[ARC5] Part 6743 - tuning cranks and flexible drive cables.

[Mike Hanz]

On 4/8/2011 6:13 AM, Leslie Smith wrote:
> While it's not possible to fabricate such a "nice" part as the original
> knob and crank (part 6743) it should be possible to make a functional
> item that isn't a dog's breakfast.  That's the good news.

You can actually make an identical knob if you have a lathe, the 1/2-27 
tap, and some steel stamping letters (the 6743 is actually engraved on 
the front, but a careful stamping will come close.)  I'll have the 
sketches and photos up by this afternoon.  You will, however, have to 
come up with a female spline or a reasonable facsimile for part 6788.  A 
piece of vinyl tubing pinned to the adapter might work fine.

> (27tpi is a REALLY
> strange thing.  Bendix or ARC or who-ever must have had an unusual
> combination of thread cutting gears in the workshop.)

Yeh...as I discovered (and noted in the article), that thread form was a 
standard only used for gas lighting in the 1800s, dying back until it 
was reapplied for these radio control cables in the late 1920s.  Perhaps 
there was a touch of nostalgia there by one of the ARC or Bendix or 
Signal Corps engineers - the rationale is lost to the ages now.  
Interestingly enough, most lathes still have a 27 TPI setting, at least 
the ones I'm familiar with.

Best of luck,
   - Mike  KC4TOS