[GreenKeys] Main shaft fiber gear

[Jerry Murphy]

Fiber gears (more accurately called phenolic gears) are very durable.  Check
your Model 14 and 15 machines to see how fiber gears hold up. The problem
with any gear that has its tooth form cut or ground into it is the expense
involved.  Lots of operations involved to get a finished product.  Teletype
replaced many of the fiber gears in the M28 line with molded nylon gears.  
A very expensive mold could turn out lots of inexpensive gears. No need to
cut gear teeth since the teeth are molded in.  The original M28 KSR/RO speed 
change and intermediate gearing sets consisted of a metal pinion and a fiber 
gear.  When all four gears were replaced with molded nylon gears the result 
was a quieter and cheaper gear train.  Nylon gears would eventually shows 
signs of wear while the corresponding metal and fiber gears would rarely show 
signs of wear.  (Nylon gear wear was most obvious on the smaller gear of the 
pair.)  Teletype recommended that nylon gears only mate with other nylon 
gears.  Combining metal or fiber gears with nylon gears was not recommended 
even though the combination would work. 

In the interests of systemwide compatibility, I would expect that a shop 
doing TTY repair and overhaul would replace perfectly good fiber gears (and 
their steel pinions) with late style nylon replacement gears.

In the end, the cheaper and quieter nylon gears won out over the more durable
but more expensive fiber and metal gear sets. 

Jerry Murphy


-----Original Message-----
>From: "John, W9DDD" <w9ddd at tapr.org>
>Sent: Oct 16, 2020 8:55 AM
>To: Green Keys <greenkeys at mailman.qth.net>
>Subject: [GreenKeys] Main shaft fiber gear
>
>A question for the folks that serviced 28s back in the day.
>
>As I'm still sorting through the haul from a year ago, I find I have 7 
>of 150439 60 tooth main shaft gears.  You don't find that in the 
>documents unless you have an early issue (1149B original).
>
>So the question is ... did these fail a lot and therefore was changed to 
>Nylon early on?  Why else would a person doing service have this many 
>when most of the other items in the batch were at quantity 2 (common 
>screws, nute and washers being an exception)
>
>
>-- 
>John, W9DDD