Monroe electromechanical calculators

[Jules Richardson]

On Fri, 2005-06-17 at 00:49 +0100, Tony Duell wrote:
> > Question - does anyone have service information for these machines
> > (yeah, right!) or useful tips on things to check over?
> 
> No psecific service information, but my first comment is that 99% of 
> problems with mechanical calculators are due to gummy lubricants. Worn or 
> broken parts are uncommon.

There certainly doesn't seem to be much sign of wear on this machine.
The plus/minus/manual carriage movement keys seem prone to jamming and I
need to figure out the source of that (possibly more foreign debris in
the mechanism somewhere)

> Serondly, do not spray it with Wanton Destruction 40, or anything else 
> for that matter. You will do a lot more harm than good...

I've been using sewing machine oil so far (which is the lightest stuff
I've got). I just wonder if leaving it in a (slowly circulating /
filtered?) bath of oil for a week or so would be useful for freeing
stuff up and getting all the dirt out...

 
> > So far I've found an acorn jamming up the works (!!) and lots of dirt,
> 
> An Acorn... What, a System 1, or an Atom, or a Beeb or an Arch, or what...
> 
> (sorry, couldn't resist...)

:-)

I have no idea how it got in there; there isn't really a sufficient gap
anywhere for such a thing to fall inside. And it was *very* well buried
inside the mechanism (almost as though someone stuck it in there for
fun!)

> > There's some earth leakage which would be useful to track down -
> > possibly a break-down in cable insulation? I've not worked out what the
> 
> Most of the time, that's due to tracking across the impregnated fibre 
> insulators used in things like the automatic on/off swtich. 

Aha, well I can isolate and test easy enough there without any severe
dismantling of things. Can anything be done to fix the problem (short of
making new insulators)?  

> Almost certainly a governor. Do not be tempted to bypass it, many of 
> these machines used series wound motors which will get up to a ridiculous 
> speed if not controlled and do considerable damage. 

Yep, I saw somewhere that 180rpm is typical for governed motor speed...

> > Can't say I've ever seen such a complicated thing. Electronic circuits
> > don't even come close in complexity :-) I don't think I'd be up for a
> 
> I've not seen this one, but from the mechanical calculators I have been 
> inside, there's typically the same mechanism repeated <n> times (digit 
> entry, accumulator register, etc, and some control linkages, which are 
> typically outside the side frames. There are a lot of parts, but the 
> complexity is not that high.

Yep, it's the bits outside the frames that are rather scary-looking! The
actual underside of the key bed doesn't look too bad. This machine's
fully automatic, so I suppose it's an extra stage of complexity over a
semi-automatic machine. It's got three registers, plus the multiplier
one.

> > pps. Anyone care to guess a date for this machine? I'd make a wild guess
> > at mid-50's but really don't know.
> 
> Sounds about right. Maybe a little later (early 1960s). 

Uh huh - digging around since posting that, it looks like circa 1962 is
about right.

cheers,

Jules