Most custom case projects stall in the same place. A buyer emails a factory with a photo of a handheld terminal and a question about price, the factory replies asking for 3D files, and the buyer discovers that the device OEM will not release CAD to an accessory maker. Six emails later nobody has a number. Working out what files to send a factory to quote a custom device case is the step that unblocks it, and it is mostly a matter of knowing which of four different inputs you can realistically supply.
A moulder is not being obstructive. A protective case is a negative of a solid, and the price of that case is set by the volume of the cavity, the number of side actions the apertures force into the tool, the wall thickness the geometry allows, and the cycle time that follows from all three. Without geometry, a quote is a guess wide enough to be useless to both sides — one of the main reasons quotes for the same spec come back so far apart.
Three things a quote actually depends on
Before assembling files, understand what the engineer on the other end is trying to extract. Every case quote resolves into three inputs.
Outer geometry of the device. This sets the cavity. It also sets the wall thickness available: a case that has to fit an existing dock or a pocket has a hard outer limit, and the device inside sets the inner limit. The distance between them is your entire design freedom, and on a slim device that gap is often under two millimetres.
Functional apertures and features. Every port, camera, scanner window, speaker, microphone, vent, button, battery door and SIM tray. Each aperture is a decision in the tool. Apertures on a face perpendicular to the pull direction are cheap; apertures that require a slide or a lifter are not, and three of them can move a tool into a different price bracket.
The commercial frame. Quantity and forecast, hardness, colour, decoration method, packaging, destination market, target price. Customisation on a moulded case usually spans shape, colour, logo, texture and port placement, and each of those is a cost line rather than a free option.
If you send geometry without the commercial frame, you get a tooling number and no unit price. If you send the commercial frame without geometry, you get nothing usable at all.
The four ways to give a molder geometry, ranked
| Input you can supply | What the factory does with it | Quote accuracy | Typical friction |
|---|---|---|---|
| Neutral or native CAD solid (STEP, IGES, Parasolid, native part file) | Offsets the surface directly to build the case solid | Highest — tooling and unit price both firm | OEM will often not release it to an accessory maker |
| 3D scan of the physical device (mesh: STL, OBJ, PLY) | Re-surfaces the mesh into a usable solid, then offsets | High, once the mesh is cleaned | Scan quality varies; re-surfacing is engineering time |
| The physical device shipped to the factory | Scans or measures it in-house and models from that | Highest of the three practical routes | Shipping time, customs, battery restrictions |
| 2D drawings, photos and hand measurements | Reconstructs an approximate model | Budgetary only — expect it to move | Cheap and fast, but do not sign a PO against it |
Two practical notes on that table that catch people out.
A mesh is not a solid. An STL carries triangles and nothing else — no units, no datums, no feature history. The unit problem is the classic one: a file exported in inches and read as millimetres is wrong by a factor of 25.4, and the failure is silent because the geometry still looks correct on screen. Send scan data with a written note of the units and one known reference dimension the factory can check against, such as the overall length measured with calipers.
Shipping the device is often the fastest route, and it is the one buyers hesitate over for the wrong reason. The real obstacles are logistical, not commercial: a device with an installed lithium battery is a dangerous-goods shipment by air and needs the right declaration and packing, and a used commercial terminal can attract customs attention on both legs. Sending a dead unit, or an identical unit with the battery removed and declared, avoids most of it. Ask the factory to confirm they will return it and put that in the same email.
If the OEM will not release CAD
This is the ordinary case for accessory brands, and it has three workable answers.
The first is scanning. A structured-light or blue-light scanner will capture an external shell to a resolution well beyond what a silicone case needs. The awkward parts are the surfaces: glossy black plastic and glass both reflect rather than return the pattern, so the device is normally dusted with a removable matte spray before scanning, and a glass display generally has to be re-established as a flat plane in CAD rather than trusted from the scan. Ask whether the factory scans in-house or subcontracts it, and ask what happens to the scan data afterwards.
The second is measurement plus photographs, which is only worth doing for a budgetary number. The third is the OEM itself: device makers with an accessory programme frequently will release a dimensional drawing or a simplified shell model under NDA, even when they will not release full CAD, and nobody asks.
The RFQ packet: everything that is not geometry
Geometry gets you a tool price. This list gets you a case that works. Assemble it once and reuse it for every supplier you approach, which also makes their quotes comparable — the same discipline as writing a proper spec sheet for a Chinese factory.
- Device model and hardware revision, plus the regional SKU. This is the detail that causes more respins than any other. The same commercial model number can ship with a different port arrangement, a moved antenna window or an extra sensor cutout between hardware revisions and between regional variants. Name the exact unit, and if you sell into several regions, say whether one case has to cover all of them.
- The accessory ecosystem the case must survive. Charging cradle or dock, multi-bay charger, belt clip, hand strap, shoulder strap, tether point, stylus silo, scanner sled, vehicle mount. Photograph each one and send the dock itself if you can spare it. A case that fits the device and not the dock is a complete failure that looks like a success right up until deployment.
- The cable and charger you actually ship, including the overmoulded strain relief. Port apertures are sized to the connector boot, not to the bare plug.
- Screen protection stack-up. Whether a tempered protector is applied under the case, and its thickness. It changes the bezel lip height, and on a curved-edge display it changes whether a raised lip is possible at all.
- Environment and duty. Indoor retail, outdoor field trade, cold store, vehicle cabin, wash-down. Cabin heat and ultraviolet exposure point at a different silicone grade from a warehouse scanner that lives at room temperature.
- Thermal behaviour. If the device runs warm — a thermal camera, a scanner in continuous read, an edge compute box — say so and identify the hot face. Vent channels and heat-dissipation structures are a design input, not something to bolt on after tooling.
- Hardness, colour and finish. Target Shore A, colour references, gloss or matte, texture, and whether colour has to match an existing housing.
- Decoration. Logo method, artwork in vector, placement, and how many colours.
- Commercials. First order quantity, annual forecast, SKU and colour split, packaging and labelling, destination ports, target landed price, and the date you need production parts on a shelf.
Send it as one PDF plus a folder of files with sane names. A packet that arrives as fourteen phone photos in six emails will be quoted more slowly and more defensively than the same information sent once.
Before you send: the file-protection questions
Your 3D data and your device photographs are commercially sensitive, and a case programme telegraphs a product roadmap. Handle it before the first transfer rather than after.
Sign an NDA with the legal entity named on the business licence, not with a brand name or a salesperson's email domain. On CMH, WJM Silicone's registered entity is on file as 深圳市维嘉美橡塑电子有限公司, and matching the counterparty on your NDA to the entity on the licence — and later to the bank account on the invoice — is the cheap version of due diligence. Ask whether the supplier has a standard bilingual template; if the only version offered is English, have a Chinese-language counterpart executed as well, because that is the version a mainland court will read.
Three clauses earn their place in a case-tooling NDA: what happens to your 3D data at project end (returned, deleted, or retained for spares), whether the moulder may sell parts from your tool to anyone else (the same ground covered by the tooling ownership agreement), and whether the design derived from your data may be listed in a public-mould library. That last one matters specifically in this trade, because a moulder's public-mould library is an asset built from past projects. The wider question of protecting IP with a Chinese factory covers the enforcement reality; the narrow version here is simply to be explicit about ownership before the files move.
Common questions
What if my device already has a case on the market?
Then say so and send that case as a physical reference alongside your device. A moulder can scan an existing case in minutes and tell you what it would cost to make, and more usefully what is wrong with it. Be careful about the instruction you give: asking a factory to copy a competitor's case is a different request from asking it to fit the same device, and only the second one is safe to put in writing.
Do I need a case drawing, or just the device model?
The device model is enough to start. The case drawing is the factory's output, not your input — the inner surface is derived by offsetting the device solid, and the offset value is a manufacturing decision that depends on hardness, wall thickness and how tight you want the fit. Ask which offset they applied and get it back on the case drawing for approval, because that single number decides whether the case slips on or fights.
How long should quoting take once the packet is complete?
Ask for a date rather than assuming one. A supplier with in-house mould design — WJM lists a 12-person R&D team covering 3D modelling, structural analysis, material selection and thermal simulation — is quoting from its own engineers rather than relaying questions to a subcontractor, which usually shortens the loop. What you want in the reply is a tooling price, a unit price at your stated quantity, a lead time, and a note of any feature they think will force a slide or a lifter into the tool.
What to ask the supplier next
Send this with your packet and keep the answers on file:
- Which CAD formats do you accept, and can you work from a mesh if I have no native CAD?
- Do you scan physical devices in-house or subcontract it, and what happens to the scan data afterwards?
- Is there a scanning or design fee, and is it credited against tooling?
- What inner offset will you apply to the device solid, and will you show it on the case drawing before cutting steel?
- Which apertures in my design force a side action, and what would each one save if I moved or resized it?
- Do you have a bilingual NDA template, and will you execute it in the name on your business licence?
- Will my 3D data be returned or deleted at project end, and may the resulting tool ever produce parts for anyone else?
Send a device model, 3D files or a written brief to a factory that designs and cuts its own tooling and the reply should contain numbers rather than more questions — WJM Silicone in Longgang, Shenzhen is one of the direct-contact manufacturers on CMH that quotes from its own mould shop rather than through a trading layer. Once the quote arrives, the fit and cutout tolerances you agreed in the packet become the criteria your first sample gets measured against — and there is a separate discipline for reading that first sample before steel is cut.