What wall does Protective Case Sales normally quote?

Answer: 2.2 mm at 12 kg, 3.4 mm at 38 kg, 4.2 mm at 75 kg — driven by span and rib pitch.

Can the cavity just follow the instrument outline?

Answer: No. Allow 15 mm of foam: 1210 mm of gear needs 1240 mm, or impact reaches the instrument.

Does a tighter rib pitch always stiffen more?

Answer: Past 160 mm the return falls away: 160 mm to 120 mm removes 15% more deflection for 5% weight.

How is the ±0.15 mm wall checked?

Answer: Ultrasonic gauge, 8 floor points and 3 per side wall, kept 10 mm clear of rib roots; two bad points reject it.

How many latches are needed?

Answer: One per 350 mm of rim, a rule that holds across Protective Case Sales sizes: four on the long side, one at each end.

Why must mould ownership be on the quotation?

Answer: USD 29,000 over 3 years is paid twice if ownership is unclear, so Protective Case Sales contracts name the buyer as owner with transfer rights.

1240 mm Cavity: How Thick Should Protective Case Sales Go?

Quick answer: Thickness is an output, not an input. Take 38 kg, apply a 3× factor for 114 kg, run the 1240 mm span, and 3.4 mm at 160 mm rib pitch lands at 1.2 mm deflection. Rim flatness of 0.6 mm, ten latches and 7.5 N·m follow from the same chain.

Load and cavity come first
Back-calculating wall from bending
Ribs and lid: three load paths
Gasket, latches and hinges
Five lines on the drawing
FAQ

1. Load and cavity come first

The order cannot be reversed: payload and cavity first, wall second, ribs and latches last. Pick a sturdy-looking wall and the shell overshoots.

Protective Case Sales enquiries quote the nameplate weight; the dynamic figure bends the floor. A 38 kg instrument becomes 114 kg at 3× over 1240 × 480 mm; what tests it is a point load.

Cavity is the instrument plus 15 mm of foam: 1210 mm of gear gets 1240 mm, a 450 mm width 480 mm. Too much and the case grows heavy, too little and the foam bottoms out.

Payload	Cavity	Target weight	Wall	Floor
12 kg	620 mm	3.6 kg	2.2 mm	Flat
38 kg	1240 mm	6.4 kg	3.4 mm	Grid ribs
75 kg	1600 mm	12.8 kg	4.2 mm	Double ribs, inserts

Foam at 25 kg/m³ adds 1.8 kg: it carries nothing but it ships, and Protective Case Sales figures that skip it return as a weight complaint.

2. Back-calculating wall from bending

The floor is a simply supported beam: 1240 mm span, 114 kg uniform load, moment as load times span squared over 8. At 3.4 mm and 160 mm pitch, deflection is 1.2 mm — a thousandth of the span.

Protective Case Sales: a green case on white, bridge handle joined to the lid edge, three rib groups at each corner, ribbed feet

Wall	Rib pitch	Weight	Deflection	Use
2.6 mm	200 mm	5.1 kg	2.4 mm	Light gear
3.4 mm	160 mm	6.4 kg	1.2 mm	General transport
4.2 mm	140 mm	8.9 kg	0.7 mm	Long haul

The trade is weight and cost, not strength: 0.4 mm more costs 7% weight and 8% unit cost for 12% less deflection, while pitch from 200 mm to 160 mm costs 3% and removes 40%. Protective Case Sales buyers push for wall; the numbers say pitch first.

State tolerance separately: a 3.4 mm nominal moulds from 3.25 mm to 3.55 mm, so the sheet says ±0.15 mm and out-of-tolerance lots go back rather than being shimmed. PP at 1.6% shrinkage leaves a 1240 mm case 19.8 mm short, so the cavity is cut oversize.

3. Ribs and lid: three load paths

Ribs belong on load paths only: floor grid, corner posts, rim bead. Those three carry load from floor to wall to rim; ribs elsewhere are weight in every Protective Case Sales drawing.

Position	Form	Size	Job
Floor	Grid	10 mm high, 2.2 mm thick	Uniform load
Corners	Post	R2.5 root	Drop impact
Rim	Bead	12 mm wide	Flatness

The lid takes stack pressure and reverse impact, so its ribs run sparse and deep: 220 mm pitch at 12 mm.

Never delete the root radius, the first thing a Protective Case Sales sample review checks. R2.5 drops the stress factor from 2.6 to 1.4; without it a crack starts at the root. Draft at 1.5°, or ejection scuffs 0.1 mm off the wall where nobody looks.

4. Gasket, latches and hinges

Wall fixed, rim flatness fixed. Protective Case Sales drawings put a 1240 mm rim within 0.6 mm, or the gasket never seats.

Protective Case Sales: an ivory-white case on white, clean lid panel, bridge handle on top, two reinforced feet and a pale liner edge

Set the gasket at 26% compression: 11 mm cord closing to 8.1 mm in a 4.5 mm deep, 6 mm wide groove. Under 20% it leaks at the first uneven rim; over 32% it takes a set.

One latch per 350 mm of perimeter — four on the long side, one at each end, ten total. Drop one and that side opens under vibration while compression falls below 15%.

Three hinges, 6 mm pin, 0.3 mm clearance, 5 mm of local wall at the boss to survive 500 cycles. Inserts take 7.5 N·m with 2 mm of plastic around them.

5. Five lines on the drawing

Five lines carry the whole specification:

Line	Field	Example	Why it stands alone
1	Cavity	1240 × 480 × 300 mm	Locates foam
2	Wall, tolerance	3.4 ± 0.15 mm	Load path, weight
3	Rib pitch, height	160 mm, 10 mm	Deflection
4	Rim flatness	0.6 mm	Sealing
5	Latches, torque	10 pcs, 7.5 N·m	Vibration

Protective Case Sales quotations follow the same lines: mould USD 29,000 over 3 years, minimum 300 pcs, unit USD 40 with 8% scrap from the wall tolerance.

Conclusion

The chain leaves no room for adjectives: 38 kg becomes 114 kg, the 1240 mm span yields 3.4 mm at 160 mm pitch, and 0.6 mm of rim flatness carries 26% compression. Five lines and three tolerances make a specification measurable — the part of Protective Case Sales a competitor cannot copy.

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.