Why Manual Assembly is Best

What we have lost in the pursuit of efficiency

I am an old-fashioned engineer. I will be retiring soon, and this will probably be my last column. I’ll be discussing the art of building wire harnesses.

The Advantages of Manually Assembled Harnesses

In my long career working with electrical devices, I’ve come to regard the binding of wires and cables as a true art. These assemblies are known as “wire harnesses.” In order to connect the electronic components inside a device, or to connect circuit boards to each other, you need wires. If only a few wires are required, the task is simple. However, most projects require dozens of wires that correctly connect components located in various positions, creating something like a net of wires. Connecting wires individually is therefore not only time-consuming, it makes maintaining quality difficult. Wire harnesses solve this problem.

Wire harnesses are assembled using a board, roughly A1 in size, covered with nails to create a route map of sorts, that shows the lengths of the wires and the positions of branches (imagine a pinball machine). First, a blueline wiring diagram is pasted onto the board, then nails are hammered into the points from which wires and cables originate, terminate, and travel through. Next, the requisite wires and cables are run via the appropriate path, following the wiring table.

Once all the wires and cables are in the positions indicated on the diagram, it’s time to start tying them together. Traditionally, groups of wires were bundled together with waxed thread until the bundle had morphed into a three-dimensional harness. Waxed thread was later replaced with kite twine due to flammability concerns, although waxed thread was much easier to work with, and resulted in a tidier harness. This is probably why engineers in the old days regarded waxed thread as the best option (I was deeply disappointed when I could no longer use it). Eventually, we were told that kite twine was flammable as well, so the industry switched to fire-resistant cable ties. With cable ties, however, there is always a bit of plastic protruding from the tie, making the harness less likely to fit snugly into the case, and it is less visually pleasing. I’d like to see a new material developed with properties similar to waxed thread.

The advantage of assembling harnesses manually is the ability to standardize their shape, thereby ensuring a more consistent quality, regardless of who connects them. By building them myself, I quickly learned that a properly constructed harnesses can eliminate parasitic oscillation and reduce noise. Earlier in my career, whenever I had to opportunity to see the workmanship of a more experienced engineers, it made me appreciate that building a harness was not just a matter of tying wires together. Rather, it was important to take the time to determine the optimum wiring configuration.

The Legacy of Harness Kits

These days, assembly tends to involve connecting circuit boards using mass-produced wire harness kits. However, if the wires in the kit are longer than they need to be, different assemblers will route them via different paths, so it is rare to find two devices wired the same way. To counter this, we sometimes tie off part of the harness before it is connected. Soldering is another task that goes hand-in-hand with harness building, although these days soldering tends to be performed using connectors, and manual soldering is avoided.

Whenever I have cause to look inside a power supply that has been in use for several decades, I always come away feeling that I would rather buy a supply that uses a manually assembled harness soldered into place. However, assemblers and service people prefer harness kits because of the efficiency they offer. In manufacturing (at least in the case of mass production), the trend to do away with manual processes may now be impossible to reverse.

In order to cheaply build devices to a certain minimum quality, manufacturers have had to become more efficient. However, this efficiency appears to have resulted in devices that are more disposable. While repairing devices is still an option, the difficulty in supplying parts means manufacturers generally only offer after-sales service for a limited time. Owners are therefore sometimes unable to have their devices repaired. Furthermore, regardless of your device’s age, you will also be unable to have it repaired if you are unlucky enough to have bought it from a defunct manufacturer. You will be forced to throw the device away. It is no longer the owner, but the manufacturer that decides the fate of electronic devices.

Our Last Defence

While opinion is divided as to whether the shift to disposable devices is a good thing, it doesn’t feel right to me. I don’t like the idea of a world where if something breaks down you have no choice but to throw it away. This is not just out of concern for the environment. It feels like a waste of a good product and somehow risky too. In the software industry, we see cases where vendors of software used to create textual documents go bankrupt, meaning that when users of the software upgrade their operating systems, the software will no longer work (and cannot be upgraded), rendering all the files on it useless. This goes to show that formats that are not dependent on their environment (such as.txt) are best.

In engineering, I believe that manual assembly is our last and most powerful defence. While we cannot help the fact that many electronic devices will eventually become disposable, I believe there is still a place for devices that are hand serviceable. In fact, I believe there needs to be. I hope that those who are starting out in engineering careers adopt a similar perspective. The engineering process does not end once a device has been assembled. Rather, I believe the real test of an engineer is how long his or her device can be used for.

The Value of Manual Assembly

Let me conclude by returning to the topic of wire harnesses. Recent years have seen a drop in demand for manually assembled harnesses, and a countless number of manufacturers have gone out of business due to ageing workforces. This is a real pity. There is currently a movement towards smarter working habits. I think we need to not only improve our productivity, but also reassess the value of the manual-manufacturing processes. Devices that have been built by hand can be repaired by hand too. At the risk of stating the obvious, I believe that in the future, manually assembled products will find a new place in the sun.

Please feel free to contact us with any questions or concerns.

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