[GreenKeys] empty papertape reels (for 8-bit tapes)

[Jones, Douglas W]

From: john at toebes.com [john at toebes.com] -- Tuesday, August 4, 2020 10:48 PM

> In particular, I'm not 100% sure of the thickness of the outside of the reels.

I got out my trusty dial caliper and measured the critical measurements.  The inside faces of the reel are 1.025" apart, and consistently so, from rim to center.  The center hole in the hub measures 0.51" at one end and 0.525" at the other end.  The taper is almost certainly as required for the injection moulding process, and the 0.015" difference between the two ends is a measure of the required tolerance.

The rim of the reel is 0.09" thick at the edge, tapering to 0.1" just before the circular decoration.  The decoration is 0.01" high, with no apparent purpose other than aesthetics.  The rims taper from 0.1 thick just inside the decoration to 0.125 just outside the legs that set the distance between rims.  I'm pretty sure that the entire business of tapering the rims from center to edge is a matter of minimizing total volume while retaining adequate strength.

If you print this using a filament fusion printer, you'd be starting on a flat platten and building up.  That would basically force the outside of the rim to be planar, and your best bet would be to make the entire rim 0.12" thick and omit the taper.  If you print this with steriolithography, you could almost certainly get the exact taper of the original.

            Doug Jones
            jones at cs.uiowa.edu