The (Unnecessary?) Art Of Connector Crimping

The “Completion Backwards Principle” is a method of reasoning through a problem by visualizing the end result and then working your way backwards from that point. The blog post that [Alan Hawse] has recently written about the intricacies of crimping wires for plug connectors is a perfect example of this principle. The end result of his work is the realization that you probably shouldn’t bother crimping your own connectors, but watching him work backwards from that point is still fascinating. It’s also the name of a rock album from the 80’s by The Tubes, but this is not a useful piece of information in regards to electrical wiring.

Of course, sometimes people do silly things. Even though there are pre-crimped wires available online for a pittance, you might still want to do your own. With this in mind, [Alan] has put together an exceptionally detailed and well-research post that gives you all the information you could possibly want to know about crimping what is often erroneously referred to as the “JST connector”.

He starts by showing off some common examples of this connector, which if you’ve ever opened a piece of consumer electronics will be like looking through a High School yearbook. You might not know their names without reading them, but you definitely remember what they look like.

We’re then treated to an array of macro shots showing the scale of the pieces involved. If getting up close and personal with metal bits that are only a few millimeters long is your kind of thing, then you’re really going to love this part.

Finally, the post is wrapped up with a few words about the kind of crimping tools that are available on the market, and then a demonstration of his personal crimping method. While some tools would have you crimp both sets of “wings” at the same time, [Alan] tells us he finds taking them on individually leads to better results in his experience.

If this this little taste has left you hungry for a true feast of hyper-specialized knowledge, be sure to check out the Superconference talk by [Bradley Gawthrop].

54 thoughts on “The (Unnecessary?) Art Of Connector Crimping

    1. Um, no. I’ve had to build wire harnesses for automotive applications and the difference between a generic crimper and application-tooling is unbelievable. Let alone when you start getting into mil-spec stuff. I used to think like you then I had to produce consistent, reliable results over and over and over.

      1. Dito.

        I had a chance on crimping an AMP-Seal connector. The crimping tools for those cost around $200-$300. We obviously didn’t want to pay that much for a one-off thing in a hackerspace, so we tried doing that with generic crimpers. It was a major PITA and the crimp was crap.

        1. I own two application-specific crimpers, but I use enough connectors that I spend a lot of time with a generic crimper as well.

          I’ve learned to never trust generic crimps and almost always solder them after the crimp to be sure. I know that soldering can cause problems in some situations but without solder I can’t be sure generic crimps won’t pull out.

          1. You know these things aren’t about two items, you have the official expensive one, and then dozens of alternatives, and just because one of the alternatives is crap doesn’t mean you can conclude they all are.
            That’s what reviews are for, to find the good ones.

      2. 100 percent correct. We purchased a set of crimpers made exactly for the terminals we were working with, quite expensive, around 100 dollars. Decent but easy to overcrimp, undercrimp. We purchased their 500 dollar set for exact crimp specifications.
        There is more to this than everyone thinks. Long term usage, hundreds of hours under load, poor crimps with cheap crimpers always fail.

          1. You are paying for accuracy and precision. Do you complain that a dollar store tape measure isn’t as accurate as a $300 mitutoyo caliper? The cheapo crimped is your dollar store equivalent and made as quickly and cheaply as possible.

        1. I’m curious. How exactly is this hinged piece of die cut metal magically resistant to imitation and worth five hundred dollars? You can’t just measure the shape of that tool and make the same exact thing more cheaply? Is it made of diamond? That’s just fucking silly, I’m sorry. This sounds like the desperate reasoning of somebody who spent half a grand on a pair of pliers.

          1. Buy both and see for yourself. If you can’t see, feel and demonstrate the difference then get out the wire strippers, twist the connections together and black tape the ends. Congrats, you are a pro car stereo installer now.

          2. It’s all about the tolerances — alignment, shape, and direction of force. I mean you could crimp a spade lug collar with a flat-bladed screwdriver but you won’t get a repeatable product. More complex crimp connectors need more complex tools.

            I agree the “real” ones seem absurdly expensive but to be fair they’ll last a lifetime and so it’s not like the mfr and distributor are going to sell a lot of them, which affects the price too.

    2. It’s not about the crimper but whether you are using the right crimp size. The engineer crimpers are well made and comfortable to use (expensive sure) but it’s a purchase I’ll never have to make again so that upfront cost disappears into never never land.

  1. I wish I had bought a PA-09 Crimper way back when I first got my 3d printer. I had crimped a JST connector for a fan using crappy pliers and eventually it broke causing my MCU on my printrboard to break. I revived the board with a new MCU but I could have saved myself the headache.

  2. Crimping a custom harness for a project is intensely satisfying though, even though I usually do a pretty crummy job. I did do a race car harness with Deutch Autosport connectors once, they had lot to say about how to crimp pins and a very expensive tool to go with their very expensive connectors. It did all go together very well though, but I’m glad I wasn’t the one paying or it.

  3. The argument that you shouldn’t bother crimping is about the same as the argument that you shouldn’t bolher learning to solder: if you invest enough time and money, and never do anything someone hasn’t already prepped for you, you can avoid spending a few hours learning a skill.

    I crimp wire terminals all the time, and for one-off jobs there’s a shortcut that makes it easier: strip about 1/4″ of insulation from the end or the wire, then fold the exposed strands back along the wire. That way both sets of crimp tabs bite on the wire’s insulation, and both also provide contact pressure between the exposed strands and the terminal.

    It’s one of those places where one-off builders can afford to use techniques that don’t scale to mass production.

    1. Not really…

      The argument that Alan makes in the blog post is that when you can buy pre-crimped wires in a wide array of colors and sizes for cheap out of China, crimping them often doesn’t make sense.

      You can’t buy pre-soldered wiring from China, the very nature of hand soldering is effectively custom one-off stuff.

      1. “pre crimped wire for cheap from China” — sort of makes my skin crawl. But honestly this could mean anything from absolute trash to something decent. The answer is “it depends”. I bought a bundle of test leads with alligator clips from China. What a nightmare. Absolute trash for wire with horrible crimps. I rebuilt a number of them using quality wire and soldering and threw the rest out. The last thing you want is intermittent flakey test connectors.

        1. Made in Sweden in the 1890’s.

          It was a mass-produced rip-off of stuff China was making just to unload on the European market because it was too gaudy to sell in their own country. Once Europe stole the process of making it, they killed the Chinese export market.

        2. Years ago Japan was the world capitol of the worst crap a factory could make. Today most of Japanese products are top quality, and being made in Japan is a guarantee of top quality. China also goes this way; If you want to pay crap, you will get a crap. But if you’re willing to invest decent money to have your product manufactured, you have a good chance of finding a contractor you will do the job well. It’s true that most of the junk in the stores comes from china, but so does majority of the high quality products.
          I would not be surprised if in 50 years buying something made in China will guarantee that you’re getting top quality product.

      2. “you can buy pre-crimped wires in a wide array of colors and sizes for cheap out of China”

        Inventory management can be a nuisance though. I use female JST-PH and male/female 0.040″-pin terminals with 24 and 30 gauge wire, and half a dozen colors. That’s 36 combinations before we talk about length, which is an issue if you want terminators at both ends.

        You could spend a fair amount of money and fill several boxes with pre-crimped wire, and have less flexibility than I get from a crimper, a roll of terminals, and a roll of wire.

  4. Unnecessary? Check out the FAA and NASA aerospace standards and think again.

    I have more faith in the durability, repeatability and safety of my own crimps than mass produced ones made by a bored worker in a factory.

    1. That all depends on the factory, there are factories with extremely professional workers who even doing 50000 items will make less errors than an amateur with care and dedication makes doing 20.
      Plus a factory can run tests on them if so inclined, so even NASA would be OK using such items.
      Especially since NASA has some quite huge disastrous failures of their own products in its history. wasting hundreds of millions and killing people sometimes.

      1. doesnt matter on the factory, you are either adding in the human element, which honestly if you are getting hand crimped wires from a factory, its crap, or its machine produced, which can be very good, it can be very bad as well and no one will even know until the end user.

      2. Moron. NASA did not produce any products. They produced specifications for products.
        In the nuclear industry we crimp connectors with calibrated crimpers and the connectors are then inspected by a QC person.

      1. You are correct, at work we are subject to a different, safety-critical regulatory system as our equipment doesn’t fly but can kill people if it malfunctions. And yes, aerospace grade crimps are required too.

        I mentioned NASA because everyone has heard of them. Boring old power plants and mines don’t have the same level of public attention.

  5. This is one of fundamental skills that are disappearing due to modern convenience, apparently… skills like soldering, manufacturing your own PCB’s….. you know…. “ingenuity and craftsmanship” skills.

  6. In the seventies I ran setup on Amp and other crimping machines. Dimensional spec and 3 pull tests later and it was ready to run. Otherwise connection probable problems. You have to test. Some organ designs went gaga with plug in everything, the rat nest all soldering ones are still going strong.

  7. I could use some help with crimping. I use a pair of the Engineer PA-09 shown but after crimping the crimp is usually stuck in the crimper and I am forced to pry it out. Does anyone know if there is some issue with my crimpers or (more likely) something I would be doing wrong?

    1. My guess is you’ve either selected the wrong slot (see the engineer web site for the recommended slot to use for each specific connector), or you are pressing too hard; there’s no need to crush them.

  8. The risk in buying pre-crimped leads from China is that teh crimps may be fine but the wire conductors are undersized.
    The best way to get a good crimp easily is with the correct manufacturer’s tool. They are expensive but guarantee you will get the right crimp. You get what you pay for.
    Universal tools are fiddly to use and often produce poor crimps and/or distort the pin shape, especially on smaller sizes.

  9. I don’t ever intend to do production wiring. What crimped connectors I do need from time to time, I usually make do with the best ‘inexpensive’ crimpers I can find, and if I have any doubts about the crimps, I will feed a little solder into each crimp. With a jig or holder, it’s easy to solder several at once, so the added time isn’t terrible.

    I do use lug crimpers more frequently. I’ve bought some inexpensive controlled-cycle crimpers, and as long as I take the time to adjust them, they consistently create reliable crimps. On one pair I found that the crimping dies had guides that wouldn’t let the dies meet closely enough. It took only a little time with a grinder and a flat file to improve the mating.

  10. What is the technique, so popular on cheap crap, where they take the wire strands and fold them back onto the plastic insulation and crimp the whole mess at once? I’ve seen that from alligator clips test leads all the way up to automotive jumper cables.

    Desinged to fail. Those people should be taken ot and shot.

  11. Crimping is very important, I crimp all my wire connections and they last 10x longer then if I soldered the connectors on

    Also having gone threw 5+ cheap crimpers I have to say it’s worth getting a good pricey set

  12. Related story: Long ago the news found out that people making the US nuclear missiles had to wait so long for approved simple things like resistors that they just went to a local radio-shack (an ancient US electronics parts store) and used those.
    Mind you that was so long ago that the poor quality parts were still made in the USA and you could not blame other countries. Aren’t you glad we live in the enlightened age?

  13. I have had lots of experience with crimped connectors and as a result, a number of failures. I have resisted paying $600 for pliers to crimp Ampseal pins and have produced my own ,that in most cases, will suffice. I took a pair os long nose pliers and drilled a set of holes, 1mm/1.5mm/2mm and 2.5mm in the centre. I place the crimp centre wire receptor into whichever hole suits and close the pliers. Not perfect, but has worked for me.

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