[ARC5] Part 6743 - tuning cranks and flexible drive cables for the ARC-5 sets.

[Leslie Smith]

                    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 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?

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?

Assuming the detail in the paragraph above is correct, can anyone give a
source for a female splined end?  I don't refer to a surplus or NOS
cable, or a part from the ARC-5 component list, but simply a part that
can be adapted to make a "nice" but non-original tuning crank or
flexible drive.  I'm sure I can get ONE splined thing-o, but what if I
want two or a dozen?  NOS is not a possibility here.  I have spoken with
a competent tradesman, on the subject of fabricating the spline.  His
opinion:  A tool to broach as many female splines as I want can be
easily got - for about $1000.  Probably correct, so I will look
elsewhere for a solution.

There are plastic solutions available, of course.  A length of common
flexible air line (eg Festo) will fit over the spline nicely, and could
be pressed into service for little cost.  A nice fit, but not such a
nice thing to put on a "command" receiver, I'm sure.

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?

To make this thread I will need a 1/2 inch 28 tpi tap.
Can anyone on this list tell if these can still be bought?
I found a #12G 28 threads per inch from a local supplier, (Blackwoods)
but I have no idea about the diameter of a #12 gauge tap.  

Is there a possibility that #12 gauge is 1/2 inch?

I see no other tapping tool from Blackwoods with the correct diameter or
tpi.  Blackwoods supplies an extensive range of tools, and if a tap
isn't available from here, then it ain't to be got.  I would rather buy
a tapping tool than try to adapt a butchered cycle axle as a tap.  I'll
say no more than that.

Looking forward to interesting and well informed replies!


Les Smith
ex VK2BCU

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