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Prototype · simulated, uncalibrated · synthetic part

Change one dimension. Rerun 5,000 units.

A two-part enclosure: the cover snaps onto four plastic hooks. As it goes on, each hook bends. Bend a hook too far and the plastic is overstressed, so it can crack or lose its grip.

01 · The part
Exploded view of a plastic enclosure: a dark cover lifted above a grey base with four snap hooks on its walls. Snap hook
Cover and base, joined by four snap hooks. No screws.
02 · How it snaps
The cover slides down outside the base, its edge pushes the hook inward until the bend peaks, then the head snaps out into the window in the cover. inside outside 1 Cover slides on 2 Peak bend 0.1 mm gap 3 Snaps into windowThe cover slides down outside the base, its edge pushes the hook inward until the bend peaks, then the head snaps out into the window in the cover.1 Cover slides on inside outside 2 Peak bend 3 Snaps into window 0.1 mm gap
The cover’s wall comes down outside the base with a 0.1 mm gap. Its edge rides over the hook’s ramp and pushes the hook inward 0.8 mm (0.9 mm undercut minus the gap), then the head springs out into the window.
03 · The risk, at peak bend
At peak bend the hook as drawn, 8.0 mm, reaches 2.74% strain at its root for the worst simulated unit, over the 2.5% limit. The twin's proposed fix, a hook 0.5 mm longer, reaches 2.43%. 8.0 mm 8.5 mm2.74%as drawnworst unit2.43%the twin’s proposed fixhook +0.5 mm

Same push, two lengths.

A snap hook is a small cantilever. Bending is worst at its root, and root strain grows with the push and shrinks with the square of the length:

strain ≈ 1.5 · t · y / L2

The cover pushes both hooks by the same amount. Making the hook 6% longer cuts its root strain by about 11%, which brings the worst simulated unit back under the 2.5% limit.

Red glow: the root of the hook as drawn is overstrained in its worst simulated unit. Gold points: the twin’s proposed fix, tested across the same 5,000 units. Undercut, clearance and deflection drawn enlarged so they read.

04 · 5,000 simulated units
5,000 simulated units, 50 to a square. As drawn, with the hook 8.0 mm long, 183 units strain the hook root past the 2.5% limit. With the hook 0.5 mm longer, none do. As drawn hook length 8.0 mm 183 of 5,000 over the limit The twin’s proposed fix hook length 8.5 mm 0 of 5,000 over the limit 50 simulated units over the 2.5% strain limit 5,000 simulated units, 50 to a square. As drawn, with the hook 8.0 mm long, 183 units strain the hook root past the 2.5% limit. With the hook 0.5 mm longer, none do. As drawn · 8.0 mm 183 of 5,000 over the limit The twin’s proposed fix · 8.5 mm 0 of 5,000 over the limit 50 simulated units over the 2.5% strain limit
Each square is 50 simulated units, every unit with its own part and station variation. Red marks the units whose hook root strains past the 2.5% limit. The twin’s proposed fix, a hook 0.5 mm longer, clears all of them.

Simulated and not yet calibrated against a real build. Synthetic part, not a customer’s. Strain is the model’s estimate for the worst of the four hooks. A full run of 5,000 units takes about 5.5 seconds on one CPU. This enclosure was the engine’s first test. The line viewer shows Plus One’s line at volume on a MadeCell 40. See all five builds →