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Practical Wiring - Professional Motorsport: Concentric Twisting

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Concentric Twisting


00:00 - It would be impossible to overstate the amount of time that the concentric twisting process adds to our wiring harness construction but the reliable and professional result it achieves is absolutely worth the investment for a professional motorsport application.
00:15 To demonstrate how the process is completed, we'll look at the single wire harness section that we went through the design process for in the practical design skills section of the course.
00:25 The process begins with building the core of the harness around which the rest of the layers will be laid.
00:31 One of the keys to a tidy concentric twisting job is to keep your work under a small amount of tension as you progress.
00:37 To this end, a pair of temporarily mountable bench vices is a great help.
00:41 The pair that I have here clamp to the edge of the work bench, and although are fairly cheap and lightweight, are robust enough for the job.
00:49 I would avoid suction cup mount vices unless they are a very high quality unit as I've not had good experiences with the cheaper units.
00:57 For our example lay up section, the core is made of four twisted shielded pair cables wound together with a left hand lay.
01:06 The direction of lay is not critically important but it is convention for the final layer of the cable to have a left hand lay.
01:13 This means that a single conductor passes from right to left as it travels over the top of the cable.
01:21 It can also be thought of as a counter clockwise rotation as the conductor heads away from your eye.
01:27 Adhering to this guideline does tend to simplify the final construction and minimises the number of conductors in the inner layers which will need to change twist direction at a transition point.
01:38 The situation where you may need to vary from this is with a pair of twisted pair cables.
01:44 They should always be twisted in the opposite direction to their individual twist to avoid them forming a quad, which is where all four conductors now twist around one another and each individual twisted pair is lost.
01:56 I'll show an example of this now as it is a little bit hard to explain.
02:01 I've got a pair of twisted shielded pair cables here and these are twisted with a left hand lay.
02:08 That means that each conductor passes from right to left as it heads over the top of the cable.
02:14 If I then twist these together, with a left hand lay, it's very easy to have a tidy final construction but it's also quite easy to accidentally form a quad by twisting them tightly.
02:27 Which is what I am purposefully doing here now.
02:31 So having a look at that section we can see that each individual twisted pair has been lost as now all four cables have formed a twisted quad.
02:41 This is what we want to avoid and we do this by twisting them in the opposite direction.
02:46 So if I twist these with a right hand lay, it's impossible for them to form a quad no matter how tightly they get twisted and we can still form a nice tidy bundle with that lay in the other direction.
03:00 Building the core of the harness is the most complicated part as you have no existing structure on which to build.
03:07 From our prepared wires and our design documentation we can select the cables that will make up our core, which in this instance are our four twisted shielded pair cables.
03:17 When you get to this stage, the first thing you want to do is make sure that you have nice clean hands.
03:22 You're going to be handling every part of the harness and it will pick up any dirt that's on your hands and we want to avoid any contamination getting into that harness.
03:31 With our four twisted shielded pair cables here, the first thing I'm going to do is bundle up one end with a cable tie in as tight a pattern as they can possibly be.
03:42 So that's going to be with the cables essentially forming a square, so two on the top and two on the bottom.
03:48 So I'll get a cable tie and we'll get that into position.
03:57 So you can see I've bundled those together with our cable tie in as tight a pattern as they could possibly make.
04:03 We're going to continue that pattern down the length of this harness section however the wires are going to twist around one another.
04:09 We're going to begin that twist simply by hand and we're going to do this just by feeling for a nice natural lay length that the cables want to take.
04:18 This is likely to be longer than the lay length of the subsequent layers, but that is absolutely fine.
04:24 The main aim here is to just make sure that the core is twisted together nice and tidily and is forming as circular a cross section as possible.
04:34 So twisting this together by hand really is quite easy.
04:37 You need to ensure that none of these wires are crossing over one another as they form that nice natural twist.
04:44 And once I've got a section around about 100 millimetres long, we're just going to secure that in place with another cable tie.
04:54 For our example harness section here, it is quite short so we can start from one end and work towards the other end.
05:00 If you were dealing with a complete harness and a particularly long cable section, sometimes it can be advantageous to actually start in the middle and work outwards towards either end.
05:10 This will become clear as you'll find the longer the sections of wire that you're working with, the more likely they are to tangle up.
05:18 So by starting in the middle of the harness and working outwards, you shorten the length of each section that you're actually working with and it can make things quite a lot easier.
05:26 Now that I have my lay length established, I can mount this end of our harness section into our bench vice here and this is where the build process does actually get a wee bit easier as once we've got this harness section into our bench vice, we don't need to be holding that in our hand anymore and that frees us up to more easily twist the rest of this harness section.
05:47 So we'll get this in place in our bench vice here.
05:50 You'll notice that I am protecting the harness section there with some rags, just to stop it damaging the end of those cables.
06:03 Now I've got that securely mounted in our bench vice, we can just continue twisting this along its length by hand and around about every 200 millimetres, I'm going to pop a cable tie onto it just to keep it in place and make sure we don't lose any of the work that we've done.
06:19 Really important when we're doing this that we're watching for any of these individual wires to cross over one another as that's what we're trying to avoid.
06:27 That will leave a pretty noticeable bump in the harness.
06:30 So I'm just gonna go ahead and get the rest of this harness section twisted up and secured.
06:56 Now that the entire harness core is twisted together and has a nice even lay length, we're going to mount it between our two vices.
07:04 So I'm just going to protect this end with some rags as well and we're going to clamp down on that there.
07:12 And the vices I have here have a wee handle on the bottom that if you release, you can actually move this head around, that allows me to release it and get my harness section under a bit of tension there which is what we're looking for for the next step which is going to be lacing the core.
07:29 Lacing the core refers to using some specific lacing cord to wrap around the core to keep it nice and tightly bundled.
07:38 You can lace every single layer when you're building a harness.
07:41 I typically find that's a little bit of overkill however and I usually only lace the core and the final layer of the harness.
07:49 Lacing cord is available in various different materials.
07:52 The lacing cord that I have here is a 25 pound nylon and it is wax coated.
07:57 It's also flat which means it's going to lay nice and flat onto our harness section as we wrap it around.
08:04 So I'm going to cut a length of our lacing cord here.
08:07 I mentioned earlier on that you want to have clean hands when you're undertaking this process and particularly with lacing cord that's very important as it does pick up dirt really really easily and just makes everything look a little bit nasty.
08:19 So I'm simply going to spool off a good length of this that's quite a bit longer than our harness section as I'm going to wrap it around the end multiple times in a short space and then secure it in place with some Kapton tape.
08:31 The direction of lay that the lacing cord is going to have will be opposite to our twist direction on our first layer here.
08:38 So as our first layer is a left hand lay, my lacing cord is going to have a right hand lay.
08:44 And that's going to be important for the first stage of the process which is going to be securing my lacing cord at this end as I want this end of the lacing cord to be coming out of that bundle in that right hand lay direction.
08:55 So I'm simply going to wrap this around multiple times in a short space here at the end of our harness section and then secure it in place with some Kapton tape.
09:15 With our lacing cord nicely secured at one end, we're going to start wrapping this around the harness in that opposite lay direction to the core.
09:24 The lay length of our lacing cord is going to be a wee bit shorter than that of our underlying core.
09:31 Once again it's just going to form a nice natural lay length as you twist it around the harness.
09:37 When we get to a cable tie here, we're simply going to snip that cable tie very carefully and remove it from our core.
09:44 I have a particular way that I like to cut these cable ties, and it might seem like a really small detail but if you were to nick one of the underlying wires at this stage, it can actually cost you an awful lot of time.
09:57 So what I like to do is just snip the very head of the cable tie as it means I don't have to get my flush cutters anywhere near the actual wires.
10:09 With our cable tie out of the way, we can continue the twisting process along our harness, keeping our lacing cord just under a small amount of tension as we're doing this and ensuring that it lays onto our harness core nice and flat.
10:23 It is quite easy for it to actually bunch up but if we can keep it nice and flat it's going to make all the subsequent layers just look that little bit nicer as well.
10:32 So I'm going to continue along this harness section snipping my cable ties as I reach them until I get to the end.
10:38 We're then going to wrap our lacing cord around the end multiple times in a short space and secure with a bit of Kapton tape there as well.
11:06 Once the core of the harness section is constructed, things typically get a little bit easier as we now have a base structure around which to work.
11:13 WIth the core laced, it will be quite robust and you'll be able to move it around and store it if need be.
11:20 But the next part of the process will be twisting our first layer onto the core and this requires our core to be spanning between our two vices under a small amount of tension.
11:29 So often it's best to continue on with the construction directly from this point.
11:33 Now as we have designed the first layer of our harness here to contain the correct number of wires that will result in a correct lay length, we can simply grab those wires and begin to lay them onto our core.
11:46 I'm going to do this in a couple of stages.
11:49 The first stage, I'm going to lay all of our wires at one end and I'm going to give them one twist.
11:56 I'm going to secure that with a cable tie.
11:58 Now that is going to let me measure the actual lay length and then transfer that measurement to sharpie marks along the rest of the core and once those sharpie marks are in place, I can then work with a fewer number of wires at a time and that does make the process quite a lot easier.
12:16 When I'm twisting a long harness section I like to twist around about eight wires at a time as it keeps everything reasonably easy to manage.
12:25 At this point, some thought should be given to the order in which the wires are going to be twisted onto the harness.
12:32 As much as possible, you want any wires that are going to exit the main trunk of the harness to be twisted next to one another as that is going to make the job quite a lot easier.
12:42 For our example harness here I have coil power wires, coil ground wires, and our ignition signal wires.
12:49 So I know they're going to want to be run in groups of three as chances are pretty good we would be branching off a harness section like this, directly to the coils and you would want those three wires next to one another.
13:00 Now this step does tend to get a little bit messy.
13:03 We'll try and keep everything as tidy as possible so you can clearly see what is going on, but it is the nature of the beast.
13:09 You'll see once we've got our initial twist at this end, we can let lots of the wires hang down off the bench and just work with a smaller number of wires at one time and that does keep the process much tidier.
13:21 So I've got to get all of my wires in place down this end of the harness.
13:25 Now as I mentioned, we are going to be doing these in groups of three.
13:29 So you'll see a pattern emerge that will be white, red, black, and that'll be repeated along the length of the harness.
13:36 So I'm gonna start by getting a single one of our signal wires which is white, single one of our power wires which are red, and a single one of our ground wires which are black.
13:49 I'm going to lay these wires onto our harness core here, making sure the ends of our wires here meet up with the end of our core section.
13:57 I'm going to give them one twist around our harness, making sure they stay flat and in order and then I'm just going to secure them in place with a cable tie.
14:11 I'm then going to get another set of those wires and get them twisted into place, and that's how we're going to continue until all of the wires in this layer are in place and forming one twist around our harness in this section.
14:33 Now I have mentioned before that cable ties are a disposible resource and this is a really good opportunity to show that.
14:40 You'll see that every time I put a new set of wires on here, I'll clip the old cable tie that was in place out of the way, as the new cable tie I've put in there is now securing all of our wires.
14:51 So I'm gonna go ahead and lay the rest of our wires here onto the core in the correct pattern and give them one twist.
15:36 Once we're at this point with all of our wires in place, we want to get them to form one nice even twist around our harness section.
15:44 Now for our example here we've got 18 wires in this layer in pairs of three.
15:51 So I know that I'm going to have six individual white wires counted along the top of the harness here and then I'm going to see that same white wire again as it's made one complete revolution around the harness.
16:03 With that bit of knowledge, I can go ahead and make sure I've got a nice complete even twist here with a full layer, so that means there's no gaps in this layer, and because we've designed our harness layer properly, we know we're going to have a nice correct lay length here which is approximately 30 degrees.
16:27 Now when I've got my single twist there, I've got my complete layer, I'm going to put a cable tie around that point to support it and then we're going to measure that lay length and transfer it onto our harness core aloing the length and we're then going to be able to work with a smaller number of wires at each time and that's going to make the process quite a lot easier.
16:52 So on the top of our harness here, I'm looking at one of my white wires, I'm going to count six along and I'm going to take a measurement between that same wire as it's made one complete revolution.
17:07 We've got a lay length there of 68.86 millimetres.
17:11 What I'm going to do now is transfer that measurement down the harness, marking on the core with a sharpie marker.
17:29 Using that measurement I can now deal with a smaller number of wires at one time but ensure that they maintain the correct lay length so that all of our wires can evenly fit into the layer.
17:41 As we're twisting 18 wires in this instance, I'd probably divide that by 3 and deal with just 6 wires at a time.
17:48 Now looking at the wire that I've taken my measurement from here, I can follow that around and find it in our bundle and then I'm going to grab the six wires that are next to it and twist them onto our harness, aiming for that white wire to line up with the mark on our harness core here.
18:12 Even though you're now dealing with a smaller number of wires at each time, they are going to have a tendency to tangle up at this end.
18:19 So after you've done a couple of rotations lining up with your mark on the core there, you want to comb out those wires, keeping them nice and paralel, as any individual wire cross overs in our twist pattern here, is actually going to ruin our layering and we need to avoid that.
18:37 As I progress along, twisting these six individual wires, when I've done around about 200 millimetres of length, I'm going to go ahead and secure that with a cable tie just to make sure that we don't lose any of our work, when we have to let go of those wires for any reason.
19:08 Now that I have those six wires in place, I'm simply going to grab the next six from our bundle here and undertake exactly the same process.
19:16 It's much like when we were lacing the core, when we reach a cable tie, I'm going to snip that cable tie out of the way and replace it with another cable tie that'll secure all the wires I'm currently working with.
19:29 By matching up with that measurement that we have marked on our core, I will have ensured that there is enough free space in between those first six wires that we've wrapped, to fit the rest of the wires.
19:38 And we're going to maintain that correct lay length along the length of the harness section.
20:15 Now that we've got all of our wires twisted into place for our first layer of our harness, I'm going to release this end from our vice and I'm just going to twist those wires up to the end of that core section and secure them in place with another cable tie.
20:31 That's going to let me snip these cable ties out of the way and actually secure it in place with some Kapton tape right over the Kapton tape that was securing our core.
20:50 There is a wee trick when you're doing this, if you can get it to work, it works really well.
20:55 However it's not a guaranteed thing.
20:57 If you snug up a cable tie so it is reasonably tight on the section but you can still move it, sometimes you can actually use that cable tie to help arrange those wires as you twist them.
21:08 So you can see as I'm moving this cable tie along, it's ensuring that my wires are attaining a nice twist there and they're not crossing over one another.
21:18 So I can tighten that cable tie in place and get everything nice and aligned there.
21:25 Gone a wee bit too far with that so we'll just move that cable tie back a wee bit.
21:34 Get that nice and tight and then I can snip my two cable ties here out of place and secure this end of our first layer with some Kapton tape.
22:01 With that end of the first layer on our harness section secured, I'm now going to do exactly the same thing on the other end and then we're going to get into the process of twisting our second layer.
22:27 The process for building up the rest of the layers is the same as we've seen here for our first layer.
22:32 By designing our layering beforehand it makes the physical construction much easier as you know every wire is going to be accounted for.
22:40 You'll notice that I have left our supporting cable ties in place.
22:44 Very important to do that at this stage even though our layer is secured at either end with our Kapton tape.
22:50 It really helps keep this bundled together.
22:52 As you reach those when you're working on the next layer, it's the same process, you're going to snip those out of the way and then replace them, securing all the wires that you're currently working with.
23:03 So I'm going to start by getting all of our wires into place doing our single twist, measuring the lay length, and transferring that onto the underlying layer.
23:12 Once again, a little bit of thought as to the ordering of your wires at this stage.
23:16 I've got six injector power wires and six injector signal wires, and then I've got quite a few sensor wires there as well.
23:24 So I am going to lay them in an order where any wires that are going to be branching out together are going to be next to one another.
23:31 I'm going to start with our injector wire pairs, so that's an injector power and an injector signal, get those in place, and then move onto the sensors.
24:45 With our concentric layer completed we can take a couple of measurements of this harness section and just confirm that it is actually meeting our design criteria.
24:53 So a quick measurement of the diameter of the harness section here and we're coming in at 11.39 millimetres.
25:01 Now the design said that this was going to be 11.28 millimetres.
25:05 Obviously what we're measuring here is not completely rigid, so there's a wee bit of tolerance in that process and that's definitely going to be within specification.
25:14 The other measurement I'm going to make is of the lay length.
25:17 So starting from my first red wire here I will measure along the harness, find that same wire and that will give us our lay length.
25:26 And we've got a measurement there of 100.34 millimetres.
25:31 So that is absolutely within the range of eight to 12 times the diameter of our harness section.
25:38 Good to make those measurements and confirm that you have actually met those design goals.
25:42 Other things we're looking for is that this is a nice tight bundle now and it's got that really good supreme flexibility that we're looking for.
25:50 Now the aim of this course module has been to show you the physical concentric twisting process.
25:55 Although we are working with a contrived example here on the bench, the process is the same when you're working with a complete harness.
26:02 It goes become more complicated and messy however as the lengths of the wires will be much longer.
26:08 The worked example sections of this course will show the process in detail being applied to a complete harness build.
26:15 But concentric twisting is a skill that it does take a little time to become familiar with.
26:20 So I would suggest building a few practice harness sections, much like we have here.

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