you feel it bite and the joint close — turning past that point only loads the board. A cam that turns and turns without drawing the joint has either missed the bolt head (back it off, check the bolt is seated, try again) or is spinning in a housing that has been forced loose. Stop there: more force only crushes more board. A housing that was loose before you ever turned it is a quality problem for your Flip Kitchen sales rep, not a repair.
A box that tested square and then came out of square once it was fixed has been bent by one of three things, and they are worth checking in this order:
Uppers do the same thing on a wavy wall, with the extra trouble that the whole load hangs off the screws. If an upper’s doors taper after it is hung, start with the wall screws, then the joins to its neighbours. Uppers that don’t line up has the rest.
Most people find out a box is out of square from the door, not the tape measure. The symptoms are specific enough to read backwards:
| What you see | What it usually means |
|---|---|
| The gap beside a door is wider at the top than the bottom | The box is racked. The door is hanging square to gravity; the box is not. |
| A pair of doors meets in a V, or overlaps at the top | Racked box. Two doors magnify it, because each one takes half the lean. |
| The door touches at three corners and stands off at the fourth | Twist. Hinges cannot fix it; the box has to be flattened. |
| A drawer binds at one corner, or only when it is full | Racked box: the two sides are no longer parallel, and the weight closes the gap. |
| A drawer front tilts down as it comes out | Not the box. The drawer is not fully clipped onto its runners — pull it out and re-seat it until both clips click. |
| Every door in the run leans the same way | The run is out of plumb, not one box. Check the level and the legs before touching a hinge. |
Hinges are the last step, not the first. A Euro hinge gives you about two millimetres each way in three directions — a tuning range, not a rescue. Use it to even the gaps on a square box. On a racked box it only moves the taper somewhere else, and you can spend an hour chasing a problem that is not in the hinges. Chapter 05 has the hinge-tuning walkthrough for when the boxes are right.
A kitchen is fifteen to twenty boxes, and the habits that keep the first one square cost nothing on the rest.
When the boxes are square, the next thing that tends to go wrong is the arithmetic: a run that turns out longer or shorter than the wall. That is its own page.
Measure the two diagonals across the front of the box, corner to corner, with a tape measure. If they match to within about a sixteenth of an inch, the box is square. Then check for twist: stand the box on a hard, flat floor and press each top corner in turn. If it rocks, one corner is out of plane even though the diagonals agree.
Treat a sixteenth of an inch between the diagonals as square. At an eighth, the top of a typical base box has shifted about 3/32 inch sideways over its height, which is more than a hinge can hide, so fix it before the box goes on the wall. A quarter inch or more means something in the assembly is wrong, not just loose.
Usually the joints are not fully pulled up, or the box was built on a soft or uneven surface and set out of plane. Check every assembly screw or cam lock is snug and every panel edge sits tight against its neighbour. If one corner rocks on a flat floor, loosen the joints at that corner, press the box flat and re-tighten by hand.
Yes. Back the screws that hold the back panel out a few turns along one edge, push across the longer diagonal until both diagonals agree, then drive the back screws home again. The back is what holds the box square, so it has to be fixed with the box already square. Re-use the existing holes and drive them snug by hand.
Almost always because a panel is the wrong way round: upside down, swapped left for right, or with its finished edge facing the back. Check that the edge banding faces the front, the shelf-pin and hinge holes face into the box, and the runner holes sit at the same height on both sides. Never drill new holes to make a wrong panel fit.
Not unless the instructions call for it. Flat-pack boxes are designed to be held by their screws or cam locks, and glue in the end grain of particleboard adds little strength. It also takes away your chance to loosen a joint and square the box afterwards, which is the one correction you are most likely to need.
Do not go up a screw size; a fatter screw crushes more board. For a small hole, push in two or three glue-dipped toothpicks, snap them flush and drive the original screw back while the glue is wet. For a bigger hole, glue in a hardwood dowel or pack it with epoxy wood filler, let it cure, and drill a new pilot.
First check the drawer is seated on both runners until the front clips click. If it is, measure the box diagonals: a racked box pulls the two sides out of parallel, so the drawer binds at one corner, often only when it is loaded. Square the box and the drawer usually runs again without touching the runners.
Usually the bolt is not fully seated or the cam is not engaged. Screw the connecting bolt in until its collar sits flush with the panel, turn the cam so its opening faces the bolt, close the joint by hand, then turn the cam until it bites and draws the panels together — snug, then stop. If the cam spins without tightening, the board around its housing is crushed and more force only makes it worse; that joint needs repairing or the panel replacing.
Two diagonals per box, checked before the back goes on, is the cheapest insurance in the whole kitchen. Every door you hang later depends on it.
The assembly sequence →