Why not quote the equipment envelope as the cavity?

Answer: Clamp clearance, hand room and ribs sit between them, leaving no room for foam.

How is 3.0 mm wall justified on an Equipment Protection Case?

Answer: Payload times drop height: 18 kg at 1.2 m needs 3.0 mm, double the payload 4.0 mm.

Do more latches seal better?

Answer: No. Four at 240 mm compress a 3 mm gasket; six leave slack travel.

Should stack height appear on the spec sheet?

Answer: Yes. Four high and eight high are different lid structures.

What does ±0.5 mm on the cavity mean in assembly?

Answer: A 1 mm band in foam compression, so groove depth and latch travel must match.

What is the minimum inspection list for an Equipment Protection Case?

Answer: Cavity, warp, salt spray, drop and thermal cycling; omit one and a failure mode is undecidable.

Four Numbers Behind an Equipment Protection Case Spec

Quick answer: An Equipment Protection Case spec comes from four inputs: payload, drop height, stack height and temperature. They fix the cavity, the cavity plus wall fixes the envelope, the perimeter the latch count.

Four inputs behind an Equipment Protection Case spec
The cavity dimension chain, link by link
Wall thickness and ribs from drop energy
Latch count and hinge span by perimeter
Turning the spec into a drawing
FAQ

1. Four inputs behind an Equipment Protection Case spec

An Equipment Protection Case is not drawn first and filled later. Payload, drop height, stack height and temperature are inputs; the envelope is an output.

Input	Example	What it sets
Payload	18 kg	Wall thickness, rib height
Drop height	1.2 m	Bumper thickness, foam clearance
Stack height	4 high	Lid flatness, pad width
Temperature	-20 to 55 °C	Resin grade, gasket hardness

Temperature is the input people forget. Polypropylene loses about 60 percent of its notched impact at -20 °C, so another grade behaves like another product. Silicone flexes at -40 °C while neoprene stiffens near -20 °C, and at 55 °C a loaded side wall creeps inward within a year.

2. The cavity dimension chain, link by link

The dimensions of an Equipment Protection Case form a chain, and each link needs a stated basis.

Link	Example	Basis
Equipment envelope	420 × 300 × 150 mm	Measured outline, with connectors
Clamp and hand clearance	20 mm per side	Lifting, cabling, fingers
Cavity net size	460 × 330 × 170 mm	Sum, rounded
Outside envelope	480 × 350 × 190 mm	Cavity plus 3.0 mm wall and 8 mm rib

Equipment Protection Case: olive green case on a lower rack shelf, four lid latches closed, handle facing out, scuffed wall above a rusted tray

Cavity figures are quoted at the narrowest point, never at the opening, and corners carry an R8 radius.

The chain ends at the stacking face: four cases at 18 kg load the bottom unit with 72 kg, yet its lid centre collapses. Ribs there are spaced closer, not thicker.

3. Wall thickness and ribs from drop energy

Wall thickness on an Equipment Protection Case is back-calculated from drop energy: 18 kg at 1.2 m arrives with about 212 J, absorbed in milliseconds by bumpers, wall and foam.

Main wall 3.0 mm; below 2.5 mm the keeper root cracks first.
Ribs 8 mm high on a 120 mm pitch; each extra 2 mm adds 30 percent section modulus.
Rib roots at R1.5, because a square transition tears on impact.
Bumpers 6 mm, separate, so a knock swaps a corner.
Feet 12 mm high, 30 × 40 mm patch.

Stiffness is not the goal. A wall too rigid returns the impact into the equipment.

4. Latch count and hinge span by perimeter

Latches on an Equipment Protection Case are spread by perimeter: a 480 × 350 mm body measures 1660 mm, two on the long side at 240 mm and one per short side.

Equipment Protection Case: open olive green case on a metal table, foam cavities in the lid, egg-crate foam at right, vacuum pouches inside

Each latch clamps at 60 to 90 N, about 150 N per metre, pressing a 3 mm gasket to 2.1 mm.

Parameter	Value	Basis
Latch count	4	One per 300 mm of perimeter
Latch spacing	240 mm	No wavy gasket impression
Hinge span	320 mm	Past 400 mm the lid lifts
Screw torque	2.5 N·m	No stripping or cracks

Six latches at 160 mm load the first three and leave the rest slack; a 400 mm span sags the lid 0.4 mm.

5. Turning the spec into a drawing

The specification of an Equipment Protection Case ends as drawing numbers in a fixed order: cavity, envelope, holes, material, inspection. Reverse it and tolerances never recover.

The 460 mm cavity carries ±0.5 mm, the 480 mm envelope ±0.8 mm, warp inside 1.0 mm per metre. The gasket groove is 0.2 mm wider than the strip and 0.6 mm shallower, placing compression at 25 to 30 percent.

Inspection item	Value	Method
Cavity size	460 × 330 × 170 mm, ±0.5	CMM or gauge
Lid warp	1.0 mm per metre	Plate and feeler
Salt spray	480 h, no perforation	Spray cabinet
Drop	1.2 m per face	Loaded production drop
Thermal cycling	-20 to 55 °C, 5 cycles	Climatic chamber

Conclusion

An Equipment Protection Case spec is one chain from four inputs: payload and drop set structure, stack height and temperature set material, cavity plus wall gives the envelope. Run the chain and the specification of an Equipment Protection Case stops depending on trial fitting.

This article discusses only the container (case body) side of specifications and design intent, and does not cover any handling, loading or use of the contents.