What sets the wall thickness of a Hand Carry Hard Case?

Answer: The load path. Sides answer squeeze at 3.2 mm, the base span at 4.5 mm, the rim preload at 5 mm.

Why can the cavity not match the load exactly?

Answer: Three allowances: 3 mm clearance per side, 15 to 20 mm of cushion, 4 mm of rib intrusion.

Do more ribs make a Hand Carry Hard Case stronger?

Answer: No. Pitch under 60 mm short-shots, and thick ribs sink at the root.

How many latches does a Hand Carry Hard Case need?

Answer: One per 240 mm of rim, so five on a 1.2 m perimeter; three leaves 0.6 mm.

Case Weight Is the Wrong Start for Hand Carry Hard Case Specs

Quick answer: A Hand Carry Hard Case is not specified from total weight. Set the cavity first, derive wall thickness from support points and span, then add ribs. For an 18 kg load, 3.2 mm sides, a 4.5 mm base and a 5 mm rim are enough; 6 mm everywhere only adds mass.

Case Weight Is the Wrong Starting Point
Cavity Size Derived Backwards from the Load
Wall Thickness Follows the Load Path
Rib Pitch and Corner Radius Make Stiffness
Gasket, Latch and Handle Sizes Move Together
Turning the Chain into a Spec Sheet
FAQ

1. Case Weight Is the Wrong Starting Point

Buyers ask how thick the wall should be for 20 kg. Weight sets handle and hinge size, not thickness.

An 18 kg case may load a 200 mm square, a 12 kg case spreads it, so equal walls dent the lighter one first.

Common claim	What happens	What to measure
20 kg needs 5 mm	base collapses	support spacing
thicker is stronger	40 percent more mass	wall to rib ratio
size by outside dimensions	load will not fit	cavity, radii

Weight is an output, not an input.

2. Cavity Size Derived Backwards from the Load

A Hand Carry Hard Case cavity equals load envelope plus clearance, cushion and rib intrusion.

Hand Carry Hard Case: open navy case with a foam-lined lid on a wooden bench, cables, gloves, a notebook and pouches laid out, shelving behind

Clearance is 3 mm per side; a tight gap becomes levering.

Cushion follows drop height: at 1.2 m, EPE needs 15 mm, EVA 20 mm.

A 4 mm rib takes 8 mm off usable width; thinner walls carry deeper ribs.

3. Wall Thickness Follows the Load Path

Walls on the handle, latch and support routes run thickest.

Hand Carry Hard Case: closed navy case on an airport baggage conveyor, two latches and a folding handle facing out, pale windows behind

Zone	Load	Thickness	Basis
Side	squeeze	3.2 mm	30 kg stacked
Base	support	4.5 mm	0.8 mm sag
Rim	preload	5 mm	bending, groove
Handle root	lifting	6 mm	bolt creep

At 3.2 mm the side wall sits at its floor; thinner, the melt front freezes into a weak weld.

The base spans: 30 kg at 200 mm spacing sags 0.8 mm, and at 300 mm the feet lift.

The rim resists preload and carries a 4 mm wide, 5 mm deep groove; a wall under 3 mm flares out. The lid is sized by stacking: the bottom of three carries 80 kg, sag inside 1.5 mm. The handle root follows the M6 bolt, whose 9 kN clamp creeps any plastic face under 250 square millimetres. Each number answers one failure mode. Write the test beside each number. Without it, the moulder works to nominal values.

4. Rib Pitch and Corner Radius Make Stiffness

Ribs close the stiffness gap, and efficiency depends on pitch, not height.

Height 3x wall: beyond it the root sinks.
Thickness 0.6x wall: equal to the wall it hot-spots.
Outside radius R8: below it, corners crack first.
Draft 1 degree: taller ribs need more.

Past 80 mm the panel sinks about 0.5 mm, which the eye catches.

Radius matters more in a drop: R8 spreads impact over 60 mm, R3 over 20 mm, tripling stress at -10 °C.

5. Gasket, Latch and Handle Sizes Move Together

Fitting positions follow from shell dimensions and feed back into them.

Latches run every 240 mm of rim: five on a 1.2 m perimeter holds the gap at 0.15 mm, three leaves 0.6 mm.

Gasket squeeze sits at 28%: under 25 it leaks, over 35 it cannot rebound.

Handle span stays at 160 mm or less; beyond it the root needs an insert and cost rises 12 percent.

6. Turning the Chain into a Spec Sheet

Parameter	Value	Tolerance	Check
Cavity	envelope + 6 mm + cushion	+2 / 0 mm	caliper
Side wall	3.2 mm	±0.15 mm	ultrasonic
Base	4.5 mm	±0.2 mm	ultrasonic
Rim	5 mm	±0.1 mm	caliper
Rib pitch	60 mm	±3 mm	drawing
Latch spacing	240 mm	±5 mm	tape
Gasket squeeze	28%	±3%	feeler

A 0.15 mm wall spread moves mass 4 percent and stiffness 8 percent.

Specify a Hand Carry Hard Case for the toolmaker, not the buyer.

Put the derivation in the agreement: with results only the moulder adjusts by experience, with reasons changes come back.

Conclusion

A Hand Carry Hard Case is a chain: cavity sets size, load sets thickness, pitch sets stiffness, fittings set the rim. An 18 kg unit runs 3.2 mm sides, a 4.5 mm base, 60 mm pitch and 240 mm latch spacing; change one, recheck three. That is how a Hand Carry Hard Case survives its first drop.

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.