[GreenKeys] AP Model 15 longevity

[jhhaynes at earthlink.net]

Whether the M15 is more rugged than the M28 might be a matter of when
the tests were done.  At the time when the M28 first became available
for civilian use the M15 was a thoroughly mature product.  Teletype
products, like most everything, are tested in the factory but that
doesn't show up all the problems that lead to part breakage.  So they
depended to some extent on reports from the field to know where to
focus efforts at strengthening the product.  And with arcane matters
like heat treating steel, it's possible that a batch of parts got made
that were not as strong as the designer intended.  (Or were stronger,
but more brittle)

The initial production of Model 28 equipment all went to the military.
They were especially desired by the Navy.  The M15 was quite problematic
for shipboard use - consider the mass of that type basket assembly
being flung around on a ship that is pitching and rolling.

Tools and techniques for design and analysis got better with time too.
Teletype had a Bell Labs-designed high speed movie camera they could
use to see, millisecond-by-millisecond, what the moving parts were
doing.  And I remember some technique that involved making models of
parts from clear plastic, which would do something when lighted
appropriately, and there would be colored bands showing where stress
was concentrated.  I don't think they ever made a whole typing unit
that way, but individual parts that were subject to breakage could
be analyzed and perhaps redesigned to eliminate concentrations of stress.



jhhaynes at earthlink dot net