Sand table v2: printable design, STLs and notes

12" polar kinetic sand table (motor-on-arm mechanism with slip ring).
- SolidCraft design + STEP assembly
- 25 print-ready STLs for a Bambu P1S, fits set from the fit-test coupon
  (shaft 8.1 mm, 608 pocket 22.2 mm)
- design notes: mechanism, dimensions, BOM, hardware, print orientation

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.gitignore

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+# SolidCraft auto-backups
+*.bak
+
+# OS / editor cruft
+.DS_Store
+*.swp
+*~