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

[Leslie Smith]

Hello Mike,
Thank you for clarifying the detail to the questions I asked below, and
in particular noting that the threads are 27tpi, not 28 tpi.  Before
this I ran a thread gauge over the exposed threads on the receiver, and
decided they were 28tpi.  Not so, and looking at the drawing "mechanical
linkage assembly" (also called "ARC-5/SCR-274N/ARA" drive cable
details") I now note the arrow pointing to BOTH views of part number
1167 (the locking nut/device).  Those two arrows (with the dimension 1/2
27tpi) make the detail crystal clear, and my questions were
un-necessary.

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.  I see that
you purchased a 1/2 27tpi tap.  That's good news too.  I spent a good
deal of time trying to find the wrong one (28tpi) here in Australia.  At
least I know the 27tpi taps are available in USA.  (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.)

Thank you for the drawings on your web-book, and the further detail in
your reply below.

Best wishes,

Les Smith
ex VK2BCU

(end)


-- 
  Leslie Smith
  vk2bcu at operamail.com


On Fri, 08 Apr 2011 05:41 -0400, "Mike Hanz" <aaf-radio-1 at aafradio.org>
wrote:
> On 4/8/2011 2:24 AM, Leslie Smith wrote:
> > Tuning cranks and drive cables.
> >
> > http://aafradio.org/garajmahal/flex_drive_cables.html
> >
> > Mike Hanz has published a page giving details for the Bendix flexible
> > drive used in various sets, including what we call "command"/ARC-5 sets.
> >
> > I am trying to understand these drawings, and the fabrication of these
> > cables.  As I understand the drawing, the thread used to fix the
> > flexible cable on the ARA, SCR-274 and ARC-5 receiver families is 1/2
> > inch x28 threads per inch.  I would like to recieve confirmation that I
> > understand this correctly.  (The other alternative is 27 tpi, and Mike
> > seems to discount this for the "command" sets.)
> 
> I should probably have clarified the narrative a bit more, Leslie.  The 
> Bendix style section that comprises the first part of the web page is 
> the larger flex cable that one finds in WWII and earlier aircraft, not 
> that used on the command sets.  Note that the threads are all 5/8" in 
> diameter.  You can ignore the first section if you are only interested 
> in the command sets, which starts at "Later ARC Flex Drive Tuning Cables 
> (the "miniatures")".  In the drawing below that, the knurled nut shows a 
> thread of 1/2-27.
> 
> > I would like to find a detail drawing for the tuning crank, ARC-part
> > number 6743.  Can any-one on this list tell me if a drawing of this part
> > exists, and if "yes", where I can find this drawing?
> 
> Since I just finished restoring a 6743 that had serious corrosion 
> issues, I'll add a quick sketch to the bottom of the web page when I get 
> back this afternoon.  I have never seen an official version.
> 
> > In the absence of a drawing, I turn to the drawings and photos from the
> > web-page above, "flex_drive_cables".  A drawing is given of the cable
> > assembly, "ARC-5 drive cable details" and that drawing (3rd from bottom
> > of page) shows a female splined end, part 6788.  I believe this slips
> > over the male spline on the receiver.  This is the end of the 3 gang
> > tuning capacitor.
> >
> > Is my understanding correct?
> 
> That is correct.
> 
> > Assuming the detail in the paragraph above is correct, can anyone give a
> > source for a female splined end?
> 
> I have never found a source for these, at least not from current 
> manufacturers.  There are some moldable materials that might be used to 
> make some, using  the end from the receiver variable capacitor as the 
> internal pattern, but I have never pursued it very far because I have 
> found what I needed at various times.  There was a member of this list 
> who was looking into using a wiggle broach at his work to make some, but 
> I don't know the status of that at the moment.
> 
> > Turning to other items in the Mike Hanz' drawing ("ARC-5 drive cable
> > ..." consider part number 1167.  This looks suspiciously like a locking
> > device that might hold a tuning crank in place.  I believe the internal
> > thread in this locking device is 1/2 inch 28 threads per inch.
> >
> > Is my understanding correct?
> 
> No - it is 1/2-27.  All of those threads mentioned on that page are what 
> is referred to as "special" threads and taps are available if at 
> somewhat higher prices.  Here are two I bought just recently on sale 
> from MSC Industrial Supply (mscdirect.com), but I think their normal 
> prices are almost double that:
> 
> 04844221     1/2-27 HSS HAND PLUG TAP      $17.28
> 66556168     1/2-27 HSS HAND BOTTOM TAP     $15.28
> 
> Most of these special taps are Chinese imports and need some dressing of 
> the tip to make them work well, but using them in aluminum isn't too 
> bad.  Note that a tapped sleeve is needed to approach a knurled nut if 
> you want a clean start and well finished thread.  Otherwise you tend to 
> get a tapered thread.
> 
> 73,
> Mike  KC4TOS
> 
> 

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