Transparent parts are the reason a model kit looks like a model kit. The opaque sprues are straightforward moulding; the clear canopy is where a kit is judged, and it is judged optically. A canopy with flow lines, a weld at the frame, or a haze from the release agent is returned by the modeller, not by the retailer, and the modeller is unforgiving in a way no QC department is.
We mould clear canopies, windows and lenses for scale model kits and display programmes, in PMMA, PS and PC, with the process controls that optical parts need.
Why clear parts are a different discipline
Three things that never matter on an opaque part decide a clear one. First, the flow: every weld line and every hesitation mark shows as an optical defect, so the fill has to be fast and steady with the gate positioned where the line lands on a frame rather than across the glazing. Second, the surface: the tool is polished to a mirror grade and vented to the cavity edges, because a vent mark on a canopy is a scratch the modeller sees. Third, the handling: release agents, dust and even the ejector pin marks that would be invisible on ABS show as bright spots on a clear part.
Material choice per part
- PS. The default for kit glazing: cheap, clear, and soft enough to trim with a knife the way modellers expect. Brittle at low temperature.
- PMMA. Harder and more scratch-resistant, for display models and canopies that are handled rather than assembled. Trims poorly.
- PC. For parts that need impact resistance, such as lenses on functional models. Softer surface, scratches in service.
Specification
| Canopy | PMMA or PS, mirror-polished tool |
|---|---|
| Window | PS, 0.5 to 1.0 mm, knife-trimmable |
| Lens | PC, optical grade, impact rated |
| Clarity | Haze and flow-line criteria per programme |
| Packing | Interleaved, dust-controlled |
| MOQ | 5,000 pieces per part |
| Lead time | 25 days after approval |
Tool requirements
A clear-part tool is cut and finished to a higher grade than the same part in ABS: the cavity is polished, the ejector system is designed to leave no witness marks on the glazing, and the venting is deeper at the last-fill area than an opaque tool would tolerate. All of this adds days to the tool build, which is why clear-part tooling is quoted at a premium to the same geometry in an opaque material and why the lead time is longer.
Packing: the part is fragile until it is glued
Clear parts scratch on contact with other clear parts, so the packing is part of the specification: interleaving tissue or a formed tray per part, with the parts bagged individually where the programme is a premium kit. Modellers also expect the protective film on some canopies, which is applied in-line and quoted as a separate process.
Trim and fit
Kit glazing is trimmed after moulding, and the fit to the opaque frame is what the modeller judges. A canopy that is proud of the frame by half a millimetre looks like a defect, and one that is sunk looks unfinished. We hold the canopy to the frame dimension with the shrinkage of the clear material measured per lot, because clear materials shrink differently from the opaque frame they sit against, and the fit is sampled against the buyer's frame part rather than against the drawing.
Compliance
Kit glazing declares to EN 71-3, and the clear materials carry no plasticiser and no heavy-metal pigments. Age grading for the kit follows the smallest part in the box, not the canopy, but the canopy's sharp trimmed edge after assembly is assessed under the same point-and-edge policy as any other part.
Related reading
Our polystyrene model sprues programme covers the opaque half of model kits, and the model kit category lists the full range.
