How to Make A Quality Crimped Joint

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.

Comments

[Technosteve]

twisting the wire will cause crimp faliure and can do so by nearly 60% in some tests during calibration testing using hellerman crimps and tools.

The correct colour crimp tool is thefore paramount to a good crimped connection.
The manual crimp tool that indents the crimp and is usually found as a kit in car parts places those without a ratchet will quicly fail as the insulation will return to its former shape and can slide off the crimp, they can also deform the crimp badly leading to cable faliure usually as a result of over crimping.

I would recommend always using the ratchet type as shown in the pictures.

When looking at the closed crimpers you will see one side is slightly larger then the other this is the insulation side of the cimper and the smaller deforms the metal part of the crimp with this type the insulation does not relax as much over time.

a good instructable none the less.

[argos090]

Can I ask why not just solder wire with a $10(or less) butane torch?

[superpants]

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.

[dchall8]

It seems I could follow your Instructable and still do it wrong. You go into mind numbing detail all the way up until you finally stick the crimp fitting into the tool. It seems to me that the only thing that matters, assuming you are somewhat close in mating the wire to the fitting, is the part you were vague about. Which way do you put it in? Is there a right way and a wrong way? Does it matter if the fitting is sideways or upside down?

It looks like there are many ways to make a crimp, at least by looking at the last picture. Is the same tool used for all of them?

[superpants]

Thanks for taking the time to comment. One of my aims in writing this Instructable was to make it clear that there is far more to making a reliable crimp than often thought- I’m therefore disappointed that this is seen as ‘mind numbing detail’. On re-reading that section, I can see that I do need to expand it a little to ensure orientation & cavity size is properly covered and will do so.

I have earlier in the Instructable indicated that the correct tool for the crimp needs to be selected to suit the crimp- so no, the same tool cannot be used for all of them.

[pcooper2]

A properly executed crimp joint will be mechanically and electrically more reliable than a soldered joint. The key to an acceptable crimp joint is that it must be "gas tight" -- the metal of the wire and the crimp lug are pressed so intimately together that if it were the lid of food can, it would be an hermetic seal. To get the best joint, the crimp lug should be matched closely to the wire gauge: The stripped wire should just slip into the lug with minimal side-to-side play. The crimping tool is important as well, as the most inexpensive tools found in automotive supply stores tend to crush the crimp lug and not properly compress it around the wire. Unfortunately, industrial crimping tools can be quite expensive, costing hundreds of dollars apiece, and one may need several different tools for different sizes and styles of lugs and terminals.

Avoid cheap knock-off crimp lugs from China and other moderately disreputable places, especially if they are to be used in automotive or aviation applications. The brand-name lugs and terminals from western European and North American suppliers will cost more, but are worth it in the long run by avoiding joint failures later.

[pecker]

Excellent instructable.
I'd agree! Buy a ratchet crimper.The cheap "squeeze and pray" type of crimper will either chew your terminal, leave bare wire exposed or not grip properly.

[superpants]

Thanks a lot for the kind comment facklere, senorbutt & pecker!

[magickaldan]

Your suppose to put the dimple of your crimp tool on the opposite side of the seam on a crimp connector. Unless the seam is brazed then it doesn't matter what orientation you put the crimp tool on.

[superpants]

Absolutely right- In the example in the photo this is a brazed seam crimp, wher I wanted to show the indent.

[facklere]

Excellently written and illustrated. This topic was always a bit foggy to me, but now I feel like I have a good beginner's knowledge. Thanks!

[senorbutt]

Very well written and informative, thanks!