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Old 18th Sep 2018, 11:37 am   #1
'LIVEWIRE?'
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Exclamation How are screened leads made?

I was prompted to ask this question when someone yesterday commented on the very thin twin screened lead in a pair of headphones. At the time I was soldering the connections back to one of the two earpieces (not a job I would want to do frequently, b.t.w.!) Obviously all screened cables (and all other wires for that matter) are machine made, but until that moment I'd never thought about the detailed process involved or seen an explanation of it anywhere.
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Old 18th Sep 2018, 12:41 pm   #2
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Default Re: How are screened leads made?

On a braiding machine. The only place I have ever seen them is many (30+) years ago I went around the Rists factory, somewhere around the Potteries if I remember correctly. The cable to be braided goes down the middle, and all the reels of braiding wire wizz around the grooves on a horizontal plate, thus weaving the braid onto the cable travelling slowly through the middle. The clever bit is that half the bobbins go one way, and the others go the other way, but they never meet. Fascinating to watch; a clever bloke who invented it.

Apparently Rists used to have dozens of them, but by the time I went there they only had a few remaining
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Old 18th Sep 2018, 12:46 pm   #3
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Default Re: How are screened leads made?

https://www.youtube.com/watch?v=1D1ZbjKxUIE

If that's to fast watch this:

https://www.youtube.com/watch?v=ded81OdvXSM

Lawrence.
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Old 18th Sep 2018, 12:54 pm   #4
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Default Re: How are screened leads made?

Thanks for the video, Lawrence. Without it I would have been clueless, but now I see it's like children dancing around a Maypole! Ingenious.
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Old 18th Sep 2018, 12:55 pm   #5
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Default Re: How are screened leads made?

I used to go to Rists in Newcastle under Lyme and repair various machines including the braiding machines. On a sunny day when you walked into the braiding shed with its eastlight roof the atmosphere would be twinkling with copper dust.

The previous post is a good explanation, I like to think of it as dancers around a maypole. The bobbins of single strand are grouped in say 3's on a little turntable, then the turntable rotates. Each machine has say 10 turntables of 3 and as they rotate they pass under and over each other. The cable moves along and gets the screen over it. The ones at Rists had the cable vertical, though horizontal ones also exist.

Or you could think of it a bit like one of those orrery things that demonstrates the solar system.

https://www.youtube.com/watch?v=2KfwAkc8Dpo
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Old 18th Sep 2018, 2:03 pm   #6
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Default Re: How are screened leads made?

Thanks Lawrence for link, you have got to admire the Mechanical Design Engineers for all those wonderful machines that have been made over the many years.
Cheers
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Old 18th Sep 2018, 2:13 pm   #7
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Default Re: How are screened leads made?

I have seen a Victorian medal ribbon braiding machine in the flesh.
It had a flat gearbox within another gearbox with notches in the wheels shaped so that the supply spools passed from gear to gear.
It is in North Mills museum at Belper Derbys.
They let me rotate it slowly by hand for about a quarter of a turn so that I could see how it works.
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Old 18th Sep 2018, 5:19 pm   #8
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Default Re: How are screened leads made?

Quote:
Originally Posted by trsomian View Post
On a braiding machine. The only place I have ever seen them is many (30+) years ago I went around the Rists factory, somewhere around the Potteries if I remember correctly. The cable to be braided goes down the middle, and all the reels of braiding wire wizz around the grooves on a horizontal plate, thus weaving the braid onto the cable travelling slowly through the middle. The clever bit is that half the bobbins go one way, and the others go the other way, but they never meet. Fascinating to watch; a clever bloke who invented it.
I've seen one working as well, sort of thing I could stand and watch for hours, almost worth getting one in place of the TV.

John
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Old 18th Sep 2018, 8:48 pm   #9
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Default Re: How are screened leads made?

Some of the TV coax I've seen lately looks as though there were only a dozen spools on the machine!

Cheap audio cable usually has all the strands wound in the same direction but presumably, it's made on a similar sort of machine; just with all the spools moving in the same direction instead of crossing over with their neighbours?
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Old 18th Sep 2018, 9:16 pm   #10
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Default Re: How are screened leads made?

The process is the same as is used for making shoelaces!

One version I once saw a film of was producing armoured coax about an inch diameter: as well as the copper braiding thing it also overlaid flat steel strip about half an inch wide, in three 'laps' two going clockwise and one (interleaved between the clockwise ones) anticlockwise. The result was strong enough that several miles of the stuff could be hauled as a single length through the underground ducts using a hawser and a big winch.
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Old 18th Sep 2018, 10:52 pm   #11
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Default Re: How are screened leads made?

At work we have reels of braid, for putting over special cables and the like, and also for making earth braids and such like. The difference here, is that there is nothing in the centre, but presumably in the braiding machine there is a mandrel that the braid is formed around.

In fact braids like this are quite common, shoe laces are certainly one example. Cables for irons, and if you go back far enough, all manner of things had cotton braided over the outer insulation. Braided ropes, obviously have a similar braid over the central core.

Cable pulling sleeves are basically big braids of steel wires that are fitted over the end of a cable to be pulled into a duct, and the free end is attached quite gently to the cable. The pulling sleeve is attached to the rope, and the act of pulling the rope pulls the braid to a smaller section and it grips the cable to be pulled in; the harder the rope is pulled the tighter it grips.
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Old 18th Sep 2018, 10:57 pm   #12
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Default Re: How are screened leads made?

The plastic variety is quite useful for cable forms too. You just need a sleeve on the ends to prevent fraying. No screening, of course.
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Old 19th Sep 2018, 9:39 am   #13
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Default Re: How are screened leads made?

Another cunning thing to watch is the machine for winding toroids.
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Old 19th Sep 2018, 10:43 am   #14
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Default Re: How are screened leads made?

One of our companies was Times Microwave Cables Inc in Wallingford, Connecticut, a substantial manufacturer of co-ax cable, and now part of Amphenol. The factory was full of braiders, many of which had their origin in the textile industry. I was always pleasantly surprised that the machines had so readily transitioned from braiding cotton or wool to copper wire.

The cables manufactured ranged from those connecting the radar antenna on the Apache helicopter through to large volumes for mobile phone base stations. The shield on such 'professional' cables is normally the actual foil round the centre conductor insulation. The purpose of the braid is to maintain flexibility and to make electrical contact between the foil and connector.

Here's a picture of a typical braider:
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Old 19th Sep 2018, 1:34 pm   #15
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Default Re: How are screened leads made?

I've just watched the video and I'm in heaven...….proper mechanical & analogue !!


Ahhhhhhhh.
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