How much clearance should a Tool Kit Chest cavity leave?

Answer: 20 mm each end and side, 40 mm above. That is for fingers and foam, not machining; 60 mm oversize lets the load slide.

Is a thicker wall stronger?

Answer: No. A 3.2 mm wall with 2.0 mm ribs approaches a 4.5 mm panel at seventy percent of the weight, and thick walls add sink marks.

What floor thickness suits 30 kg?

Answer: 4.5 mm with four lengthwise ribs at 100 mm pitch. Deflection rises with load, and margin is cheaper than a rib added later.

Is ±0.8 mm tight enough for the cavity?

Answer: For foam, yes, since foam compresses about 1 mm. For a rigid tray dropping in, tighten to ±0.4 mm.

Must the sheet name gauges?

Answer: Yes. A tolerance without a gauge is a wish; naming the frame gives the mould shop a target.

Tool Kit Chest Specifications: Size, Wall and Load

Quick answer: A Tool Kit Chest specification closes like a chain: cavity, wall, outer size, pallet. Each link carries a tolerance and a gauge, so the drawing can be measured instead of argued about.

Building the Tool Kit Chest Dimension Chain
Allocating Wall Thickness
Back-Calculating Bottom Thickness from Load
Tolerances and Gauges
A Spec Sheet That Can Be Inspected
FAQ

1. Building the Tool Kit Chest Dimension Chain

A Tool Kit Chest specification is a chain, not a list of numbers. The cavity comes first: length from the longest item plus 20 mm at each end, width from the widest plus foam, depth from the tallest plus 40 mm of lid cushion.

With a 500 x 340 x 190 mm cavity, a 3.2 mm wall and 2.0 mm of rib relief give 510 x 350 mm outside, while 190 plus a 4.0 mm floor, a 60 mm lid and a 1.0 mm joint gap gives 258 mm high.

Chain link	Value	Source
Cavity	500 x 340 x 190 mm	460 mm item plus 20 mm each end
Outer	510 x 350 x 258 mm	Cavity plus wall, floor and lid
Pallet fit	4 per layer, 20 at five high	1200 x 800 mm pallet

At 560 mm long it still fits four per layer, but the pallet is wasted.

2. Allocating Wall Thickness

Tool Kit Chest: close-up of the orange folding handle, its twin reinforcing ribs, the moulded handle base and the lid parting line at the corner

One Tool Kit Chest carries six thicknesses: 3.2 mm main wall, 4.0 mm floor, 3.0 mm lid, 2.0 mm rib roots, 6.5 mm handle root, 6.0 mm hinge bosses.

Three rules govern the split. Adjacent walls stay within 1.5 times, or a 20 mm transition is needed. A rib root runs 0.6 times the wall, so 2.0 mm stays flat while 3.2 mm shadows the face. Every vertical face gets 1.5 degrees of draft, about 5 mm over 190 mm.

Polypropylene flows 200 times its wall, so 3.2 mm fills a 640 mm path. Thicker is not stronger: 4.5 mm adds forty percent in weight for under twenty percent in stiffness.

3. Back-Calculating Bottom Thickness from Load

Load is derived, not declared. A Tool Kit Chest carrying 28 kg in a four-high stack puts 84 kg on the lowest top face; over 0.17 square metres that is 4.9 kPa, and across a 340 mm span the L/200 limit is 1.7 mm.

A 4.0 mm floor deflects 1.5 mm and passes, while 3.2 mm gives 2.9 mm. Ribs beat thickness: three lengthwise and two across at 120 mm pitch cut the span to 120 mm, and deflection falls with the fourth power of span. The handle takes 28 kg times a 1.8 dynamic factor, so 50.4 kg at a 6.5 mm root.

4. Tolerances and Gauges

Tool Kit Chest: orange case open, black gasket round the lid, sockets and ratchet wrenches in die-cut black foam, front latch and folding handle

Tolerance follows function: the cavity mates with foam, so ±0.8 mm; the outer meets pallets, so ±1.2 mm; height ±1.5 mm; lid mismatch 0.3 mm or light escapes the gasket groove; floor flatness 0.6 mm.

Polypropylene shrinks about 1.6 percent, so the mould is cut 1.016 times nominal and corrected from the first shot. Three gauges cover the drawing: a go/no-go frame, where 500 x 340 mm enters and 1.6 mm oversize does not; an ultrasonic gauge at three points each on floor, wall and lid; a plate and indicator at four corners.

A no-go failure means recutting the cavity, not polishing it.

5. A Spec Sheet That Can Be Inspected

Three columns plus a gauge column beat prose, because purchasing, tooling and inspection then read the same table.

Item	Nominal	Tolerance	Gauge
Cavity	500 x 340 x 190 mm	±0.8 mm	Go/no-go frame
Outer	510 x 350 x 258 mm	±1.2 mm	Calipers
Wall	4.0 floor, 3.2 side	+0.3 mm	Ultrasonic, 9 points
Floor load	84 kg, 1 hour	1.7 mm maximum	Plate, indicator

The datum is what sheets forget: which face the 500 mm starts from, or whether thickness is read on a rib. Pin datum, gauge and frequency, and the Tool Kit Chest sheet becomes a decision rule.

Conclusion

Four steps close the chain: cavity from the load, outer size from cavity plus wall, floor and ribs from the stack, tolerances and gauges from the mating function. Skip one and the drawing returns at trial moulding. Put all four on a page and the size, wall and load of a Tool Kit Chest are finally fixed.

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.