HP-85A tape drive conversion - test-drb@ccmp.vtda.org

31 Mar 2015

...
  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 or surgical tubing in my case). Eventually it fails and you
have to put a new one. 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
the 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 part 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. 

Marc