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

[J. Forster]

The outer part of the adapter is a little cup, threaded internally.

FWIW, it's pretty hard to tap such a thing, and will need at least two
taps, the second being a 'bottoming' tap.

I suspect they were made on a turret lathe. IMO, a lathe is probably the
easiest way to make it, even today, something like this:

Chuck up stock.
Knurl the OD
Through drill 0.25"
Bore ID to depth
Thread ID
Cut off finished part.

Next...

-John

==================




> "the thread is actually 1/2-27."
>
> Thank you! I'm very glad to learn that, as I had considered buying a tap
> to experiment with making an adapter. I'd have bought the wrong item!
>
> Wayne
> WB4OGM
>
>
>
> -----Original Message-----
> From: Mike Hanz <aaf-radio-1 at aafradio.org>
> To: arc5 <arc5 at mailman.qth.net>
> Sent: Mon, May 26, 2014 2:07 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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