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Board F

Design Analysis

Wall thickness, polycap geometry, and the four-color injection ceiling shape every visible feature of the Wing Gundam.

6. Design Analysis: Engineering and Proportions

6.1 What I Looked For

The Wing Gundam stands approximately 13 cm at 1/144 scale, corresponding to an in-universe height of roughly 16.3 m. A single armor part runs 10–20 mm in its longest dimension, and panel-line widths are routinely 0.15–0.30 mm. I started with one question: which features of the kit's appearance are aesthetic choices, and which are forced by the molding process?

13 cm
Model height at 1/144 scale
0.8–1.5
Armor wall thickness (mm)
4
Max colors per injection machine
The complete Wing Gundam runner set showing the five primary color groups.
Figure 1. The complete Wing Gundam runner set showing the five primary color groups. Color blocking maps directly onto runner identity — each runner color is constrained by the System Injection machine's four-color limit, not by aesthetic preference.

6.2 Wall Thickness Governs Both Stiffness and Moldability

HIPS armor halves on the HG Wing Gundam are typically 0.8–1.5 mm thick. Below ≈0.6 mm the runner becomes prone to short shots (incomplete fill) during injection because the melt freezes at the cavity wall before reaching the far end of the cavity. Above ≈2.0 mm the part suffers visible sink marks on the show-side surface from differential cooling between the surface and the part interior. The 0.8–1.5 mm range is the solution to "stiff enough to survive snap-fit insertion forces" and "thin enough to mold cleanly at HG cycle times."

Design Constraint

The 0.8–1.5 mm range is the simultaneous solution to two problems Bandai cannot escape: melt fill at one extreme, surface sink at the other. Thinner kits would need different tooling; thicker kits would lose the panel-line crispness that gives GunPla its visual signature.

6.3 Joint Location Is Constrained by Polycap Geometry

Because polycaps are molded as discrete LLDPE inserts, every articulating joint on the kit must be sized around the available polycap inventory. Inspection of the runner shows that the HG Wing Gundam reuses approximately six distinct polycap shapes for shoulders, elbows, hips, knees, ankles, and the wing-root pivot.

This re-use is itself a manufacturing constraint: it minimizes the number of distinct PE molds and standardizes joint resistance across the kit. A designer who wanted a unique joint geometry at, say, the elbow would either have to commission a new polycap mold or compromise the design back onto the existing inventory.

Figure 2. The PC7 polycap runner flexed by hand. Several bushing geometries are visible on the same frame; polymer ID for PC7 is FTIR in Plastic Origin §3.4, while this figure is about reusable joint geometry.

6.4 Color Blocking Maps onto Runner Identity

The five primary colors of the kit — white (large surface armor), blue (boots, chest detail), red (shield, accents), yellow (V-fin and trim), and black (joints, weapons) — are constrained by the System Injection machine's four-color limit. The layout team decomposes the design onto runners that respect that constraint.

Notable Case

The Wing Gundam's V-fin is one of the smallest and thinnest parts in the kit; its molding tolerance is the limiting case for the entire mold tool. Black HIPS runners commonly carry a higher load of carbon-black pigment (≈2 wt.%), slightly raising the modulus and lowering surface gloss compared with the white runner.

Front view of assembled Wing Gundam head showing the V-fin.
Figure 3. Front view of the assembled head. The V-fin is one of the thinnest, smallest features in the kit and is the limiting case for the mold tool's filling tolerance.

6.5 Gates and Fill Paths

Macro photo of runner gate marks at cavity entry.
Figure 4. Macro of the runner surface where the gate fed the cavity — the vestige at the sprue attachment is where melt entered. Gate position sets fill path; for thin cavities it dominates short-shot risk.
SB-13 runner with a long slender molded part held in tweezers.
Figure 5. SB-13 runner section with a long, slender molded part. Long thin geometries are among the hardest shapes to fill without warpage; tooling typically uses centered or symmetric gates where possible.