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Baseplates: corner pockets with screws leave 3 open edges a cell at 34.32, 34.73 and 38.95 mm #91
Description
What is left of #80 after #81. Found by re-sweeping #80's design on main c0dc948 (21,916 designs the page takes: pitches 30 to 60 every 0.01, one cell and 2 x 2 in one piece, holes 2, 2.5 and 3 mm, heads at their cap, with and without a 6 mm magnet).
What happens. With corner pockets (bm=bosses) and screws, three pitches are taken by the page, with no warning and Download on, and build with 3 open edges a cell (2 x 2 in one piece: 15, 9 and 6). The head size does not matter (34.32 leaks with a 3.2 and a 6.1 mm head). #80's own link is now refused (the default 6 mm head is over the 5.8 mm cap there) and builds closed at the cap, so #80's figures no longer apply.
Repros (Baseplates page; counts are the page's per-piece bad edges, open edges are in brackets; each confirmed in Chromium on c0dc948):
| Pitch | Design | One cell | 2 x 2 in one piece |
|---|---|---|---|
| 34.32 | 2 mm hole, no magnet: #pi=34.32&w=34.32&d=34.32&bw=400&bd=400&cn=none&bm=bosses&sc=1&sh=2&sd=6.1 |
A1:3 (3 open) | w=68.64&d=68.64: 15 open, plus 78 edges of the known kind on cell lines |
| 34.32 | the same under a 6 mm magnet from beneath: #pi=34.32&w=34.32&d=34.32&bw=400&bd=400&cn=none&bm=bosses&mg=1&md=6&ms=bottom&sc=1&sh=2&sd=6.1 |
A1:3 | |
| 34.73 | 2 mm hole, 4 mm magnet from above: #pi=34.73&w=34.73&d=34.73&bw=400&bd=400&cn=none&bm=bosses&mg=1&md=4&ms=top&sc=1&sh=2&sd=6.5 |
A1:3 | w=69.46&d=69.46: 9 open |
| 38.95 | 3 mm hole, 6 mm magnet from above: #pi=38.95&w=38.95&d=38.95&bw=400&bd=400&cn=none&bm=bosses&mg=1&md=6&ms=top&sc=1&sh=3&sd=9.7 |
A1:3 | w=77.9&d=77.9: 6 open |
Three pitches of 3,001 swept every 0.01 (10 designs of 21,916): a handful of pitches, not a range. For comparison, designs with an open edge: 10 on c0dc948, 18 on main 326cc48 and 325 on f319c83 (pitches with one: 3, 8 and 91).
Cause. A boss's top is a cap fanned from its corner, so a spoke runs to each vertex of the rounded corner (at about 35.8, 38.7, 41.8, 45, 48.2, 51.3 and 54.2 degrees). When a spoke passes a few microns from a corner of a cutter's wall at the boss's top, the sliver of face between is lost. At 34.04 mm that was the spoke to the fifth vertex, 4.5 microns from the 2 mm shank's corner; #81 put the shank's flats on the size, which moved that corner 0.035 mm and took 34.04 off the spoke, and the same spoke meets a corner of another cutter at these three pitches. The window is under 0.01 mm wide.
Possible fix. Medium, engine geometry: the place is the top cap of a quarter boss (extrudePoly(outline, 0, top) in buildPiece). The cap is convex, so it can be fanned from any interior point; pick the point the way fanCentre does, avoiding the corners of the cutters that stand at the boss's top, or, to keep the bytes of every design that builds closed now, refan only a boss whose cell comes out open. Add audit rows for the four links and a sweep of 2, 2.5 and 3 mm holes from 30 to 60 mm every 0.01.
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