How do I get a tool bag cavity from the envelope?

Answer: Subtract two walls, two draft allowances and two liners: 460 × 360 × 220 mm with 3.0 mm walls and 15 mm foam leaves 421.6 × 321.6 × 181.6 mm.

Is a 3.0 mm wall enough?

Answer: For shop handling, yes. At 25 kg and a 1.2 m drop, corners below 2.6 mm whiten, so base and mounts go to 3.4 mm locally.

How is handle hardware calculated?

Answer: Rated load times 4, then pin section against allowable shear. Two φ8 pins give 804 N against 980 N; two φ10 pins reach 1 256 N.

Why not spread tolerance evenly?

Answer: Cavity governs assembly, envelope governs layout, the joint governs sealing, so each tightens differently.

What is the minimum spec sheet?

Answer: Seven fields: envelope, cavity, wall and ribs, load, handle hardware, sealing, tolerances and gauges.

Tool Bag Specifications: Dimensions, Wall Thickness and Load

Quick answer: A tool bag specification is three chains that must agree: the dimension chain from envelope to cavity, wall and ribs that set stiffness, and rated load that works back into handle hardware.

Where a Tool Bag Specification Starts: The Dimension Chain
Wall Thickness and Material Build
Working Back From Load to the Handle
Tolerances and the Gauges That Check Them
Writing the Spec Sheet Without Mismatches
FAQ

1. Where a Tool Bag Specification Starts: The Dimension Chain

A tool bag specification grows outward from the cavity. On a 460 × 360 × 220 mm body with 3.0 mm walls and 1.2 mm draft, the cavity reads 451.6 × 351.6 × 211.6 mm, and volume falls from 36.4 L to 33.6 L.

Link	Value	Note
Envelope	460 × 360 × 220 mm	Maximum outline
Single wall	3.0 mm	Nominal shell
Draft	1.2 mm	Per side
Cavity	451.6 × 351.6 × 211.6 mm	Envelope less walls
Usable space	421.6 × 321.6 × 181.6 mm	Cavity less liners

Two 15 mm foam layers take 30 mm more; four 50 mm casters lift the body to 285 mm, past a 300 mm shelf pitch.

2. Wall Thickness and Material Build

Thicker is not better. A 2.6 mm shell whitens at the corners after a 1.2 m drop, 3.0 mm is the working grade, and 3.4 mm belongs at the base. Each extra 0.4 mm adds 13 percent weight and 8 s of cooling, moving the cycle from 62 s to 70 s.

Tool Bag: red hard case standing open on a dark backdrop, black foam compartments inside, two front latches, a round lock and corner ribs

Ribs beat thickness. At 1.8 mm thick, 9 mm high and 55 mm pitch, section modulus rises 2.4 times for 6 percent more weight. Polypropylene with 20 percent talc shrinks 1.5 percent; 10 percent glass fibre lifts modulus from 1 500 to 2 300 MPa but drops notched impact to 6 kJ/m².

3. Working Back From Load to the Handle

Rated load comes first. A 25 kg tool bag at a safety factor of 4 gives 980 N. A φ8 mm pin at each end offers 50.3 mm²; at 8 MPa each carries 402 N, so the pair gives 804 N and falls 176 N short. At φ10 mm the pair reaches 1 256 N.

Check	Expression	Result
Design load	25 kg × 4	980 N
Two φ8 pins	50.3 mm² × 8 MPa × 2	804 N, short
Two φ10 pins	78.5 mm² × 8 MPa × 2	1 256 N, passes
Stacking	3 × 18 kg	54 kg

The handle also bends: a 45 mm grip offset turns 25 kg into 11 N·m, or 18 MPa at a 3.0 mm root, which a 2 mm boss ring halves.

4. Tolerances and the Gauges That Check Them

Cavity takes ±1.0 mm, envelope ±1.5 mm, the lid joint ±0.5 mm and flatness 0.6 mm, because a 0.3 mm spread between cavities is ordinary shrinkage. A 0.02 mm caliper reads the envelope, a coordinate machine reads 8 points per unit, and a plug gauge 2 mm under nominal rejects an oversize cavity in 15 s.

Tool Bag: red hard case at an angle, lid half open showing black foam with cut-outs, one-piece top handle, metal latch and corner ribs

Gauge repeatability stays under 10 percent. Wall thickness comes from 5 ultrasonic points 80 mm apart, since rib roots read 2.4 mm rather than the nominal 3.0 mm.

5. Writing the Spec Sheet Without Mismatches

Seven fields carry a tool bag spec sheet: envelope, cavity, wall and ribs, rated load, handle hardware, sealing, tolerances and gauges.

Field	Sound wording	Common error	Consequence
Cavity	451.6 × 351.6 × 211.6 mm	Envelope only	Liner will not seat
Wall	3.0 mm ±0.2 mm, ribs 1.8 mm	About 3 mm	Quoted at 2.6 mm
Load	25 kg vertical lift, factor 4	25 kg alone	Handle sized at 1.5×
Tolerance	Cavity ±1.0 mm, flatness 0.6 mm	Per national standard	Two rulers

The commonest error quotes the envelope as a cavity; the second writes about 3 mm, so the shop plans 2.6 mm and ships 90 g light. The third omits load direction, doubling the moment in a sideways drag.

Conclusion

The dimension chain turns an envelope into a cavity, wall and ribs put stiffness where load arrives, and the load calculation settles the hardware. Ten millimetres lost in the cavity is repaid later. A tool bag derived from its dimension chain is the one whose quotation matches the sample.

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.