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

[john at toebes.com]

More good measurements.  I've updated the model at
https://cad.onshape.com/documents/debbba2925a167ad85461476/w/ce2487daaffd99c
0fbdff960/e/27715fe3df49726eee4106f7 
(note you don't need an Onshape account to view it) and generated a drawing
showing the measurements that I think matter.  Feel free to point out
anything that I got wrong.  

Thanks!
  -- John Toebes

-----Original Message-----
From: greenkeys-bounces at mailman.qth.net <greenkeys-bounces at mailman.qth.net>
On Behalf Of Jones, Douglas W
Sent: Wednesday, August 5, 2020 12:03 PM
To: greenkeys at mailman.qth.net
Subject: Re: [GreenKeys] empty papertape reels (for 8-bit tapes)

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
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