Custom CNC foam inserts: how we engineer a perfect equipment fit

The plywood shell of a flight case gets all the attention — it's the part you can see, brand and stack. But when a case does its job, the component doing most of the work is the foam. The shell survives the impact; the foam decides whether your equipment does.

This is a look inside how we engineer custom CNC foam inserts at Nomad: how we get from "here's my kit" to a precision-machined interior where every item has exactly one home, held exactly firmly enough.

Why fit is protection

When a case is dropped, the shell stops moving almost instantly. The equipment inside wants to keep moving — and the foam's job is to decelerate it over distance. The physics is unforgiving: halve the deceleration distance and you roughly double the peak shock the equipment feels.

This is why fit matters so much. Equipment loose in an oversized cavity accelerates before it hits the foam, adding impact energy the foam then has to absorb. Equipment crammed into an undersized cavity has no foam travel left to cushion with — the foam is already compressed and transmits shock straight through. A correct insert holds the item with light, even contact and leaves the engineered thickness of foam free to do its decelerating.

Fit also solves the quieter killers: vibration (a held item can't rattle its connectors loose over 500 motorway miles) and abrasion (an item that can't move can't wear its finish off against the interior).

Step 1: capturing the equipment

Every insert starts with geometry, and we take it in whatever form you have:

CAD data — STEP or IGES files from the equipment manufacturer are the gold standard, and for kit like camera systems or bespoke electronics, most manufacturers will supply them on request.
Our measurement — send us the equipment, or for larger projects we measure on site. Critical dimensions are taken with digital calipers; complex curved bodies can be 3D-scanned.
Your measurements — workable for simple rectangular kit, and our pre-production checklist tells you exactly which dimensions we need, including the ones people forget: protruding connectors, switches, handles and feet.

We also ask questions geometry can't answer. Which face must point up? What gets unplugged last? Which items come out first at load-in? Does anything travel hot? The answers shape the layout as much as the dimensions do.

Step 2: choosing the foam

"Foam" covers a family of materials with very different jobs. The main decisions:

Closed-cell polyethylene (PE/PE-LD) is the workhorse for CNC work — typically 30–45kg/m³ density for general equipment protection. Its cells are sealed, so it doesn't absorb water, recovers well from repeated compression, machines to a clean accurate edge, and won't shed dust onto your kit. Most of our cut inserts are PE.

Cross-linked polyethylene (XLPE / Plastazote®) has a finer cell structure: firmer, cleaner-cutting, inert and low-abrasion. It's what we use against delicate finishes, lenses and anything bound for clinical environments — at a price premium that's justified when the contents demand it.

Open-cell polyurethane (PU) is the soft, compliant foam — think lid pads and convoluted ("egg-crate") layers that apply gentle hold-down pressure. It absorbs water and compresses permanently over time, so we use it for compliant contact, never as the primary shock layer.

Density is a calculation, not a guess. The right foam stiffness depends on the equipment's weight spread over its bearing area. A 2kg lens and a 40kg amplifier need different foam under them; put the amp on soft foam and it bottoms out, put the lens on hard foam and the foam never compresses at all. Where one case carries both, we build layered or zoned inserts with different grades bonded together.

Step 3: CAD layout

The cavity layout is drawn in CAD before any foam is cut. The same rules apply to a one-off as to a fleet:

Wall thickness between cavities sized to the weight of adjacent items, so one heavy item can't crush its way into its neighbour's space
Finger slots beside every item, sized for gloved hands where the case is crew-handled — an item you can't get out gets pried out, and pried-out items get dropped
Clearance tolerance of typically 0.5–1mm per side for a held fit, tuned looser for items removed dozens of times a day and snugger for items that ride long distances between uses
Orientation logic — heavy items low and central for case balance; first-out items nearest the lid; cable cavities so the case packs the same way every time, by anyone

That last point is underrated. A well-designed insert is documentation: the crew member who has never seen this kit before can pack it correctly at 1am, because every item visibly has one home.

Step 4: CNC machining

The approved CAD file goes to the CNC router. Machining gives us what hand-cutting never can: repeatability of ±0.5mm across every insert in a production run, stepped multi-depth cavities cut in one pass, true vertical walls, and clean internal corners.

Multi-layer builds are machined as separate layers and bonded, giving us full 3D control — a cavity can be PE at the sides for location and XLPE at the base for finish protection. Lid foam is cut to apply the right closing pressure: enough that nothing moves, not so much that the lid preloads the latches.

Step 5: fit check

Before any case ships, the actual equipment (or a verified dummy) goes into the actual insert. We check hold, removal effort, lid pressure and — for fleet builds — interchangeability across cases. If the fit isn't right, the file is revised and the layer recut. The CAD file is then archived, so a replacement insert or an extra fleet case years later matches the original exactly.

Start with your kit list

If you can send us a kit list and dimensions — or STEP files, or just the equipment itself — we can engineer an insert around it. Get in touch with the workshop to start a custom CNC foam insert spec for your next custom flight case, and have a look at our pre-production checklist so the first conversation covers everything in one pass.