Mechanical Design: Trapezoidal Motion

Picked one by one from a mixed channel. Transcript check: both title readers certain; 5 of 5 sampled certain picks confirmed by transcript, none failed. Channel rule: Include only the dedicated engineering explainers (e.g. Limits and Fits, Mechanical Design series) and build-series parts whose transcript is mainly a walkthrough of design rationale and machining steps (Micro Lathe, Jeweler's Lathe, tool changer, injection molding, Reimagining Small Vises parts). Exclude updates, milestone and novelty toy builds, short clips, and anything tied to selling the Arcvise.