The doors were 3 mm out of parallel, and every part of them was in tolerance

The situation

A European hotel group ordered 120 three-door sideboards from a factory in Foshan for a refurbishment programme. Each cabinet was 1,800 mm wide, 900 mm high and 400 mm deep: 18 mm MDF in an oak veneer, two vertical dividers, full-overlay concealed hinges with a soft close, two hinges per door. The order was worth $43,200, and 70% of it was still unpaid when the cabinets were finished, packed and photographed.

The purchase order carried one line about the doors: reveal between adjacent doors 3 mm, even. There was no other requirement anywhere in the document for the doors. The line was written the way thousands of furniture purchase orders are written, and it was accepted without comment by both parties.

The factory's own final check on each cabinet was thorough by the standards of the trade. The cup holes were verified on the boring line against the jig's own setting, so a cup drilled off the jig would have been caught before the door was hung. Every hinge was tested for opening angle, damping and closing force. The doors were hung and closed, and the doors closed.

The buyer booked an inspection before the balance was released. The inspector found the reveal between the doors was 1.5 mm on one joint and 4.5 mm on the next, on every unit sampled.

Every check was on a part, and the reveal is a property of the assembly

No one had, on either side, a number for the gap between the doors. The order said 3 mm, even, which is a statement of intention rather than a criterion of acceptance, and it did not say who measures it, where on the joint, with what, or what happens if the reading changes with height. So the reveal was checked informally, by eye, in the finishing room, by people with 120 cabinets to close and pack.

This is where a reveal is different from almost every other characteristic in a furniture order. A gap does not belong to a door. It belongs to the relationship between two doors that were cut on different days, hung on hinges out of a different carton, and closed against each other in a carcass assembled by a third pair of hands. Every component of that relationship can pass and the relationship still be wrong.

The parts here were not merely passing. They were passing with room to spare, and the reason they were passing is the reason the whole thing was missed. The cup holes were verified against the jig's setting, so they were bored exactly where the jig said. The hinges were the specified model. The doors were the specified width on the specified 18 mm leaf. Somebody checking the order for conformity would have found nothing to complain about.

How the reveal has to be measured

The arithmetic that closes the case is worth writing out. In the design, the cabinet is 1,800 mm wide: 1.5 mm of reveal, 597 mm of door, 3 mm of reveal, 597 mm of door, 3 mm of reveal, 597 mm of door, 1.5 mm of reveal. In the goods, the doors are the same 597 mm and the cabinet is the same 1,800 mm, so the four reveals still have to add up to 10 mm. They do. They were 1.5, 4.5, 1.5 and 1.5 mm, in that order.

**The sum was right and the distribution was wrong.** Nothing had been cut short, nothing had been made narrow, and no width was out. One door was simply sitting 1.5 mm from where it belonged, and because it is a rigid body hung from one edge, it took 1.5 mm out of the joint on one side and put 1.5 mm into the joint on the other.

The hole system everyone writes down, and the one that sets the reveal

Almost every cabinet order mentions the 32 mm system, and mentioning it is not a small thing. It is the row of 5 mm holes, 32 mm apart, drilled up the inside faces of the side panels and dividers, with the first row 37 mm back from the front edge. Hinge mounting plates, shelf supports and drawer runners all screw into that grid, which is why a replacement hinge made in one European factory will fit a cabinet made in another.

What the 32 mm system does not do is set the gap between two doors. It sets the height at which a hinge sits and how far forward the hinge body stands. Those numbers are visible and easy to check. The reveal is set on the other side of the hinge, on the door, and the order usually says nothing about it at all.

The door side has its own set of numbers. The cup hole is 35.0 mm in diameter and 13 mm deep. The two fixing holes are 45 mm apart. The cup centre sits 76.2 mm from each end of the door. The leaf is 18 mm thick, which leaves 5 mm of material in front of a 13 mm cup.

And then there is the one number that decides the reveal: the distance from the door edge to the cup hole. Hinge manufacturers publish it as a range, typically 3 to 7 mm depending on the model and the opening angle, because that is the adjustment which lets one hinge article produce a different overlap without a different part. **A manufacturer publishes a design range, not a manufacturing tolerance.** It is a menu. A factory that treats a menu as a tolerance has made a mistake that no inspection of the parts will ever find, because every hole on the line is exactly where the jig put it.

The single most useful thing to put in a cabinet order is the drilling distance as a single number with the hinge model named beside it, so that the decision about overlap stays with the buyer rather than with whoever set up the jig that morning.

What 'within tolerance' actually covered

Every measurable thing about this order was conforming. The jig was set to 4.0 mm for the middle doors and 5.5 mm for the outer doors, and the boring line verified each door against the jig, so each cup was bored exactly where the jig said. Both settings were inside the manufacturer's published 3 to 7 mm range. The cup diameters were 35.0 to 35.1 mm, the depths 12.9 to 13.0 mm, the fixing hole spacing 45.0 mm, the cup centres 76.2 mm from the door ends. The carcase hole pattern was the standard 5 mm at 32 mm, 37 mm from the front edge, on every panel. The hinges were the specified model, the doors were the specified width, on the specified 18 mm leaf.

That is the whole of the factory's position, and it is not a weak one. If you had ordered a hinge and received a hinge, and a jig setting and received that jig setting, you would have no complaint. What you had bought was a set of parts that each matched a drawing. What you were going to live with was a cabinet whose doors did not line up.

The gap between those two things is the whole case. A reveal is an output of the assembly, so it has to be accepted on the assembly. A tolerance on a cup hole describes how accurately a hole was bored. It says nothing about where the door ends up when that hinge is closed onto a mounting plate 37 mm back from the front edge of a divider, in a carcass that was assembled in a different week from the doors.

There is a second reason the tolerance held here, and it applies to every order: the error is small. 1.5 mm on a 1,800 mm cabinet is 0.08% of the width. It is inside the noise of a tape measure, invisible in a photograph taken from two metres, and on a veneered door in a warm corner of a hotel it reads as a shadow rather than a fault. Nobody signs off a shadow.

Where the honest limit sits

What the inspection established: that on 20 cabinets sampled from a lot of 120, the reveal between the first and second doors measured 1.5 mm and the reveal between the second and third measured 4.5 mm, at all three heights, on every unit; that the outer reveals measured 1.5 mm; that the three doors were 597.0 mm wide and the cabinet 1,800 mm, so the geometry added up exactly and the fault was in position rather than in size; that the three door fronts were coplanar within 0.3 mm; and that the cup holes in the middle doors were bored 4.0 mm from the door edge against 5.5 mm in the outer doors, with every other cup dimension conforming.

What the inspection did not establish: why the two settings differed. The factory's boring log records the jig fence position for each batch, and it shows the middle-door batch for this order at 4.0 mm and the outer-door batches at 5.5 mm, and it records nothing about who moved it or when. The report entered that log as the factory's account of the cause and did not adopt it as a verified fact, because the log is the factory's own document and nobody in the finishing room could say what the 4.0 mm was set for.

What the inspection could not establish: whether other orders in the same week were bored with the same wrong setting, and how the cabinets would behave in service. The tight joint left the middle door's free edge in contact with the neighbouring door over most of its height, and whether that turns into a door that will not close after a winter depends on the leaf's movement and on the door's own bow, neither of which is a fixed number. The report said so, and recommended that the buyer decide on replacing the middle doors rather than relying on the hinge adjustment to recover 1.5 mm.

One point of method is worth stating, because it is the one most reports get wrong. The reveal here was not a random characteristic that happened to fail. It was produced by a setup that was identical on every unit in the run, so it is a lot-level fact, not a count of failures. Sampling confirmed it, and then the practical answer was to measure all 120, because a reveal takes about ninety seconds on a hung cabinet and a re-hung or replaced door takes rather longer.

What the specification should have said

Six lines. None of them costs anything to write, and each one moves the check from a part that can be verified in isolation to a result that somebody who was not there has to be able to repeat.

• State the reveal on the hung cabinet, with a method. Reveal between adjacent doors shall be 3.0 mm +0.5/-0, measured on the assembled cabinet with the doors closed, at 100 mm from the top edge, at mid height and at 100 mm from the bottom edge of each internal joint, using a wedge gauge reading to 0.1 mm. Every reading shall be inside the band, and the spread of readings down one joint shall not exceed 1.0 mm.
• Name the hinge and the drilling distance, and keep the overlay decision with the buyer. Concealed hinges shall be clip-on, 110 degree, full overlay, 35 mm cup, 45 mm screw spacing, soft close, two per door. The cup hole shall be bored with its edge 4.0 mm from the door edge, giving a cup centre 21.5 mm from the hinge edge. Where the order does not name the model, the buyer approves the drilling distance in writing before any door is bored.
• Close the remaining door-side numbers, because they are what the cups are actually measured against. Cup hole 35.0 +0.1/-0 mm diameter by 13 mm deep, fixing hole 11.5 mm deep, fixing holes 45 mm apart, cup centre 76.2 mm from each end of the door to the cup centre, leaf 18 mm, which leaves 5 mm of material ahead of the cup and not less.
• Keep the 32 mm system as the carcase reference, and say what it governs. Side panels and dividers shall carry 5 mm system holes at 32 mm centres with the first row 37 mm from the front edge, for hinge mounting plates, shelf supports and drawer runners. The 32 mm grid sets the height of the hinge, not the reveal; the reveal is set on the door side, and any change to the carcase hole pattern needs written approval before drilling.
• Make the reveal a hold point on the factory's own check sheet. The reveal shall be measured and recorded on every cabinet before packing, at the three positions in the first clause, and the record travels with the order. The first ten cabinets of the run shall be offered for inspection before the remaining doors are bored.
• Write down that part conformity is not assembly conformity. Conformity of the hinge, the cup hole, the jig setting and the carcase hole pattern does not constitute conformity of the reveal. The reveal is a separate acceptance characteristic, measured on the hung cabinet, and a cabinet conforms only when both the parts and the reveal conform.