[GreenKeys] TD gears for the dual head 28 ASR

[Christian Gauger-Cosgrove]

Hellos:

While I know why people what to run their TTYs at 60 WPM, but quite
honestly, wouldn't it be easier to just keep it running at 100 WPM,
and just use a pair of UARTS and loop-TTL to TTL-loop converters to
make it transmit/receive at whatever speed one pleases?

Now, in a perfect world, a better, and more fun solution would be to
get two 28RT sets, one which has the punch geared for 100WPM, and the
reader with a gear shifter; the other 28RT set put with the punch on a
gear shifter and the (climbing head) reader geared to 100 WPM. Because
that would just look cool.


Cheers,
Christian




On 4 February 2013 17:15,  <gfmurphy at earthlink.net> wrote:
>
>
>
>
> Greenkeyers:
> There's been some discussion about gearing for the 28 ASR that is equipped
> with the dual tape reader heads. Presumably, the next owner might like
> to run the machine at 60 WPM. The standard 161293 gear set will run the
> keyboard and page printer at 60 WPM.  The tape reader gear set is another
> matter.  The problem is that Teletype Corp. never made 60 WPM gears for the
> dual TD base that is in this machine. They made 4 sets of gears: 107 WPM
> for 7.00 pattern, 67 WPM and 100 WPM for 7.42 pattern and 88 WPM for 8.5
> pattern. If there had been a requirement for 60 WPM gears, they would have
> made them. There was no physical or interference issue with making 60 WPM
> gears for dual head tape readers.
>
> The gear problem stems from the need to drive the 2 tape readers from a
> jackshaft. The jackshaft was required because of clearance issues. In
> order for the jackshaft to be turning in the proper direction, the shaft
> that drives the jackshaft has to be turning in the opposite direction.
> That shaft - let's call it the front-rear shaft - is the same shaft that is
> on
> every Model 28 ASR TD base.  The front-rear shaft transmits rotary
> motion from the TD base speed change gears to the tape reader. In a
> standard single head tape reader, the front-rear shaft rotates in a
> counter clock-wise direction as viewed from the front of the machine.
> In a dual head tape reader, the front-rear shaft rotates in a clock-wise
> direction. The opposite rotation is accomplished by changing the
> 'hand' of the gears. Let's look at standard 100 WPM ASR TD base gears:
> There is a 158002 steel pinion with 11 teeth and a 158001 fiber gear with
> 33 teeth. They are both right-hand gears. The 100 WPM gears for dual
> tape reader operation are the 170293 steel pinion with 11 teeth and the
> 170297 fiber gear with 33 teeth. They are both left-hand gears. So, even
> though the single head and dual head gears have the same number of teeth,
> the rotation of the front-rear shaft is different in each case. Check with
> Google or Wikipedia for further clarification of the 'hand' of gears.
>
> You cannot take a set of 60 WPM gears (158005 pinion and 158006 gear) and
> install them on a dual head tape reader base and expect it to work properly.
> The gears will fit but the front-rear shaft will turn in the wrong
> direction.
>
> Jerry Murphy
>
>
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