My new toy: HP85 - test-drb@ccmp.vtda.org

16 Jun 1999

...
  Tony Duell wrote:
>
> > FWIW the teeth on these belts are pitched at 0.080 inch - the standard
"mini
...
 > > pitch", unlike some equipment I have
which uses belts with the teeth at 0.081
...
    inch... 
 Can you really measure 1 thou difference on something like this? I would
 have thought the 'wrong' belt would have fitted anyway, since the rubber
 is somewhat elastic, and over the 20-or-so teeth engaged on a typical
 sprocket, you've only got an error of 20 thou... 

To answer Tony's question first, yes you can.  Take one of each belt and turn
them inside out, i.e. teeth on the outside.  (.080 inch from HP-85, .081 inch
...
 from can't remember the make of papertape punch
that was sold in the UK by Teleprinter Equipment.) Try and mesh the teeth of the two
belts.  It soon
becomes obvious which one has the larger pitch.  These belts, being
string-reinforced, are not very stretchy and it would be difficult to get a .080
to run on .081 pulleys.

...
 > In any case, how hard is it to make new sprockets
with the right pitch
> (or even skim a bit off the existing ones to reduce the diameter
> slightly)? If the 'right' belts are impossible to obtain, this would seem
> to be a sensible solution. 
It might be a solution.  In my Tektronix 4662 the belt is intact, but the pulley
has died (20 teeth)  I glued the old bits of (plastic) sprocket to the (metal)
hub but it was just inaccurate enough to drop a tooth here and there.  Result,
the plotter couldn't get at the pens because they were offered up to the pen
carrier at the wrong place...

It might be quite easy to _buy_ new sprockets for .080 pitch.  If not, I may ask
to borrow your lathe, dividing head, etc...

[Stan:]

...
  Actually, the proper belts for the HP-85 printer are
still easy to come
 by. It took just two phone calls and I found a company called Stock
 Drive Products in New Hyde Park, NY (516-328-3300). They ship these
 belts from stock, and it doesn't appear that they have a minimum order
 quantity (I ordered three of each of the two belts). The two part
 numbers are A6B16-175012 and A6B16-078012, and they cost about two or
 three dollars each.

Lucky you.  When I contacted Stock Drive Products, they referred me to their UK
agent, Davall.  Davall do not, as far as I can determine, stock the HP85 belts.

I found, eventually, another supplier, who said they could get the .080 and .081
pitch belts.  I told them what belts I wanted and they promised to fax me a
price, but I never heard any more.  When I next get around to looking at the
punch, I'll have another try...

Philip.