[ARC5] Parts needed for ARC-5/274-N - splines...

[Jay Coward via ARC5]

Mike said:

I'm 
not sure how the powers that be, or were, came up with the odd thread count per 
inch, as I discovered for the flex cable article on my website that the 27 
T.P.I. thread came from a 19th century standard for gas light fittings!

ARC history began before some of the engineers and technicians were born!?

Jay ;-)

 
 
 
-----Original Message-----
From: Mike Hanz <aaf-radio-1 at aafradio.org>
To: arc5 <arc5 at mailman.qth.net>
Sent: Mon, May 26, 2014 1:07 pm
Subject: Re: [ARC5] Parts needed for ARC-5/274-N - splines...


On 5/26/2014 1:55 PM, hwhall at compuserve.com wrote:
> Tom Kneitel's Surplus Conversion Handbook, 1970 edition, had a short note on 
an ARC-5 RX tuning adapter that seemed the best I've seen. It provides 
mechanical support for the coupling joint, which seems to be key to getting a 
good feeling control and one that places minimal strain on the coupling 
material.
>
> It requires making a short (3/4 inch) cylindrical fitting of brass or aluminum 
(could probably do it in modern hard plastics or composites, too), drilled & 
tapped 1/2 - 28 at one end to screw onto the RX tuning ring, with a 1/4 inch 
hole continuing through the other end. Making that is the hard part.

Trudat.  :-)   Tom must have misread his thread gauge as well, since the thread 
is actually 1/2-27.  1/2-28 makes an interference fit, and with fresh aluminum 
to aluminum contact may weld the two parts together through galling action.  I'm 
not sure how the powers that be, or were, came up with the odd thread count per 
inch, as I discovered for the flex cable article on my website that the 27 
T.P.I. thread came from a 19th century standard for gas light fittings! It 
persisted in electronic hardware in a number of places, including coax 
microphone connectors with the center soldered button.  You can buy a tap with 
that thread, but it counts as a "special thread" that is more expensive.


> A 1/4 inch dia short shaft extension goes in with enough length to touch the 
spline shaft when installed, and a piece of plastic tubing makes the coupling 
from shaft to spline (could use brass or copper, too, I suppose). Then just 
attach your favorite knob to the 1/4 shaft.

In a way, it is simply a home brew variation of the retention nut part 
of the command receiver local control at the bottom of 
http://aafradio.org/garajmahal/flex_drive_cables.html

It is certainly a more sound way to make the connection than having the 
shaft cantilevered out from the tuning capacitor.

     73,
  - Mike

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