How to Make a Quality Crimped Joint

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Whilst understood well within professional harness makers, the correct application of crimps is something that doesn’t seem to be as widely understood in DIY circles with much information available ranging from not very thorough to out-rightly wrong; One of my friends was once given the advice by an employee in a car hi-fi shop to hold the crimp onto the cable with insulating tape and nothing else....... Crimping is a technique that can produce reliable, long lasting joint, efficiently and easily with very little training.

There are a vast range of crimps out there in the market- industrial users of crimps have good access to information from the crimp and tooling manufacturers so I won’t go into depth on these applications. Instead, in this Instructable I hope to give some advice on using crimps that you are likely to encounter in installing accessories or making repairs to your car, boat or caravan or in projects at home.

Much of this Instructable will focus on materials and tools, so I will split this down into detail in three main areas and will keep the introduction materials simple:

Materials

Good quality crimp terminals to suit the application

Stranded wire of a known specification (not solid core)

Heatshrink

Tools

Good quality wire strippers

Crimp tool to suit the terminals

Step 1: Choosing the Wire

Choosing the Wire

Depending on your application, you may or may not have a choice on the wire to use. Firstly do not use solid cored wire, and if you want a reliable job heavily avoid ‘conduit wire’ (a few largish strands intended for mains buried in conduit). Specific types of crimps are required to use this type of wire reliably. The best wire for general use will be one with many strands.

Next determine the wire size- This may be listed in a number of ways, the most common being AWG (American Wire Gauge)(e.g. 16AWG), Cross sectional area in square mm (e.g. 1sqmm) or strand and diameter count (e.g. 32/0.2). There are plenty of tables around to help you convert between common sizes.

If buying new wire, the size will be listed on the reel or packet. If modifying an existing installation it may be more difficult to determine. Many wires are now either printed or moulded into the insulation with this information repeated along the length so it will be work a look to see if you can find it.

If you can’t find this information you will have to fall back to measurement and a bit of calculation. Strip back a length of the insulation and then count the number of individual wire strands and measure the diameter of one with a micrometer or vernier calliper. You can then cross refer to a table or calculate the cross sectional area by multiplying the number of strands by the area of one strand calculated by πr2.

Insulation diameter is important for the most reliable crimps as it affects how the rear of the crimp grips the wire, however as long as you use standard wires, then this should not give you a significant issue. It is however important to consider this is you are using a crimp in a professional application.

Step 2: Choosing the Crimp Terminal

Choosing the Crimp Terminal

Now you know what wire size you have, you will also need to work out what you need to connect to. There are many, many variations of crimp, but there are a handful of very common ones, most shown in the image. Crimps designed to fit to threaded fasteners can be simply specified by the bolt size (e.g M4/ ¼”). Others may have different names dependent on the industry and manufacturer (eg lucar, faston, ¼” blade). Critical to getting a good joint will be the quality of the crimp- it is difficult to get a good, long lasting joint with a poor quality crimp terminal.

Plating
Terminals are available with a number of different plating options to give corrosion protection and for other technical reasons (such as low contact resistance). I would avoid any crimp (if at all possible) that doesn’t have a plating so that you don’t have to re-visit it in the future to clean it of corrosion. This will be especially important in the more corrosive atmosphere like those found on a boat. The most common available plating is tin, and this will be suitable for most needs. Silver and gold are also common in certain applications, but are usually used in low current/ signal applications where a minimum resistance across the joint is needed.

Pre Insulated Crimps
If using pre-insulated terminals the better quality connectors have a metal sleeve to grip the wire insulation, the lower quality parts don’t have this. The image of the sectioned crimps shown make this obvious, but to determine this when not sectioned, look down the barrel of the crimp from the wire entry end. You will see metal to almost the end of the crimp in a quality part, but it will stop short in cheaper parts.

All terminals will be sold with a defined wire size range- this should be listed on the packet, but if not and you are using pre-insulated parts you can tell by the colour of the sleeve. The generally adopted standard is:

Red Insulation 0.5-1.5mm2 / 22-16 AWG

Blue Insulation 1.5-2.5mm2 / 16-14 AWG

Yellow Insulation 4.0-6.0mm2 / 12-10 AWG

There are other colours around, but you are unlikely to come across these unless you are doing industrial, aerospace or military work.

Closed Barrel Un-insulated Crimps
These parts are made in one of two ways- sheet formed or tube terminals. The sheet formed ones are manufactured by cutting the material out of flat sheet and then shaping to make a tube on one end. Better quality ones of this type will have thicker material and the seam brazed. Tube terminals are manufactured by cutting a piece tube to length, flattening one end and punching a hole. The tube type tend to be heavier duty and therefore are more common in the larger sizes- for example you might encounter these on a starter motor feed.

Open Barrel Un-insulated Crimps
This type of crimp has by far the biggest amount of variation tending to be the type used in connector housings. Of the many thousands available, by far the most common that you are likely to come across are of the blade type, of these the ¼” blade are the most common with 1/8” (3.2mm) and 3/16” (4.8mm) also frequently encountered. You will find these connectors widely used in cars, domestic appliances, Hi-Fi equipment etc.

You may well find different types on your car for other applications- if you need to replace these good auto-electrical suppliers can often provide you with a kit of parts. These types will often need a very specific tool to crimp correctly.

Turned Pin
These are most commonly encountered in military-spec connectors, but may also be encountered in industrial connectors, RF connectors and high quality D-Types. They are manufactured by turning parts from rod and hence are almost invariably round.

Other Types
There are many other types of crimp around, most of which have specific applications and you are therefore unlikely to encounter in day to day life.

Packaging
A large proportion of crimps are available in a form that enables automatic crimping on a specialist machines- normally a strip or carrier supplied on a reel. These can be crimped with hand tools, but will need to be removed or cut from a carrier strip. Other terminals are supplied as ‘loose piece’- individual parts supplied usually in bags or boxes.

Step 3: Choosing a Tool

Choosing a tool

As with any other tool, there are a wide variety of options available, covering a huge range of price and quality. A cheap generic tool may start at £2 with good quality, calibrated hand tools often exceeding £400 and automated equipment running into tens of thousands of pounds or more.

As a general rule, I would try and avoid any tool that doesn’t have a ratchet feature- although sometimes this is just not possible, it is best to make the choice knowing why.

Pliers type tools rarely have any method of ensuring that a crimp is correctly consolidated- a ratchet tool will have. You can therefore guarantee that a crimp has been correctly formed (if you have selected the correct crimp and wire for the die). Similarly hammer type tools have the same issue.  More about this later.

To get the best results the tool should be selected to suit the terminal- the best way to do this would be to buy the manufacturer’s recommended tool for every crimp you use, however this isn’t likely to be practical for the DIYer for obvious reasons. Manufacturer’s datasheets will generally list the part number of the correct tool. For the most common crimps, there are generic tools available at reasonable prices which will work suitably well. In reality there are a very limited number of manufacturers of these tools in the world, so if you buy a cheap, basic tool the chances are it will be the same part. The main manufacturer of these is a company called OPT in Taiwan- http://www.opttools.com/ . From personal experience these are good functional tools for the insulated terminals, blade terminals and un-insulated closed barrel terminals, and are available at reasonable prices.

The other main manufacturers of hand tools for the big crimp suppliers I am aware of are:
http://www.wezag.de/index.php?lang=en_US
http://www.pressmaster.com/
http://www.rostratool.com/
http://www.dmctools.com/
http://www.astrotool.com/

These do all sell under their own name as well as ‘badge engineering’ for others. You will however have to go to a dealer/ distributor to purchase their parts as they all only sell to the trade.

Step 4: Making the Crimp

Making the crimp

If you are using an un-insulated crimp and need to sleeve it, put a suitable piece of sleeving onto the wire. Typically 3:1 shrink ratio, adhesive lined heat shrink would ensure that good support of both the wire and crimp is made. A length at least 2 times the crimp barrel will usually give a good grip. Other sleeving can be used- in particular neoprene sleeves (Hellermann Sleeves) also work well.

Before carrying out a lot of crimps, it is probably worth doing a test crimp on representative wire and terminals to ensure you have settings correct.

Once you have determined the length of the wire is to strip the end, being careful not to damage the conductors. The length to strip may be stated on the packaging of the crimp, but if not should be so that when the wire is inserted in the crimp, 1-2mm extends out from it. Insert the wire into the crimp, making sure all strands are in, and none are left straying. It is not recommended to twist the strands together.

Carefully place the crimp in the wire in to the tool (you may find it easier to put the crimp into the tool prior to the wire with some crimps), and ensure the wire is seated home. Cycle the tool- if a ratchet tool, until the tool releases. Remove and inspect the crimp- ensure that the wire is in the correct position, and the insulation is gripped successfully. Give a small tug to ensure fully crimped.

If you are using some of the cheaper/ non-ratchet tools, you may have to crimp each terminal twice, possibly with two settings on the tool. If you need to do this, crimp the conductor end of the crimp first, followed by the insulation.

If using heatshrink, or other sleeving. Fit the sleeve and if necessary heat to shrink down. Use a suitable heat source- ideally a hot air gun, but items such as soldering irons can be used with a lot of care. Before shrinking, make sure the sleeving is in the correct place, not obstructing the terminal end of the crimp.


Step 5: Further Information

Further Information
Some Science & quality Control


It is both possible to over and under crimp a terminal;

Crimp systems are designed to compact the wire strands together to a set level so that no interstitial spaces (gaps) are left between the strands. This stops both moisture and oxygen entering the crimp and therefore prevents corrosion from occurring.  If this is correctly carried out, soldering the rear of a crimp (as some people will recommend) will have no effect on the corrosion resistance of the joint as there will be no space for the solder to enter. Ultimately the crimp process aims to deform the wire and crimp to a preset level, to eliminate the spaces as well as cold work the wire to a pre-determined level.

Under-crimping which can be achieved by using the wrong tool or die for the crimp, not cycling the tool to fully closed, using pliers type tools or by incorrect selection of crimp and wire, will leave these interstitial spaces open, allowing moisture and oxygen to enter, ultimately allowing corrosion and hence a high resistance joint, or mechanical failure. If under-crimped, the joint will also have reduced mechanical strength, and at an extreme level will pull out with very low force. Whilst the pull strength of the joint isn’t an ideal test (due to over-crimping issues described next), it is a common test that is quick to apply in a factory environment and is hence commonly used as a quality control check.

Over crimping of the joint can have equally disastrous results- at an extreme level, the imposed stress on the wires can lead to complete failure, which is likely to be obvious. A less obvious issue is a greater sensitivity to fatigue, which will occur in places with vibration where the failure may not become apparent for some time. This type of failure is analogous to what happens when you keep flexing a paperclip- the material work hardens and then eventually fails. Over crimping is more difficult to detect as a simple pull test won’t necessarily pick up the issue, due to this other quality control techniques tend to be used, although none of these are practical for the DIYer;

Microsectioning- this is a destructive test that is the only completely definitive method of determining the quality of a crimp- It is therefore often used in industry to ensure the design/ calibration and set up of crimp machinery is correct, where samples can be taken and analysed. The process consists of cutting a crimped joint through the crimped area, mounting and polishing the section and inspection and measurement with a microscope. The criteria for a good joint are mostly to determine if correct consolidation has occurred- i.e no void spaces, no inclusions of foreign matter or oxides and approximately hexagonal sections of the crimped wire strands.

Pull tests- by hand this can be a gentle tug on a joint, but in a production environment a calibrated tester is usually used to apply a force until the joint fails, noting the yield force achieved. This can be a quick in-process check which will detect under-crimping, but not necessarily over-crimping.

Crimp height- measurement of the height of the terminated wire in the crimp area is a good method for quality control as it is non-destructive, and can pick up both over and under crimping simply.

Crimp force- many automated crimp tools measure the force applied during the crimping process. This is another reliable method of getting an indication of crimp quality, and has the advantage that it is an in process check- no need to stop machines or remove samples.

Soldering- you may see recommendations to solder crimps elsewhere. There is absolutely no need to solder any crimp. In fact you may reduce the reliability of the crimp by doing so. Crimps are designed to control the flexure of cable at the entry point. Soldering can stiffen the joint and result in premature failure.

Esoteric tools- Due to the dangers of over-crimping described above, and the difficulty of detecting it, I would strongly advise against using a hammer type tool, or anything else that is not specifically designed for the type of crimp. This includes squeezing in a vice, squeezing with a vice with a nail to indent, using ground pliers, whacking it with a hammer or any other brutal method that might come to mind. You might get a reasonable result, but there is a very high risk you won’t and the joint will fail prematurely.

Further Reading
Unfortunately there is very little widely available information on crimp technology, and by far the best book is currently out of print;

Electric Connector Handbook: Technology and Applications (Electronic Packaging and Interconnection Series), Robert S Mroczkowski, ISBN 978-0070414013

Most of the major crimp manufacturers do however produce some sort of guide, the following are good examples. Others are available;

http://tooling.te.com/pdf/US_crimpposter.pdf
http://tooling.te.com/europe/pdf/crimp-connections-english-german-3-1773444-1.pdf
http://www.molex.com/pdm_docs/ats/TM-638000029.pdf
http://www.molex.com/pdm_docs/ats/TM-640160065.pdf

Step 6: Top Tips

Top Tips

Finally, my top tips for a sound, reliable crimped joint are;

Buy good quality crimp terminals
Match the right crimp to the right wire size
Take care when stripping wire not to damage it
Use a good quality ratchet crimping tool
Don’t solder the crimp
Use heat shrink tubing to provide any strain relief or insulation if needed

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    35 Discussions

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    and1hotsauce

    11 months ago

    Hello,

    Great article :)
    For my 3D printer, I'm trying to crimp the three cables of the power cable (neutral, ground and phase). I'm pretty sure that these are 18 awg (I can use the "18 strip section" of my crimping tools without altering the wire strands). I'm pretty sure that my crimp (see the link with images) is pretty poor. Can you confirm ?
    All the strand are grouped in one side of the crimp connector. I have the feeling that the red connector is to big/large for the quantity of wire strands :-s

    The connector seems to hold well on the tire.

    https://photos.app.goo.gl/OM8DQ6j60qOFTdKh1

    Thanks

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    a-morpheusargos090

    Reply 1 year ago

    Here's a nice article on what happens in a crimp joint and why in various cases they're preferable to soldered joints: https://hackaday.com/2017/02/09/good-in-a-pinch-the-physics-of-crimped-connections Plus a nice video which shows what happens in detail to the wires being crimped and other things about crimping.

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    AlanS14argos090

    Reply 3 years ago on Introduction

    Crimps are superior in several ways for many applications not least of which is lower resistance than soldered joints.

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    superpantsargos090

    Reply 6 years ago on Introduction

    There are many reasons why a crimped joint may be used, and indeed may be preferable to a soldered (or indeed screwed joint). The common advantages are:

    Higher reliability of joint in many cases, especially in vibration or high temperature applications.
    No heat involved so safer to use in many cases- especially in confined spaces, or near flammable materials
    Equipment highly portable- especially compared to soldering equipment for larger cables
    No heat damage of insulation possible, or solder wicking up conductor
    A mating half to an existing connector may only be available in crimp style
    Lower level of skills training required for a user to achieve consistent results
    For production users, ease of automation & integration of process controls for quality
    It is easy to correct wiring errors by removal and re-insertion of contacts in a housing

    There will of course be many applications where a soldered joint is preferable, but I hope that this Instructable helps people make an appropriate choice.

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    jimbody59

    1 year ago

    well I read all this, may have learned something, but it lacks the information we really need. All those photos and comments and still it does not show the popular crimp, how its made up, and what tool (shape) that should be used with it.

    The insulated crimp with metal tube and a pip in the middle (wire end stop) is the most popular, and the shape of the crimper would have been nice to see.

    So yet another "heres 50 types" and "these 6 crimpers" that dont tell us anything.

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    lloydrmc

    2 years ago

    Good Instructable.

    I just printed up your color-coding chart to use for a wiring project, as I can never keep them straight.

    1 reply
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    a-morpheus

    2 years ago

    no problem. hm...might I ask your opinion on something? I was just looking to buy a crimper and I haven't quite figured out how to know if any given crimper does the kind of crimps I might want. I want to do some "Dupont" crimps for electric circuits (small, like these http://tinyurl.com/zxaossy) but also sometimes crimp onto larger wires, like mains power cord size wires. I was looking at this crimper:
    http://tinyurl.com/hxkju5z
    but then I also see crimpers that say they're specifically for Dupont type:
    http://tinyurl.com/jjl2e9p
    so I'm not sure if I get one that is not specifically for the Dupont crimps if it will work.
    I would use them mostly for micro-controller type circuits and that not every day. I was hoping to find something under $30-40, like either of the ones I linked to. I bought a lot of stuff from that site recently and so far everything has worked well.

    2 replies
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    superpantsa-morpheus

    Reply 2 years ago

    Thanks for the query- I'll start with a bit of background:

    The connectors known as 'Du-Pont' connectors are really a generic term for
    a square pin, 0.1" PCB to wire connection. Compatible parts are now made by a
    wide range of manufacturers, including cheap unbranded parts made in China and
    each one will have subtle differences to other manufacturers. The original parts
    are now made by Amphenol FCI and have gone a through a range of owners; Du-pont
    sold it's connector business to Berg who in turn sold out to FCI (formerly
    called Framatome), who in turn were recently bought out by Amphenol.....

    The original series are still available- details can be found here:

    http://portal.fciconnect.com/portal/page/portal/fciconnect/producttype?appname=catDisplayByPath$entryPoint=adir%20%20ect$categoryPath=Product%20Type

    Unfortunately due to the now generic nature of the part it's therefore not
    possible to determine a tool that will work with all options reliably. My first
    suggestion would therefore be to buy genuine Amphenol FCI parts through one of
    the catalogue distributors such as Mouser/ Digikey/ RS or Farnell, and track
    down a secondhand Du-pont / Berg tool on Ebay or elsewhere.

    You could try the toll you have linked, and looking at the description it
    will be close, but there will be no guarantee it will work. An alternative to
    try would be a Sargent #3128, again It is a generic tool so won't be
    specifically designed for the parts.

    http://www.sargenttools.com/ToolsByTrade/OPEN_BARREL_CONTACT_CRIMP_TOOL_24_14_AWG/

    Hope this helps!
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    a-morpheussuperpants

    Reply 2 years ago

    Thanks that does help. I am still trying to figure out the crimper world. I found one of these

    http://www.newark.com/te-connectivity-amp/169481-1/hand-tool-for-modu-iv-contacts/dp/93F5678 for less than $50 and am trying to decide if it makes sense to get it...I don't know if it does "Dupont" connectors but I think it might, otherwise it seems to have a rich variety of it's own Dupont-like connectors which I think might offer tighter connections. Any advices on if it's a good, somewhat general-purpose tool to get?

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    a-morpheus

    2 years ago

    I'm not sure what's negative about being good for beginners. I found it an excellent instructable--orgainzed, concise and really helpful to orient oneself, to get a foothold, in the world of crimping. It also gives enough info, I think, that even a beginner has a chance of doing a decent crimp, or at least avoiding a really bad one.

    1 reply
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    AlanS14

    3 years ago on Introduction

    Good for one particular audience - beginners . Too lightweight by far-for almost everyone else, it's a very basic primer at best.

    3 replies
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    JohnW320AlanS14

    Reply 2 years ago

    Alan you seem a rather unpleasant individual.

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    AlanS14superpants

    Reply 3 years ago on Introduction

    It's a subject that can easily fill a book, and has. The best book imho is the out of print one you mention. Why don't you write one?

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    JohnW320

    2 years ago

    very easy to understand. thank you.

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    superpants

    4 years ago on Step 2

    Jim- You are right, thanks for noticing! I have updated the page.