Is a thicker wall always better on a Long Weapon Case?

Answer: No. Thickness buys weight; stiffness also depends on rib height and span. A millimetre costs a quarter of the mass, a taller rib far less.

Why not subtract twice the wall from the outside size?

Answer: Rib roots, bumper returns and draft angle sit in between, adding four to nine millimetres. Measure the Long Weapon Case cavity from its supporting faces.

Is 180 mm a fixed rib pitch?

Answer: A starting value. Under 300 mm wide you can open to 220 mm, over 500 mm tighten to 160 mm; the test is sag under load.

What changes above 20 kg?

Answer: The structure, not the thickness: five latches, rib height at 2.4 times the wall, two base spines, usually wheels.

Long Weapon Case Specs: 14 kg Load, 5 mm Wall, 3 Ribs

Quick answer: A Long Weapon Case spec is a chain: load sets the cavity, the cavity sets the wall, deflection sets the ribs. Skip a link and you pay in kilos.

Load and cavity size come first
Wall thickness follows deflection, not habit
Ribs break the long span at 180 mm
Seals, latches and four tolerances
Five hard lines to put on the drawing
FAQ

1. Load and cavity size come first

A Long Weapon Case spec is a chain, not a grid: load sets the section, the section the wall, the wall the rib pitch and latch count.

Start with design load: weigh equipment, liner, fittings and straps, then add twenty per cent. Mid-size cases land between twelve and sixteen kilograms; past twenty kilos you need a different structure. Set the cavity between the furthest supporting faces, never the outside shell: wall, rib roots and bumper returns add four to nine millimetres. Stiffness rises with the cube of thickness, so a doubled load never doubles the wall.

Design load	Wall	Rib height	Latches	Cavity length
up to 8 kg	3.5 mm	8 mm	3	under 700 mm
8 to 16 kg	5 mm	12 mm	4	700 to 1200 mm
16 to 26 kg	6.5 mm	16 mm	5	1200 to 1600 mm

2. Wall thickness follows deflection, not habit

Set allowed deflection and work backwards. One five-hundredth of the span is standard: a one-metre span may sag two millimetres before the seal opens.

Leave process margin: walls vary by plus or minus 0.4 mm, so a 5 mm callout passes at 4.6 to 5.4 mm, and the stiffness check uses 4.6.

Long Weapon Case: grey closed hard case on an airport roller conveyor, two side latches and moulded handle facing out, scuffed corners, terminal windows behind

Temperature belongs in the same chain. At minus 30 °C polyethylene stiffens and loses toughness; at plus 65 °C it softens and creeps, which never springs back. Add 0.5 mm to the lid.

3. Ribs break the long span at 180 mm

Long cases fail on span, not wall: a flat panel crossing 1.2 m sags over four times as far as a short one under load.

Rib height at 1.8 to 2.4 times the wall: lower stops resisting bending, higher tears on ejection
R3 fillets at the root, since R2 concentrates stress where a drop test starts a crack
No rib directly behind a latch, or the seal lifts instead of closing
Remove 0.3 mm where cross ribs meet longitudinal ones, or shrink leaves a sink mark
Stop ribs 6 mm short of the end wall for thermal growth

Dense ribs cannot rescue a wrong cavity: ten spare millimetres and they protect nothing.

4. Seals, latches and four tolerances

A gasket works on compression, not adhesive. Target twenty-five per cent squeeze: under twenty it will not return, over thirty it takes a set. The groove runs 0.8 mm wider than the section.

Long Weapon Case: near-black hard case on a table, two front draw latches, one moulded handle, rounded corner bumpers, camera and two lenses at right

Item	Target	Tolerance	What goes wrong
Gasket squeeze	25%	plus or minus 5 points	slow return, dust ingress
Latch pitch	400 mm max	plus 20 mm	lid flexes in transit
Lid to base offset	1.5 mm	plus 0.5 mm	two hands to close
Hinge axial play	0.3 mm	plus or minus 0.2 mm	stiff action, worn pin

Latch count follows span, not length. Past 400 mm of unsupported lid the panel pumps and the gasket separates, so the case seems to leak water when it leaks air. Draw latches need 2 mm of take-up to bite.

5. Five hard lines to put on the drawing

Reinforced on a drawing leaves the toolroom guessing.

One: dimension the cavity from supporting faces, shell figure in brackets. Two: give the wall as nominal plus tolerance band and name nine measuring points, mid side, 100 mm from each end, rib root. Three: state rib height, pitch and fillet radius together.

Four: dimension latch and hinge holes from a common datum, since error compounds along a long case. Five: keep groove width, depth and squeeze on one line. Hit all five and the first sample fits.

Conclusion

A Long Weapon Case spec holds up when the load carries a factor, the cavity is measured from supporting faces, the wall comes from deflection and hot-case creep, and the rib pitch cuts the span. Each of those four closes off a revision on a Long Weapon Case programme.

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.