Cassette reel demo

Dimensions, from the technical drawings. Reel hub flange ø21.5 mm, so the tape pack starts at 10.75 mm radius. Hub drive bore ø13 mm with six teeth. Tape width 3.81 mm. Shell thickness 13.0 mm. Shell 100.4 ±0.3 × 63.8 ±0.8 mm, hub centres 42.5 ±0.3 mm apart on the vertical centreline at 31.9 mm. I had previously read the 27.9 ±0.15 dimension as hub centre up from the bottom edge, which put the hubs 4 mm low and made a full pack reach past the tape path. Shell spindle apertures ø10 +0.4. Capstan holes 48 ±0.2 mm apart, inner pins 28 ±0.15 mm apart. Tape path 3.4 ±0.2 mm up from the bottom edge. Corner bosses 3 mm in from each edge, R2.5.

Tape constants. Pack inner radius 10.75 mm, tape speed 47.625 mm/s (1.875 in/s), full pack 24.63 mm radius. Packs clear each other by 4.49 mm at the tightest point, which is always the crossover, and a full pack sits 4.32 mm clear of the shell edge. Pack areas sum to the same total on every frame, which is the correctness check.

Tape threading. The ribbon is a taut belt, not a straight line. It leaves the supply pack on a true tangent, wraps the corner guide, runs along the underside of both guides, wraps the far guide and winds onto the take up pack. Only the corner guides are actually touched. The capstan holes sit 0.45 mm above the taut run and the inner pins 1.80 mm above it, so the ribbon passes cleanly beneath them rather than cutting through.

Source conflicts. The blueprint gives the shell as 100.0 × 63.5 and is marked reference only, while the IEC drawing gives 100.4 ±0.3 × 63.8 ±0.8 with tolerances. The IEC figures are used here. The ø13 hub bore and the ø10 shell aperture are different features, not a conflict.