[ARC5] Bowden tuning cables problem

[Richard Hankins]

Folks,

thanks for all the ideas.   I think the worst of these cables has a 
length difference between inner and outer of some 3 inches.   I will 
certainly try the oil, flex and stretch idea.  I certainly won't modify 
them.

Richard


On 26/03/2013 16:00, Kenneth G. Gordon wrote:
> On 26 Mar 2013 at 8:49, Richard Hankins wrote:
>
>> I have just obtained some of those hard-to-find Bowden tuning cables
> I am almost certain that "Bowden" is not the correct term. However, we know
> what you mean.
>
>> used on SCR-274, etc.   Having just tried several on a set and control
>> unit, I find they are unusable in their current form.
> That is not unusual...
>   
>> The problem is that the inner is too long relative to the outer. I can
>> assemble one end just fine, and it all works as expected. But the
>> other end cannot be assembled because the locking ring doesn't get
>> anywhere near the collar on the set/control unit.
> Yes. That is a common problem. I recently sold three 78" long MC-215s for
> use in a restoration of a Curtiss P-40 fighter aircraft through one of our
> members here which looked like that...until I worked on them a bit.
>
> Mine still had the original yellow tags on them and the ends were still
> covered with the original chemically impregnated tape, and there was still the
> original grease in the ends and along the length of the inner cable.
>
>> I presume I have cables intended for some other application, where the
>> spline is buried much further into the equipment.
> No. That is not the problem.
>   
>> Anyone know if its possible to modify these cables, and if so, how you
>> do it?   I hope it can be done, because they are otherwise in good
>> condition.
> What you will need to do is as someone else here mentioned: 1) throughly oil
> the outer sheath, removing as much corrosion as possible in the process.
>
> Then, 2) work each "joint" in the spiral of the sheath back and forth several
> times, over the entire length of the sheath. While doing this, you will hear or
> feel something "letting go". Each "joint" may even snap or crack as the
> corrosion that locks each joint releases.
>
> 3) When you have finally gotten the sheath as flexible as you possibly can
> make it, lock one end in something that you can pull against, and pull the
> outer sheath gently but firmly until its over-all length extends to the "correct"
> length.
>
> You may have to oil it and "work" it repeatedly until you get enough "stretch"
> (it isn't really "stretching", by the way). You may also wish to work the sheath
> up and down over its entire length as you pull on it.
>
> When those cables were made, the outer sheath and the inner cable were
> made correctly and about the same length. Over the many years since, the
> natural springiness of the sheath caused them to become compressed or
> "pulled together", and corrosion then locked them in that position. What you
> are doing is restoring them to their natural length against their natural
> springiness and the corrosion.
>
> But be careful: you don't want any of the spiral joints to completely separate.
>
> Please don't "modify" those. They are getting almost impossibly difficult to
> find.
>
> I have a product called "Evapo-rust" here that I have used to soak such
> cables in. It dissolves not only rust, but other forms of corrosion as well, and
> made my cables much easier to work with. When I finished with them, they
> looked almost new.
>
> Ken W7EKB
>