Agile Wiring Form Boards for the Aerospace Industry

December 17, 2024

Spingarage has never had a theoretical phase. We didn’t spend months raising capital, hiring developers, writing software, and designing factory layouts before building our first harnesses. Our first wiring harness contract started with a run to Home Depot the night before the parts showed up to buy every folding table they had in stock. We had long wiring runs to build, so I laid out 60’ long runs and marked every foot. The next day, as we laid out circuitous runs totalling over 400’, we were frustrated by wiring falling off the sides of the table – this prompted another run to Home Depot for a hot glue gun and every downspout clip in stock. Problem solved.

A month later, our contracts looked massively different. Our longest runs were under 50’, harnesses were far more complicated, and length tolerances and breakouts became substantially more critical. There was some semblance of production, but by and large, every harness was different from one to the next. Pulling from experience in aerospace sheet metal manufacturing, we designed cable stanchions that used clecos to clip into an 1/8” aluminium baseplate, and the 3D printer started working overtime kicking these out as fast as it could. At the time, we had a very large CNC bridge mill, which we used to drill some 12,000 holes in 2’x4’ aluminium panels overnight. I bought some lightweight folding table bases which rapidly became one of the least popular additions to the shop. We had the beginnings of our reconfigurable form board system.

We kept iterating on a weekly or sometimes daily basis, and we still do. Fundamentally, we’ve identified a few key requirements that drive this development:

• The only constant is change – the system needs to be able to be reconfigured at the drop of a hat for harnesses of different lengths, sizes, wire types, and connector families.
• Fidgeting time matters – in a poorly designed system, technicians spend a remarkable amount of time catching a roll of string tie before it rolls off the edge of the table, or messing with a cable route so that it doesn’t keep popping out of the stanchion.
• Clutter is evil – every shop is familiar with the mess that is a build table partway through a build. “A place for everything, and everything in its place” was a guiding concept of our formboard development.
• Repeatability is essential – we need to be able to build the same harness over and over and over again, and we need to capture that ability with low overhead the first time we build.
• Traceability – when a layout changes, we need to know what changed, when, why, and what serial numbers were affected.

All of these requirements need to be addressable in build quantities from a single unit into the thousands. Like everything at Spingarage, it doesn’t need to be fancy – it just needs to work.

System Elements

Years later, the system has become a powerful tool that helps us in the prototyping phase and provides a low-friction pipeline to capture prototype configurations to be carried into production, even during those hair-on-fire same-day builds. Here are some of the basic elements of our system:

• Stanchions. We have 3 different sizes of stanchion that are used and will likely produce more. The largest uses integral 3D-printed springs to retain cables, and is designed to allow wires to be very rapidly clipped in on long runs. The two smaller sizes are used for more intricate harnesses typically bound for box builds and group 1-3 UAVs, and provide rubber band clips to retain wires where needed. We’ve found it’s often not necessary to retain the wires in every stanchion, so having the option provides flexibility. Like the first iteration, these are held in place with clecos, meaning a route can be clipped into place in seconds.
• Connector mounts. We found that a key source of inaccuracy was the positioning of the connector at the end of a run – a loose fit meant that every technician would build the harness a little differently. Rather than rely on drawings and measurements, we designed connector mounts for a wide variety of our commonly used connectors that grab the connector precisely right behind the coupling ring and position it repeatably within 1/8” at the end of the run. The mount’s connector designation is 3D printed on the side of the mount to avoid mismatches.a
• String tie dispenser. This came from a personal pet peeve of mine – it didn’t seem to matter what tape tricks we used, string tie was never where I needed it, always in the way, and inevitably, on the floor. As a guideline, we place at least one string tie dispenser on each side per 4’ section of table.
• Tables. We looked at a lot of different options for how to actually support the form boards, and eventually settled on Maker Pipe. While extruded aluminum solutions like 80/20 would certainly look fancier, what mattered to us was the ability to make a build table of any size and shape at the drop of a hat, and that’s what we regularly do. We’ll quickly mock up a coffee-stir-stick model of a table, and then our technicians have everything they need to build it full scale, usually within a couple of hours. It’s affordable and practical to keep plenty of inventory of fittings and conduit on hand to build whatever we need.
  
  Most of our tables include a few common features:
  
  ‍A laptop mount: Our software is the backbone of our shop, and ensuring it’s available everywhere is essential. Foot pedals are provided for our technicians to use our pinning application hands-free.
  
  ‍At least one heat gun holster: Always having a heat gun within arm’s reach saves enormous amounts of time. We briefly experimented with a tool balancer overhead, but it was impractical.
  
  ‍A Wall Control panel: This usually holds rubber bands, thermal gloves for heat shrinking, and any other essentials to the build. For higher volume builds, we often use tilt-out boxes to hold stock such as connectors, boots, and labels.
  
  ‍A 5S tool caddy: These hold essential tools like insertion/extraction tools, high-quality side cutters, a wire spoon, and more. We ask technicians to restock them prior to lunch and end of day, so it’s easy to see if anything is missing.
• Traceability and repeatability. We needed to be able to accommodate both top-down and bottom-up layouts – sometimes our customers bring us a toleranced, dimensioned drawing of what they need, and sometimes we get a partially completed airframe and the definition is “make it fit.” Working efficiently with either approach is our bread and butter, and retaining that capability has been essential in developing our form board system. We use a layout sheet to record the type, location, and orientation of every stanchion. Without the rest of the system, this could be a pretty time-intensive task; however, with the structure we have in place, it takes about 15 minutes. These layout sheets are released documents which are scanned and saved with every first article. Even if a customer only requests one harness, we have the configuration of the build fixturing to make it efficient and easy for us to build another one at a moment’s notice.

Future Improvements

This system is one of many pieces of our ecosystem that help us build world-class wiring harnesses at a lightning-fast pace, minimize relearning, maximize company-wide knowledge retention and accessibility, and enable continuous improvement. They’re far from perfect, of course, and there’s a huge backlog of tweaks and improvements. To name a few:

• Improving the ergonomics of our computer mounts. Whenever the computer is exactly where you want it, you have to move to the other side of the table, and it’s in the way.
• Parameterizing the CAD models for our stanchions and connector mounts to allow more iteration and generation of new versions.
• Redrilling our form boards with tighter hole spacing. We occasionally add extra holes to precisely position a breakout, and I’d like to make that the norm. ½” or even tighter spacing should be feasible.
• Implementing automated generation of form board layout drawings from our layout sheets to make it seamless for customers who end up generating their own layout drawings.

Overall, we’re proud of the efficiency gains we’ve achieved and we’re going to keep pushing to make our shop floor the best in the world.