How much clearance should a medical case cavity allow?

Answer: One to two millimetres per side for fingers, 20 mm for wall and ribs. Separate budgets: mixing them grows the case and shrinks the cavity.

Does a thicker wall make a medical case more drop resistant?

Answer: No. Past 3.5 mm the benefit falls away while weight and sink risk climb. Resistance comes from double-wall corners: 3.0 mm with an 8 mm radius outlasts a 4.5 mm flat wall.

Which load figure should be printed on a medical case?

Answer: Three: 22 kg static, 150 kg across four stacked cases, a 1.2 m drop. One total says nothing about stacking.

Why is the envelope tolerance looser than the cavity tolerance?

Answer: The envelope drives packaging and mounts, where ±2.0 mm is enough; the cavity decides fit, so it holds ±1.5 mm.

Can a medical case specification change after the tool is cut?

Answer: Only with a version number. Every 5 mm of envelope change redraws the foam die and carton.

Medical Case Specifications: Size, Wall Thickness and Load

Quick answer: A medical case is specified from the inside out: fix the largest instrument and finger clearance first, add wall and rib depth to reach the envelope, then size wall thickness and machine tonnage against load and drop.

Sizing a medical case from the inside out
Wall thickness and ribs: stiffness comes from section shape
Three load cases: static, stacked and drop
Handles, hinges and latches: the force ratings
Turning specs into drawing language: tolerance and acceptance
FAQ

1. Sizing a medical case from the inside out

A medical case specification that starts with the envelope comes back for rework. Work backwards: list the largest item that must fit, then ask whether fingers reach past it, whether the lid presses, whether a divider fits above. Those answers give the cavity, and wall plus lid depth give the envelope.

An internal 440×310×160 mm means a 480×350×190 mm envelope: 20 mm per side covers 3.0 mm of wall, 12 mm of rib depth and 5 mm of rim engagement. Empty weight is near 3.6 kg; past 4 kg it needs a strap.

Item	Value	Decided by
Cavity	440×310×160 mm	largest item plus clearance
Wall	3.0 mm	load and drop
Envelope	480×350×190 mm	cavity plus wall, lid

2. Wall thickness and ribs: stiffness comes from section shape

3.0 mm is the usual starting point: melt reaches the far end of the mould, a drop does not crack it, and it still carries by hand. Thickness alone does not set stiffness. A flat 3.0 mm panel bows under 22 kg, while the same panel with two ribs 12 mm deep barely moves.

Medical Case: moulded handle with a through-hole on the yellow lid, thickened at the root, with a rib and parting line along the edge

Three rules govern ribs: depth under four times the wall or the root sinks, root thickness at 0.6 of the wall to avoid read-through, pitch within 60 mm. Sections differing by over 0.3 mm cool unevenly and warp.

3. Three load cases: static, stacked and drop

Load is not one number. Static is 22 kg on a shelf for 24 hours. Stacked is four cases high, the bottom taking 150 kg on the lid. Drop is 1.2 m onto corners, edges and faces, corner first.

Case	Condition	Pass criterion
Static	22 kg, 24 h	deflection under 2 mm
Stacked	four high, 150 kg, 7 days	no permanent set
Drop	1.2 m, six faces three points	no crack, latches shut

Each case loads a different feature, so one body passes only by dividing work.

4. Handles, hinges and latches: the force ratings

The handle carries the concentrated load, so it gets two figures. Static is three times rated: 22 kg of contents means 66 kg pulled for a minute without separation. Dynamic is one times, at walking gait, ten thousand cycles. Static tests ultimate strength, dynamic tests fatigue.

Medical Case: yellow case open with a grey generator, a red fuel can, a coiled cable and wrenches resting on foam inside

Hinges are specified by pin diameter and bearing length: a 4 mm pin with 60 mm per side suits a hand-carried case; longer bodies need a third support or the lid bows. Latches take a holding force and 30 to 60 N of opening force, light enough for gloves.

5. Turning specs into drawing language: tolerance and acceptance

A specification table must be inspectable, or it is a description: envelope with tolerance, wall and rib positions, warp, gap at the mating faces.

Shrinkage belongs on the drawing: polypropylene moulds at 0.5 percent, so 480 mm needs 2.4 mm of compensation or the first shot is undersize. Tonnage too: at 35 MPa over the projected area, a 480×350 mm case needs 600 to 800 tonnes, below which flash appears at the parting line.

Check	Specification	Out of tolerance
Envelope	480×350×190 mm, ±2.0 mm	rework tool or downgrade
Wall	3.0 mm, ±0.15 mm	adjust process
Warp and gap	0.6 mm and 0.4 mm max	straighten, scrap or fit
Latch opening	30 to 60 N	reset latch position

Conclusion

A medical case specification is numbers constraining each other: cavity sets envelope, envelope sets tonnage, load sets wall and ribs, tolerance decides whether it can be inspected. Put the four on one sheet and it stops being a guess; widen one alone and the price is paid in weight, cost or yield.

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.