What tolerance should a custom foam instrument case carry inside?

Answer: Plus or minus 1.0 mm for injection moulding, 2.0 mm for rotational moulding. Tighter and the supplier sorts parts; looser and the foam thickens.

Can die spacing be cut to 4 mm?

Answer: Not advisable. A 4 mm bridge collapses during cutting and the corner cracks first, unless the cavity is shallow.

How do draft and depth convert?

Answer: Multiply the per-side angle by depth. At 2 degrees and 80 mm, each side loses about 2.8 mm, so the floor is 5.6 mm narrower.

Which line is most often missing?

Answer: Clear height. Drawings state case depth but forget base and lid foam, and the sample arrives touching the lid.

Does small volume work to the same specification?

Answer: Yes. A die spreads past fifty pieces; below that, routing avoids tooling cost but leaves marks.

Custom Foam Instrument Case Specifications: Sizes, Walls, Load

Quick answer: A custom foam instrument case is fixed by four things first: three internal dimensions with tolerances, die spacing, draft angle and drawing checks. Wall thickness and load follow from those.

The Specification Sheet for a Custom Foam Instrument Case Has Five Parts
Internal Size and Tolerance: Three Dimensions, No Shortcuts
Die Spacing and Wall Thickness
Draft Angle and Cavity Depth
Drawing Checks and Acceptance
FAQ

1. The Specification Sheet for a Custom Foam Instrument Case Has Five Parts

Drawings for a custom foam instrument case split into five parts: space, shell, foam, hardware, marking. The first two decide whether the instrument fits.

Each part is written differently: space and shell carry tolerances, foam carries spacing and layers, hardware carries loads, marking only position and colour. Tolerances are the step most often skipped.

Part	Must state	If left out
Space	Mouth, base, clear height, tolerance	Will not fit, or rattles
Shell	Wall, parting line, ribs	Sags under stacking
Foam	Material, density, layers, spacing	Thin walls crack
Hardware	Latches, handle rating, hinge	Seats split in transit

2. Internal Size and Tolerance: Three Dimensions, No Shortcuts

One length by width by depth is not enough. The mouth decides entry, the base how much slack remains, clear height how much room the foam leaves.

Custom Foam Instrument Case: dark grey case closed on grey gradient, centred handle, a latch each side, round pressure valve, ribs around the lid

Injection shells take plus or minus 1.0 mm, rotomoulded 2.0 mm. Injection walls are uniform; rotomoulded walls vary with powder dwell time, up to 0.6 mm around one mould.

Draft eats height: at 1.5 percent over 400 mm, the base is 3 mm narrower per side and 6 mm shorter. A custom foam instrument case drawing names both mouth and base sizes, or the draft and its datum.

Foam takes more. With 25 mm in the base, 15 mm in the lid and 3 mm of compression, a 120 mm deep case leaves 77 mm of clear height.

3. Die Spacing and Wall Thickness

Spacing is the solid foam between cavities, or cavity and wall. Die-cut cavities sit at least 6 mm apart and 12 mm from the wall; narrower and the wall shears. A bridge under 5 mm collapses, while 6 to 8 mm holds.

Depth changes the figure: beyond 60 mm of cavity depth, walls go to 8 mm, or the foam lifts with the instrument.

Location	Minimum spacing	Why
Between cavities	6 mm	Die bridge width
Cavity to shell wall	12 mm	Corner squeeze
Floor to case floor	12 mm	Impact on landing

4. Draft Angle and Cavity Depth

Foam draft is not mould draft; it is the sidewall angle left by the die or router. A custom foam instrument case runs 1.5 to 3 degrees, and a straight wall will not pull past 40 mm.

Custom Foam Instrument Case: dark grey case split open on pale grey, flat foam in lid, long cavities in base, handle and two latches

Shell draft counts separately: 1 to 2 degrees per side for injection, 2 to 3 for rotomoulding. Foam following the shell sits better, but deep cavities need another 0.5 degree.

Draft changes capacity. A cavity 100 mm square and 80 mm deep at 2 degrees measures about 94 mm at the floor; drawn at the mouth, the base is 6 mm tight. Floor margin: 12 mm to one kilogram, 20 mm above five.

5. Drawing Checks and Acceptance

Six checks run before a drawing leaves the office; most rework starts here, and one wrong cavity scraps the die.

Check	On the drawing	How to verify
Three internal sizes	Mouth, base, clear height, tolerance	Caliper each, take smallest
Wall thickness	Nominal plus allowed thinning	Three points per face
Foam density	kg per cubic metre, plus or minus 3	Cut, weigh, convert
Cavity spacing	Narrowest solid width	Caliper the narrowest point
Load and stacking	40 kg for 24 hours, three high	Watch for 2 mm of sag

Acceptance starts at the internal space, then spacing and draft, then latches and handle. Load is tested alone: 40 kg over the lid for 24 hours under 2 mm of sag, stacked three high.

Conclusion

Three groups of numbers define a custom foam instrument case: internal sizes with tolerances, spacing with draft, load with stacking limits. Leave one out and the supplier fills it by habit.

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.