Swaged Studs on Control Cables.
- Thread starter BrianW
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As a general rule, IIRC, a properly swaged cable fitting supposedly equals or exceeds the strength of the cable.
TFF
Well-Known Member
That is why it takes a $5,000-10000 tool to swage to the cable.
BrianW
Well-Known Member
pictsidhe
Well-Known Member
pictsidhe
Well-Known Member
Aircraft spruce offer a swaging service...
Yeah, no. That's a crimper, not a swager. It's only to be used on Nicopress-type crimping sleeves; usually copper or aluminum. For the stainless steel fittings they use on Cessnas and other production aircraft, what you need is a Kearney style swager like the one pictsidhe posted about.
There have been a couple fatal accidents in homebuilts involving improperly swaged cables where they used a crimper instead of the proper swager.
pictsidhe
Well-Known Member
Did Peter ever have his crimped swage fittings fixed?
The swaged terminals do indeed exceed the cable strength. And concerning the "proper" tooling, the machine used to do the control cables on the U-2 today (yes, it's mostly cable), is about the size of a VW Beetle and was used on the P-38 production line in Burbank.
It is a SERIOUS process that requires SERIOUS tooling.
It is a SERIOUS process that requires SERIOUS tooling.
Yeah, I wonder about that too. I know that Marc raised the issue with Wasabi, but I never heard one way or the other.
pictsidhe
Well-Known Member
Darwin must nearly have a full house now.
pictsidhe
Well-Known Member
Why so serious?
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BrianW
Well-Known Member
Ah yes - the manual roll die swager - less force involved, but a nice continuous shrink in the usual two pass arrangement to iron out the crease - which is not an issue in the fancier rotary swager. Trouble is the Kearney does leave a longitudinal crease, which as you may know is the WEAK axis of a cylinder in compression. I was interested to find that some Kearney users like to seal the interface with a 5200 style caulk.
I am having REAL difficulty finding the pull-out strength of roll-die OR rotary swaged terminals. I seem to recall (via my always fallible memory) that the Nicopress style swage is good for 90% of the cable absolute strength - but even that datum is proving elusive.
Regards
Brian W
I've tensile tested several Nicopress cable assemblies. In all cases, the cables broke, leaving the crimps and eyes intact.
Marc Zeitlin
Exalted Grand Poobah
See MIL-SPEC 51844E. It states:
Nominal breaking strength. Eye splices, when properly assembled using the manufacturer’s recommended tools and splicing instructions and when pulled with increasing tension, shall hold until wire rope breaks. It is preferred that tensile loads at failure be not less than 90 percent of the breaking strength specified in table I
So, the design is for 100% of wire rope strength, which the splice "shall" hold. But (and who knows what this means) the "preferred" load at failure is not less than 90%, but there doesn't seem to be a "required" minimum, strangely. "Preferred"? Who wrote this - Bartleby the Scrivener?
BrianW
Well-Known Member
Good Lord! A manual roll swager for $13 grand plus! I would have thought an electric roll drive would have been appropriate at that price. Sooner or later, someone who speaks Mandarin is going to see this.
A serviceable one can be found on eBay occasionally for under $2K. New certified dies were in the range of $450 (per size) last I checked.
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If there were a market for a homebuilder* version that would only roll 3 or 4 of the most used die profiles in the $500 range than it would probably already have been done....electric drive option for another $100.
* even including sail boat owners I just don't see the needed market volume.
BrianW
Well-Known Member
This is an interesting post on several levels.
1) it deals with eyes , not stops.
2) It begs the question, "Where exactly did these cables break?
You know as well as I do, that a terminal stronger than the cable will break at random positions when over-stressed.
I suspect, without knowing for sure, that the wire breaks would be close to the terminal - a feature of any abrupt cross section change; but I would expect this failure mode to be exaggerated in the rotary swage terminal, where the cable compression begins at the very end of the terminal and continue with the cable extension associated with the barrel extrusion towards its end; less so with the roll swage which begins at the end and extrudes barrel, allowing the cable to retreat to the cable side.
In this regard, the Nicopress seems to offer advantages; the swage is localised and allows cable relaxation IF the first squeeze is central and the subsequent squeezes trap the ends (possibly?) but some lateral movement of the terminal meets a soft barrier rather than the hardened steel collar at the wire side of the cable.
But this has its limits:
The Loehle wheel suspension comprises two telescoping tubes with lateral bolts upon which bungee cord is tight-wrapped. Over-extension is stopped with a short restraining cable mounted internally. Simple, and quite effective. This puts two eyes swaged with Nicopress fittings into varying bending loads, Fatigue failure of the wire is inevitable at the swage, sooner or later.
A terminal much used in sailboats is the screwed compression chuck and cone end insert.
It looks like a roller or rotary swage, but is apparently more chancy.
I expect there are more methods - such as the 'hot pour' approach, which fills the interior of a terminal with an end-cone full of lead alloy for instance.
And so I suppose I should end with the Eddystone lighthouse. This was perched on sea-washed rocks and tended to depart in high heavy seas. Until that happy day, when anchor-bolt holes were drilled into the rock, and studs were placed after pouring the hole with hot wax, and setting them with molten lead. These fittings held up against the worst of 50 foot waves in storm surges for many years.
Brian W
The one I remember at A&P school was a big pneumatic one that hammered two female dies together around the swage with about the same force (and noise!!!) as a jackhammer. There was no "rolling" or smooth peaceful pleasant squeezing. It was a violent and dangerous process, the instructors were terrified that we would swage our hands and fingers off!
BrianW
Well-Known Member
Sadly, this has the ring of truth. Pity one has to settle for the Socialist approach to scarce resources - sharing for a fee; rather than the sturdy individualist (Capitalist?) approach of buying an example for sole use. <g>
Brian W
