Crimping Jumper Wires

[TerryJC]

Updated Procedure (2) - Having discovered how to load the crimp-pot into our tool (see my posting of a few weeks ago viewtopic.php?f=15&t=114#p2370) and done another few hundred crimps, I think I have finally worked out the most efficient way to do this. The details of most of this have been posted before, but to make it easier, I have edited this post to provide the full instructions for our tool. I originally posted this because of the number of crimps that we (and future WMT volunteers) are going to have to do and because I found it quite a marathon to find out exactly how to do it. However, I've now run the marathon, so others don't need to.

The nature of the I/O Pins on the Raspberry Pi and its peripheral electronic modules necessitates the use of contacts of the type known as DuPont Header Pins. Once connected they are quite reliable, providing that good quality contacts are purchased and they aren't removed and replaced too many times (we're talking hundreds here, not tens). It turns out that of the two batches of contacts that we purchase on; the boxed set is definitely NOT good quality and the other batch are OKish.

The jumper wires can be bought pre-made up from various sources, eg

Jumpers.png (49.98 KiB) Viewed 1526 times

but they tend to be a bit restricted; only one size and you have to buy three types to get every combination of ends.

The answer is to buy one or two types (female to female and male to female), then cut them to length and crimp or solder the other end. (Soldering can be difficult because some types of Jumper use wire that has a poor affinity to solder.)

Various companies supply these tools, but the proper DuPont tool is extremely expensive, so alternative suppliers provide what are usually Chinese copies and some even provide online tutorials to help their customers to use the tool. Our tool however, was not sourced from such a supplier and in fact it seems to be significantly different to the 'proper' tool in one respect; it is handed the opposite way round.

Here is the way to do it with our tool:

1. Prepare each wire by cutting it to length and stripping approximately 2 to 4 mm of the insulation. It's important that the wire doesn't protrude into the mating area of the contact in step 6 below to prevent fouling when trying to insert the contact into the shroud.
2. Using a pair of snipe-nosed pliers, lightly nip the insulation tabs to allow the contact to fit snugly into the first position on the tool. (This is because our tool is slightly wrong for the contacts that we've bought.)
3. Hold the tool with the jaws to the left and the moving handle away from you (see picture below).
4. Place the contact into the jaws of the tool. Align the closest leaf of the insulation tab in line with the near face of the jaws and close the handles until the contact is held snugly, but not compressed.
5. Carefully slide the wire end into the contact until the insulation butts up against the inner step in the crimping jaws. This marks the bginning of the wire crimping area. If the previous step has been done correctly, then the wire will be positioned perfectly.
6. Crimp the contact fully and withdraw the assembly from the tool.
7. Examine the job to ensure that the insulation tabs have crimped exactly to the end of the insulation and the wire is crimped tightly.
8. Using the snipe nosed pliers carefully squeeze the crimp around the insulation so that the tabs almost meet and the contact slips easily into the shroud in the next step.
9. Carefully slide the contact into the plastic shroud with the opening uppermost and the contact matching as shown below. (Our contacts appear to be slightly over-size for the shrouds, making it difficult to get the contact to click into place. To avoid the contact being pushed out of the shroud it is essential that the contact is fully home.)

Notes:

• Use the pre-made wires to ensure that one end is 'good'. Solder the other end if possible, eg to the Veroboard or DC / DC Converter.
• Where crimping contacts is unavoidable, eg the Pi, the A/D Converter and the Motor Drive Board logic inputs, gang them together using multi-way shrouds to help retention and ensure that the contacts are pushed fully home in the shroud.

Holding the Tool:

Holding_the_Tool.jpg (354.64 KiB) Viewed 1486 times

Loading the Contact

Contact_Loading.jpg (235.54 KiB) Viewed 1486 times

Fitting the Shroud

Fitting_Shroud.jpg (318.4 KiB) Viewed 1486 times

Use pre-made wires cut to length as much as possible.
[*]Solder the other end if possible, eg to the Veroboard or DC / DC Converter.
[*]Where crimping contacts is unavoidable, eg the Pi, the A/D Converter and the Motor Drive Board logic inputs, gang, them together using multi-way shrouds to help retention and ensure that the contacts are pushed fully home in the shroud.

[TerryJC]

A quick word of caution. You need to read the information in the link as well as watching the video, as I've just found out to my cost. In the video the guy says that you don't want to crimp the insulation, but in the words it says that you do. It goes without saying that the insulation needs to be crimped otherwise the contact isn't held properly and will not seat correctly in the plastic shroud.

Unfortunately, I did it right when I originally tried this nearly a week ago, but when I set out to make up a lot of leads, I viewed the video to remind me and forgot exactly what the words had said.

It's obvious really when you think about it, but unfortunately, when you've made up a load of wires and they all fall apart when you are trying to insert them onto the header pins....

[Penri]

How frustrating, do you need me to lend a hand?

[TerryJC]

It would help, except that I'm trying to document the length of the wires as I go along. To do that, you'd need the partially assembled baseboard. Shall we discuss it tomorrow? I'll be able to do some work when I return from the supermarket tomorrow morning. Once the lengths and ends are specified it should be relatively straightforward to make up a full set of leads (albeit time consuming).

After the leads are manufactured and commissioned, I'll still need to complete the software before we can use the assembly.

I'll bring everything in with me so you can see what I'm trying to do.

[TerryJC]

Not wishing to blame my tools.... but I've found that when the contact is placed into the jaws of the crimping tool it is very difficult to get it in because the insulation tabs on the contact are too wide for the jaws in the tool (I'm using the first position as in the demonstration). This can be overcome by closing the tabs slightly using a pair of pliers, but the tabs may then be too narrow to push the insulation in!

Furthermore, When I get the wire in properly, the insulation is crimped extremely well, but the important part; the wire core, isn't crimped at all. I'm not sure if the version of the tool that we have is an imperfect copy (it's certainly a copy), or if it's the contacts are an imperfect copy. I have ordered a couple of hundred female contacts from eBay and these are sold as 'DuPont' (they may still be a 'Chinese Copy', but maybe they will be a better fit for the tool.

In the meantime, here is what I've found to be the best approach:

1. Prepare the wire as detailed in the Tutorial referenced above.
2. Using a pair of pliers, lightly nip the insulation tabs to allow the contact to fit snugly into the first position on the tool, as per the tutorial.
3. Place the contact into the jaws of the tool, taking care not to put it too far. (I ended up puttting the closest leaf of the insulation tab, pretty much in line with the near face of the jaws, not 1 mm in as in the tutorial. Either way didn't seem to make much difference.)
4. Carefully slide the wire end into the contact, ensuring that the insulation is past the nearest insulation tab by about 3 - 5 mm but no more.
5. Crimp the contact fully and withdraw the assembly from the tool.
6. Examine the job and if the wire tabs have not been crimped, finish the job with a pair of pliers.

That's it, apart from ensuring that the contact is inserted into the housing with its tongue aligned with the open part of the housing.

[TerryJC]

Ok. The new contacts arrived today and they are virtually identical to the ones in the kit that you bought Penri. They seem slightly shinier and the metal seems a bit harder, but they don't fit into the tool any better than the ones from the kit. So it looks like the tool may be the problem or I'm simply not loading the contact properly. Either way, the procedure outlined above seems to be the answer.

It makes the job take twice as long, which isn't a major problem, unless you have a lot to do.

[TerryJC]

Having spent several hours yesterday and several more today making pretty unreliable crimps (and therefore having to do them again), I made a discovery.

The fact is that our crimp tool is perfectly suited to the job, but the crimp jaws have been manufactured back-to-front. If you look at the Tutorial linked in my first post (and in particular the YouTube video linked in turn, from the Tutorial), you will see that the contact is loaded into the jaws with the wire side of the contact flush with the face of the jaws on the side where the retaining screw heads are. I was examining the jaws on our tool and it suddenly clicked that they were made with the wider portion of the jaws the opposite way to what would be expected (eg, wide for insulation, narrow for wire). When following the instructions in the video with our tool the insulation was being crimped by the narrow part and the wire core wasn't being crimped at all!

I loaded the contacts from the other side and hey presto; a perfect crimp. It is still necessary to push just the right amount of insulation into the jaws (a fine judgement), but once it is right the crimps work. Once made they are quite stiff to push into the housings, but that's got to be a good thing.

The pictures below show how it should be done:

Wire Side (you can see the ends of the securing screws):

Crimp_Tool_Contact_Loaded_Wire_Side.jpg (262.84 KiB) Viewed 1491 times

Connector Side (you can see the heads of the securing screws):

Crimp_Tool_Contact_Loaded_Connector_Side.jpg (281.09 KiB) Viewed 1491 times

[Penri]

Interesting, I have a similar issue with a ring / spade terminal crimp tool, it works best when you load the crimp and wire on the side without the colour coding which tells you which jaw to use. Must be a conspiracy!

[TerryJC]

Perhaps Chinese wiremen are all left-handed. It feels cack-handed to load the contact upside-down.

Works though. I'm now around half-way through crimping all the wires for five Gate Valves. It should be a lot quicker when I start the other half.

[TerryJC]

Over the past week or so I have learned quite a bit about our 'Chinese Copy' crimping tool, contacts and shrouds. These points should be borne in mind when crimping:

1. The crimp contacts in the box that Penri bought, with assorted shrouds and both male and female contacts, are made with very soft metal and cannot be relied on to be retained on the pin, especially if they are removed a few times. Do not use these contacts at all!
2. The shrouds in that box seem to be OK within limits (see below).
3. The male contacts that I bought in a reel of 250 with single shrouds seem to be OK, except that the contacts are quite difficult to push into the shrouds (this applies to the assorted shrouds as well). This has to be watched, because if the contact does not 'click' into place it can be pushed out of the shroud when it is pushed over the pin with a strong possibility that the continuity is broken.
4. So far! the made-up female to female ribbon sets that I bought seem to be OK; the contact is retained adequately by the shroud, and they are easy to extract and push in.

To combat these problems:

• Use pre-made wires cut to length as much as possible.
• Solder the other end if possible, eg to the Veroboard or DC / DC Converter.
• Where crimping contacts is unavoidable, eg the Pi, the A/D Converter and the Motor Drive Board logic inputs, gang, them together using multi-way shrouds to help retention and ensure that the contacts are pushed fully home in the shroud.

I will update the procedure in the first post of this topic to reflect these findings.