[ARC5] Splines

[Mike Everette]

Back some years ago I removed several ARC-5 tuning cables from aircraft which were being used as ground maintenance trainers.  The sheaths were quite rusty and the spiral had split in numerous places -- probably because the sheaths were a tad too short when originally installed (imagine that).  The actual flex shafts were rusty as well.

Since these things were 20 feet long, I cut the spline ends off the cables thinking I would put 1/4 inch knobs over the cut-off ends.  They were a tad small for doing this and 0.220 inch would seem about right.

I thought about shimming them with thin brass; but before trying that approach I discovered that the actual spline sockets were pinned to the shaft end.

It was not difficult to drive out the pins; but care was needed to determine which end to drive because, as I remember, the pins were tapered.
If you were to drive on the wrong end, you'd likely never get the pin out.
Careful preparation will show you which end is correct.

Using a drill press, with a press vise to hold the spline end, I enlarged the hole on the "shaft" side to 1/4 inch.  BE CAREFUL.  Make sure everything is straight before drilling.  GO SLOW.  You do not want to drill all the way through the spline socket.

I then inserted brass 1/4 inch shafting and sweat-soldered it into the enlarged end.  An old-style 100-watt or larger "plumber's" soldering iron with a large tip worked well for this; or you could use one of the micro-flame torches.  I used regular rosin-core solder.  Paste rosin flux makes the job much easier.

There is no need to pin the new shaft into the spline.  With a tuning knob, the forces on the shaft will be far less than they were with the long cable and "coffee grinder" control head mechanism.

I also salvaged the screw-on bushings and jacket ends from the old cable sheaths.  

Reassembling all this, with a 1-1/4 inch diameter knob on the new shaft, makes a very fine and nice looking tuning device.  It's secure on the receiver and does not have objectionable wobble, unlike the original ARC "local tuning knob."  Plus the larger-diameter knob makes tuning a lot smoother than with the ARC knob.

Yes, it was a lot of work; but back then I had a bit more time to invest.


73

Mike
W4DSE






--- On Mon, 12/31/12, Mark McKeown <mmckeown at tde.com> wrote:

> From: Mark McKeown <mmckeown at tde.com>
> Subject: [ARC5] Splines
> To: ARC5 at mailman.qth.net
> Date: Monday, December 31, 2012, 8:10 PM
> I have some cable end splines that
> are the originals that were made to be swaged onto the ends
> of the cables.  The shaft ends are .220 od but the ends
> can be taken apart (they are two pieces) and a quarter inch
> shaft made to fit the spline part with a little work or you
> can just put a knob on them.  I would be glad to trade
> for aluminum frequency dials that fit a BC-450 control or
> what do you have? 
> 
> Mark
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