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Thanks for the data point, Gary. Certainly the marine industry is a
much harsher corrosion environment than the inside of an airplane.
There's so much conflicting information out there that it's hard to
know whom to believe, but I can tell you one thing: Over the last
few days I've learned a lot more about Nicopress sleeves than I
really cared to know.
With a magnifying hood, I looked down the barrel of the copper
sleeve that failed on my airplane and there was zero corrosion in
there, nor did I see any on the cable end that pulled through. So I
am convinced that my particular failure had nothing to do with
corrosion, but was solely due to my using the wrong crimp tool. I am
also convinced that plain copper sleeves work just fine with the SS
cables. Several knowledgeable people have advised me "The plating
just doesn't matter", and they're probably right.
There may be considerations other than corrosion due to dissimilar
metals in contact with each other, but I have to think that the
purpose of using one plating or another is to prevent galvanic
(electrochemical) corrosion. I'm definitely not an expert in that
field. but I do have a friend who is a retired chemical engineer.
The two of us went over the Galvanic
Table and agreed that bare copper is the most compatible to
non-passivated 304 (active) stainless steel, followed closely by tin
plate. The zinc plate was very anodic and just looking at that
chart, one would say zinc wasn't a good choice. Go figure...
Yesterday, based upon our research, I was all set to just use the
plain copper crimp sleeves as sold by Lancair. But then I read FAR
43.13(a) (methods, techniques, and practices), which states:
…each person performing maintenance, alteration,
or preventive maintenance on an aircraft, engine, propeller, or
appliance shall use the methods, techniques, and practices prescribed
in the current manufacturer's maintenance manual or
Instructions for Continued Airworthiness prepared
by its manufacturer, or other methods, techniques, or practices
acceptable to the Administrator….
The manufacturer - Nicopress - specifies tin-plated sleeves for use
on stainless cables. So does Mil-Spec MS51844E (SLEEVE, SWAGING-WIRE
ROPE). So does Kitplanes magazine. So does JR Clancy - a rigging
company. So although theoretically the plain copper may be just as
good or better, I have to go with what the "authorities" recommend.
I guess my years working for NASA ruined me...
So I just bit the bullet and ordered 250 (minimum order) of the
428-3-VG Nicopress tin plated sleeves and am having them shipped
from Burbank via UPS 2nd Day Air. Cost: $57 for the parts and $40
for the shipping. Sigh...
I suppose I can sell the unused ones on eBay or something...
Now that I'm in possession of the proper crimp tool that Tom loaned
me, as well as the Go gauge, I've made a couple of test crimps and
they came out just fine. So I'm moving on to some other puzzle
now...
--John
P.S. Another thing I discovered while researching this is that the
FAA is frowning upon the use of stainless control cables at all.
Both of these are kind of funny,
since zinc plated sleeves have been used in the marine industry
for at least the last 40 years, and they hold up pretty (read:
very) well in a salt water environment, up to the strength of
stainless 7x19 cable.
Guy Buchanan
Ramona, CA
Kitfox IV-1200 / 912-S / Warp 3cs / 500 hrs. and grounded
Now a glider pilot, too.
On 7/20/2014 5:26 AM, John Cooper wrote:
or zinc-plated sleeves are used on galvanized carbon steel cable.
Tin-plated sleeves (or as noted previously, stainless
steel sleeves) are used on stainless cable. There are no
exceptions.
and...
Zinc-plated sleeves on stainless
cable has been an obsolete recommendation for
more than 40 years.
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