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Ballast Trough Screw Lid
This is the 90 mm OD x 3 mm annular lid from the 'NEMA17 Hanging Wall Polargraph Drawbot' kit. It closes the Ballast Gondola Pen Hub's shot trough so the ballast can't fall out. Its 22.6 mm bore slides over the hub's 22.0 mm pen sleeve. A 30 mm OD thrust ring, 2 mm high, gives the two rotating line arms a smooth bearing face. Three M3x8 socket-head screws go through 3.4 mm holes on a 40 mm radius into the hub's M3 heat-set inserts, and six 1.6 mm radial ribs stiffen the plate.
🧩 Part of the NEMA17 Hanging Wall Polargraph Drawbot (seals ballast, thrust face for line arms) kit.
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