Does 100 mm more instrument case depth really raise the tip angle?

Answer: Geometry says 39.8° to 48.0°, but a 50 mm forward shift returns it to 39.8°, and a centre rising from 180 to 240 mm pulls it down to 32.0°.

Which side should the ballast go on?

Answer: The opposite side to the offset. With the load forward, 1.5 kg at the rear drops the centre 16 mm and lifts the angle 1.8°; the same block at the front doubles the offset.

What centre height is safe for an 18 kg case?

Answer: At 300 mm depth, a centre within 180 mm gives 39.8°, while 240 mm leaves 32.0°. A 12° carry swing eats the same 12°, so below 20° of margin add ballast.

How much does offset grow under vibration?

Answer: A 50 mm offset at 0.5 g produces a 900 kg·mm moment, pallet slip rises from 8 to 12 mm, and one more strap is needed.

Instrument Case Depth and Centre of Gravity

Quick answer: Growing instrument case depth from 300 to 400 mm lifts the tip angle from 39.8° to 48.0°, yet a 50 mm forward shift of the load erases all of it. Centre of gravity height, not depth, decides stability.

Deeper is not steadier
Measuring the centre of gravity height
Fore and aft offset and ballast
Handle position against the base
Vibration and three impacts along the depth
FAQ

1. Deeper is not steadier

Raising instrument case depth from 300 to 400 mm feels like a stability upgrade, because the lever arm from the tipping edge grows. The geometry agrees: 8 more degrees. But equipment is not welded to the base, so a deeper box invites the load forward by about 50 mm, and half the gain disappears.

One criterion settles it: the horizontal distance from the load centre to the front bottom edge, divided by the centre height, gives the tip angle by arctangent. Depth, width and ballast all feed into that ratio, so no feel is needed.

Depth	Centre height	Load position	Tip angle
300 mm	180 mm	centred	39.8°
400 mm	180 mm	centred	48.0°
400 mm	180 mm	50 mm forward	39.8°
300 mm	240 mm	centred	32.0°
400 mm	240 mm	50 mm forward	32.0°

The third row is the point: 100 mm of extra depth buys 8°, and 50 mm of forward shift spends it. In the last row a 400 mm case with a 240 mm centre behaves exactly like a 300 mm case. Depth is a dimension; centre height is the variable.

2. Measuring the centre of gravity height

Slinging is quickest. Move two straps along the sides until the case hangs level, and the crossing point of the strap lines marks the centre; its height above the base is the centre height, repeatable within 5 mm. An 18 kg instrument case usually sits 230 to 260 mm up, roughly 40 mm above the geometric centre.

Instrument case depth: a worker guiding a cutting die into a blue press, stacks of black liner pads on the wooden bench beside him, a safety notice on the machine

The three-point method belongs in an inspection sheet. Two platform scales under the front corners and one under the rear corner give three readings, and moment balance returns the fore-aft position and the height in one pass, repeatable to 2 mm.

Centre height is a sensitive input. At 300 mm depth a 240 mm centre gives 32.0°, and 260 mm drops to 30.0°, or 2° per 20 mm. Two degrees reads as noise in a lab and as a fallen case on a loading dock.

3. Fore and aft offset and ballast

Fore and aft offset is the quiet load along the depth direction. Shift the equipment 50 mm forward and the front feet carry 11.3 kg instead of 9.0 kg, while the rear feet drop to 6.7 kg, so the ratio moves from 1:1 to 1.7:1 and pad compression differs by 0.6 mm.

Where the ballast sits decides whether it helps. With the offset at the front, more weight at the front doubles the problem; the block belongs on the opposite side of the base. A 1.5 kg block drops the centre from 240 to 224 mm and returns the angle from 32.0° to 33.8°.

More ballast stops paying early. At 3.0 kg the centre falls another 12 mm and the angle gains 1.4°, but the case goes from 18 to 21 kg, past the 20 kg single-person limit, so two people or a trolley cost more than 1.4° is worth.

4. Handle position against the base

A handle centred on the lid carries the case level. Move it 40 mm forward and the case hangs 7° nose-down, so the wrist rolls 7° to compensate. Over 200 m it becomes a strain injury.

Instrument case depth: white injection moulding machines along a yellow aisle, a gantry beam overhead, pallets of cartons stacked on the right

The gap between handle and centre height is the swing arm in a carry: 300 mm handle, 240 mm centre, 60 mm gap, and a 12° swing leaves the front edge 35 mm off the floor. Close the gap to 30 mm and the same swing leaves 62 mm.

Fix	Added weight	Centre drop	Tip angle	Cost
1.5 kg ballast on the opposite side	1.5 kg	16 mm	32.0° to 33.8°	+8.3% gross weight
Equipment sunk 30 mm	0	30 mm	32.0° to 35.5°	30 mm more depth used
Case deepened 50 mm	0.6 kg	0	32.0° unchanged	+2.1 kg volumetric
Load shifted 50 mm forward	0	0	32.0° to 22.6°	front feet 25% over

Only sinking the equipment pays outright: no weight, no volume, 3.5° gained. It works by pulling mass to the base, costing 30 mm of layout space.

5. Vibration and three impacts along the depth

Road vibration runs fore and aft along the depth. A truck profile sweeps 5 to 200 Hz at 0.5 g, and a base at 0.35 friction slides about 12000 cycles in a 4 hour leg.

A deeper case spreads the same 50 mm offset over a longer base, so the front edge stress falls 22%, even though the moment reaches 900 kg·mm. The bill arrives elsewhere: 0.9 kg more shell weight, pallet slip rising from 8 to 12 mm, and one extra strap to stop the stack walking half a position.

The three impacts are start, hard braking and the loading drop. Braking at 0.8 g gives an 18 kg case 14.4 kg of inertia; after 0.35 g of friction, 8.1 kg of net push remains for the liner. At 60% compression over 40 cm² that push works out to 2.0 N/cm², inside the usual liner range.

The drop happens during loading, not transport. From 1.2 m onto the front edge, deceleration near 300 g makes an 18 kg case weigh 5.4 t for an instant, and the liner must compress 70% to absorb it. A 400 mm case puts the centre 50 mm further from that edge than a 300 mm case, adding 12% to the moment; sinking the equipment 30 mm pulls it back under 8%. Drop samples therefore have to be loaded the way the case travels, because centred data cannot vouch for an offset load.

Conclusion

Depth can be changed; centre height cannot be argued with. Measure the centre first, then set the depth, and use the tip angle as the gate: above 32° the drawing can stand as is, near 30° ballast is mandatory, and under 28° the layout itself has to move. Both numbers come from a scale and a pair of straps, never from the outline on the drawing, because the mass hides inside the equipment.

Ballast gets exactly one home, the base on the opposite side to the offset, starting at 1.5 kg and stopping when the centre has dropped 16 mm. Anything beyond that only pushes the case past the 20 kg single-person limit without buying angle back. Once the tip angle is known, instrument case depth is finally a decision rather than a habit.

This article discusses container-side specifications and design implications only, and does not cover any handling, loading or use of the contents.