HP-85A tape drive conversion

Rik Bos hp-fix at xs4all.nl
Wed Apr 1 04:37:28 CDT 2015

> -----Oorspronkelijk bericht-----
> Van: cctalk [mailto:cctalk-bounces at classiccmp.org] Namens Marc Verdiell
> Verzonden: woensdag 1 april 2015 7:36
> Aan: cctalk at classiccmp.org
> Onderwerp: RE: HP-85A tape drive conversion
> > So the roller on my -85A tape drive is marginally ok [.]. While the
> >second option would work, according to the video it "just barely makes
> >the capstan roller contact the bottom portion of the tape capstan
> >wheel". That concerns me, as if it's "barely making contact" I'm
> >concerned that over
> time
> >this would wear the capstan roller motor shaft and perhaps wear down
> >the wheel, not to mention potential vibration.
> It doesn't wear the shaft, does not cause vibrations. But it eventually
wears out
> the edge of the rubber replacement you put over the capstan (shrink tube
> surgical tubing in my case). Eventually it fails and you have to put a new
> Annoying.
> > So. two questions: What SHOULD the outer diameter of a good capstan
> > roller be on that drive
> Dunno. If you have a semi good capstan, can you measure it? Apparently
it's not
> critical, since I got the tapes working OK with a thin shrink tube coating
as well
> as a thick surgical tube coating.
> >does anyone have other suggestions for how to make the capstan roller
> "taller"?
> I can think of at least two solutions.
> Solution one is to glue a metal or plastic "puck" of the same diameter as
> bare roller on top of it before recoating it. It's simpler than machining
the cap I
> show in my video, but you still need to have someone machine a simple disk
> on a lathe. That should be pretty cheap.
> Solution two requires someone good at making rubber. It would be to cast a
> rubber cap of the right diameter and thickness, and  with a pocket on the
> bottom so you can slip it or glue it over the existing bare capstan. So
you would
> not need to machine anything, just slip it over the bare capstan. If
anyone knows
> about an outfit that can do this, or can explain to me how to cast rubber,
let me
> know.
> M

The last option wouldn't work because the top of the capstan would be to
flexible, which would prevent a constant drive of the tape roller.
I'm using a simpler method than I described in the original article, I'm
using a piece 10mm aluminum tube of the right length. 
Then machine the capstan to the right size ~8 mm (a little over size) and
press the tube piece with some 2k glue over the capstan.
When the glue is dried enough I machine the capstan to the right size, and
glue the rubber to it.

It's a little easier to do then the methode described in the original


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