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

[AKLDGUY .]

> ...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.

Any chance that the thread is British/Euro?
Many decades ago I scouted around the hardware stores and vehicle parts
stores here in Auckland and found a pipe fitting that could be screwed on
by hand, so the threads were either identical or very close.

The fitting was of brass and of the type that connects fuel line to
carburettor in vehicles. I can't remember whether I had to drill out the
hole or not, but do remember that the shaft was eventually a snug fit
inside it.

Since we in the still subservient (-; Brit colonies tend to have more
Brit/Euro stuff, maybe the thread was Brit/Euro?

73 de Neil ZL1ANM


On Tue, May 27, 2014 at 8:06 AM, Mike Hanz <aaf-radio-1 at aafradio.org> wrote:

> 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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