Preparing wires for crimping - would a guide be handy?

nigelmercier

nigelmercier

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I've just prepared some big cables (95mm sq) ready to be crimped. The guy who did the crimps (with a pneumatic press) was surprised that I had managed to do it without losing any of the strands.

Having read Nigel Calder on the subject, and assuming that other readers would follow his guide, it seems that some improvements might be of interest.

When I get home I will have some spare time, so would a guide on this subject be useful?
 
Yes please. I don't trust them, so solder them afterwards, but make an allowance for the increased stiffness of the joint.

It would be nice to hear the proper way to do them.
 
It would be nice to hear the proper way to do them
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CRIMP them.........take the cut lengths of wire and crimp fittings to an auto electrician and smile waving fivers at him....Worked for me in Edinburgh and I m welsh !!!!!

Soldering puts a hard stress raiser making it easy for the joint to fail as I saw on a boat only yesterday where wires were soldered into crimps. If you have to go this route then reduce the bending moment at the solder by covering the crimp with several layers of heatshrink extending down the cable making a tapered cover.
 
Agree totally with Bilgediver. RAF practice is (or was) to crimp larger cables where hydraulic or pneumatic crimpers are used. Smaller cables would be tinned before crimping as the soft solder would deform under less pressure, making a better connection with hand crimps. These are the other things that stick in my mind.

The two big no-no's were nicking the conductor when stripping the insulation - the easiest way I found to do it was to carefully cut part way through the insulation by just rolling against a Stanley knife. You could then twist off the piece of insulation you wanted to remove which also twisted the strands for you without touching them. Check it afterwards to make sure you haven't cut into the strands. That's good for two reasons - you don't get any oils from your fingers on the metal and you don't jabbed by a strand either.

The other big sin when tinning a cable was using too much solder and letting it wick to far up into the cable. It does take a little bit of practice to get it just right on a small cable. A good flux on all parts of metal you're tinning and a very hot iron are the main thing, and then just put enough solder to do the job on the iron and touch the cable to it for a second or two. If you are working outside try and get out of any wind or get some shelter for the work somehow.

Make sure you've cut the wire back far enough to leave clean metal if necessary. Use crimps that either have either heatshrink or a support for the cable built in and make sure that the cable's first support after the crimp is close enough that no weight is being taken by the connection but also that it does not form a stress point itself. Cables should loomed quite tightly together wherever possible using lacing and a blanket stitch but tied off every few feet so it's easier to break into.
 
Hammer type crimper from Ancor works well on larger cable, 1/4 inch dia, 6mm and above .....

No soldering on large cables.....
 
I used to be a MOD approved electrical and electronics inspector and trained people on wiring techniques. In my time, 1976-1987, the approved technique for crimping was:
A. Push protective sleeve (usually heatshrink) over wire end.
B. Strip wire with approved stripper. These were similar to the ones electricians use for stripping the outside insulation from flex.
C. Check for any nicks in the copper from strpping.
D. Place crimp on wire end without twisting or touching the copper.
E. Crimp, using an approved crimp tool.
F. Place protective sleeve over crimp, ensuring it will not be trapped when crimp is fixed to terminal.
Twisting the strands, touching the copper and soldering before or after were all not allowed.
All tools were regularly tested and test crimps were submitted for pull testing with every job.
In my spare time I used to make wiring looms for race cars and, as far as I know, none ever failed.
Allan
 
For stripping wires, get an automatic stripper, see here: http://www.cabletooling.co.uk/default.asp

For cable cutters for the larger cables, i.e. 6mm and above, same place! Also get a ratchet crimper, from the same place. For battery terminals get the larger one illustrated, for normal car wiring crimps, i.e. the yellow/blue/red ones get a ratchet crimper from Maplin or any good automotive spares outlet or see here: http://www.quasarelectronics.com/skytronic/710.278-ratchet-insulated-terminal-crimping-tool.htm.

The flimsy pliers packed with crimp terminal kits are worse than useless, crimping in one place only and often destroying the crimp - don't use them unless in an emergency.

I have to say after 40 years of boating that I never tin wire ends, it inevitably leads to stiff joints and melted insulation and hand crimps never seem to clamp down properly.
 
For the larger sizes I use the correct size lug, and crimp in a vice. I then use adhesive-lined heatshrink.

I haven't had any fail on me (yet). So is there any problem in doing it this way?

John
 
One of the problems with cable strippers is that it can be hard to line up the cable if you only have a little bit of cable to play with. The other one is that the bit of insulation you've stripped off goes flying off somewhere. In an aircraft that's totally unacceptable but it may not be that desirable having rolling around your bilges either.

Intrigued that MOD didn't allow twisting of strands or soldering - the Armed Forces certainly did. In fact you'd fail if you didn't tin small crimps and that practice was throughout my time in - oddly enough 1976 to 1988. Totally agree about touching the metal though. Always a bad idea....
 
Thanks to all. I'll get some proper crimpers. Having realised that the cheapos were rubbish I'd been improvising. Ahem. When soldering I've always left a long anti-vibration ending.

What metal are the terminals made from? Is it stiffer than Copper?
 
I agree that is interesting. Most of the work I did at EMI and Marconi was for the forces. I am not too surprised about the lack of cohesive thinking between the MOD and the services. I have seen many examples of similar things happening. Having said that we did pull tests on crimps which proved that the non-twisted ones were slightly stronger, in particular on angle pulls. We never tested soldered crimps.
Allan
 
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