Can the cavity of a Rolling Tool Case be scaled from the outline?

No. The load list fixes the cavity and the outline follows it. Scaling breaks the cavity first, then the structure, then the wheel positions.

Is 2.6 mm always too thin?

It depends on gross weight. Under 25 kg with trips of 300 m, 2.6 mm plus local ribs holds; above 35 kg the base goes to 3.2 mm with inserts.

Does tightening tolerances cut warranty claims?

Only two bands repay it: parting-line flatness and rail hole position. The rest add rework hours without a visible drop in claims.

Why is a small batch so much dearer?

Tooling. A 280,000 yuan mould is 140 yuan a case at 2000 units and 46.7 at 6000. At low volume, change structure, use a shared mould or drop the surface finish.

How do you prove a thinner wall still works?

35 kg static load for 30 days, a 1.2 m six-face drop, and 500 lid closures for latch fatigue. Pass all three, then discuss cost.

How much of the quote is structure?

At this size, the moulded body is 40%, wheels and trolley 25%, hardware and seals 15%, assembly and packing 20%.

Rolling Tool Case Specs: 11 Yuan Saved, 21 Yuan Lost

Quick answer: A Rolling Tool Case is specified backwards from the load list: contents fix the cavity, cavity and gross weight fix wall thickness, thickness fixes ribs and wheel mounts. Each step carries a price, from material saved to rework hours and tooling per unit. Put the three costs on one sheet and the specification has one answer.

Cavity Size Derived from the Load List
What 0.6 mm of Wall Buys and Costs
Load Paths from Mount to Rail
Tolerance Bands and Assembly Rework
Tooling Amortisation and the Batch Break Point
FAQ

1. Cavity Size Derived from the Load List

Start with the list of what goes in, not with an outline. A longest item of 480 mm, a tallest of 210 mm, 12 kg at the heaviest and two stacking layers fix the numbers. Two 12 mm foam walls and an 8 mm divider give 520 mm of length; two layers with divider and base pad give 240 mm of height; three pieces at 96 mm plus foam give 310 mm of width. Only then does the outside become a discussion.

Everything outside the cavity serves it: wall, ribs, mounts. The derivation runs cavity, outline, structure, running gear. Reverse it and the load no longer fits, or the walls end up like paper.

Input	This case	Derived	Cost of overshooting
Longest item	480 mm	Cavity 520 mm	Foam crushed on removal
Two layers	210 mm each	Height 240 mm	Lid will not seat
Three across	96 mm each	Width 310 mm	Divider bows
Gross weight	35 kg	Wall 3.2 mm	Base sags, mount whitens
Trip length	300 m	Wheel 75 mm	Tread flats

A 520 × 310 × 240 mm cavity at 35 kg is the dividing line. Under 25 kg allows 2.6 mm walls with local ribs; above 35 kg needs 3.2 mm and a moulded insert at each mount. That 10 kg band decides every cost line below.

2. What 0.6 mm of Wall Buys and Costs

Going from 3.2 mm to 2.6 mm takes part weight from 5.0 kg to 4.2 kg. At 14 yuan a kilo of modified ABS, that is 11.2 yuan saved per case, which looks free until the 0.6 mm is paid back.

The first bill is flatness. Thinner walls cool unevenly, so lid flatness moves from 0.8 mm to 1.6 mm, the middle meets first, the corners stay open and the seal never compresses. The second is creep: 35 kg on a 2.6 mm base sinks 1.2 mm in 30 days, and the mounts tilt with it. The third is scrap, up from 1.4% to 5.2%, whose extra 3.8 points add 4.5 yuan per good unit at 120 yuan each.

Rework is the big one. A flatness failure goes onto a jig for 22 minutes at 45 yuan an hour, or 16.5 yuan. Save 11.2, pay 21, and every case loses about 10 yuan.

3. Load Paths from Mount to Rail

A Rolling Tool Case carries load along three paths, and the specification exists to keep all three unbroken.

Vertical: cavity floor to side wall, wall to lower edge, then into the mounts. Floor ribs run into the wall at 8 mm minimum.
Diagonal pull: rail into back panel, back panel into both side walls, on a 3 mm backing plate with bolts no wider than 80 mm apart.
Carrying: handle into lid, lid into the short ends. Handle blocks wrap the lid edge rather than sit on it.
Junctions are weakest: mount to wall, rail to back panel, handle to lid, each 4.5 mm locally.
Fasteners close the chain: M6 studs at 6 N·m through a metal insert, never straight into plastic.

Get the three paths right and strength stops being a matter of adding material.

4. Tolerance Bands and Assembly Rework

Tolerance is not a virtue; every tightened band adds an operation. Five dimensions matter on a Rolling Tool Case and the rest can stay loose.

Rolling Tool Case: a red case standing in a plant, four steel castors beneath, grid ribs on the lower body, two latches, an orange strap

Feature	Band	If it drifts	Rework
Parting-line flatness	0.8 mm	Seal never seats	22 min
Lid-to-base gap	0.3 mm	Latch loose or blocked	12 min
Mount parallelism	0.5 mm	Wheels uneven, case pulls	18 min
Rail hole position	±0.2 mm	Trolley will not fit	25 min
Latch anchor height	±0.3 mm	Weak closing force	8 min

Two of the five carry the money: flatness at the parting line for sealing, hole position at the rail for assembly. The rest can sit at ±0.5 mm without complaint.

5. Tooling Amortisation and the Batch Break Point

A mould for a Rolling Tool Case costs about 280,000 yuan. At 6000 units it adds 46.7 yuan per case; at 2000 units, 140 yuan. Same structure, 93 yuan apart, which is why small runs cannot copy the specification of a volume order.

Rolling Tool Case: a blue case open on a wooden bench, grey foam bays holding green circuit boards and coiled cable, a dial gauge nearby

Cycle time counts too: 3.2 mm walls cool for about 210 seconds against 175 seconds at 2.6 mm, two hundred parts a day on one machine. Shorten the cycle and scrap rises, and the bill returns to the section above.

The break point sits near 3000 units. Below it, tooling takes over a third of unit cost and the material saving is noise; above it, wall and structure show in the quote. Ask which side a batch falls on before negotiating price.

Conclusion

The specification of a Rolling Tool Case is a chain that can be costed to the end: load list to cavity, cavity and weight to wall thickness, thickness to ribs and mounts, tolerance budget spent on two features, tooling spread across the batch. Every link converts into money, so where the saving sits and where the loss lands are visible on one page. Walk the chain first, and a Rolling Tool Case is never specified by saving 11 yuan to lose 21.

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.