Inside the Build: The Thursday-Night Coil
Featuring Mike Cook, Program Manager; Dan Hansen, New Product Development Engineer; Aaron Harpster, Product Development Engineer.
“It was, I believe, a Thursday night. They contacted our VP of development at eight o’clock on a Thursday.”
Welcome to Inside the Build, a podcast series that dives deep into how Forj Medical solves complex manufacturing challenges, told by the people whose knowledge, expertise, and ingenuity make Forj Medical the partner medtech companies trust when the technology is complex and the stakes are high.
The call
An OEM was deep into design verification on a new device. The EM sensor they had sourced from a different coil supplier was underperforming in their tracking system. They had a few of an older Forj-made coil in stock, sourced from a previous program, and used them as a placeholder during testing. The older coil worked. The system tracked correctly. The problem was that the older coil didn’t look the part. It had been wound on legacy equipment from the 1990s, where the wire guide ran off a stepper motor and a cam with too little resolution to lay 58-gauge wire cleanly. The coils were consistent, but consistently messy. Kite string is the description that came up more than once.
Functionally, none of that mattered. The coil was internal to the assembly and would never be seen in the finished device. But the OEM didn’t want a sub-component in their next-generation device that looked like a rat’s nest under inspection. Visual quality builds confidence, even on a part no surgeon will ever see, and the customer was clear that this needed to look like the product it was.
They called Forj’s VP of development on a Thursday evening.
The coincidence that made the timeline possible
By the time the call came in, the team had already been running experiments on the newer generation of winders. The older machines had been replaced, and the new equipment had the resolution to lay 58-gauge wire in a clean, tight wind. The coil development engineer was out on a motorcycle trip, so the request came to the manufacturing engineer who had been running tooling DOEs on the new winders.
As a stress test for a new tooling approach, the engineer had already wound this exact coil. Same wire, same core, same geometry, just to prove out a tooling concept built from a QB pin with EDM-cut features. Nine prototype coils were sitting in a tray at the engineer’s desk when the customer call came in.
There was an initial confusion. The customer used one internal name for the part, Forj used another. Once the names lined up, the answer was unusual for a Thursday-night call: the coils already existed.
What still had to be developed
The coil itself was solved. The packaging around it wasn’t. The previous generation used a heat-shrink wrap around the coil and the twisted-pair lead, which produced a soft, somewhat inconsistent shape. The new version moved to a polyimide tube with a defined inner and outer diameter. The coil sits inside the tube, gets filled with adhesive, and produces a rigid, cylindrical assembly with a clean outer surface. Easier to handle. Easier to insert into the barrel of the customer’s device. More durable through their downstream integration.
The winding process gained a second improvement at the same time. The wire being used was capable of thermal bonding, but that hadn’t been part of the prior process. The team added a hot-air stage on the winder so the coil exits the machine already bonded, replacing the older solvent-bond step. That removed an IPA wipe from the operator’s job, which had been a quiet source of damage. Operators occasionally pushed wires out of position while wiping. Removing the step removed the scrap risk.
How the iteration loop ran
The customer arrived without a finalized spec. They knew the functional requirements but hadn’t settled on the exact configuration. The team built a small matrix of prototype variants, sent them to the customer in rapid rounds, and converged through quick yes-no testing on the customer’s side. The work moved faster than the documentation could keep up with, which is normal when an OEM is closing in on DV and needs to lock a sub-component before the broader validation timeline slips. The relationship the team built through that loop has carried forward.
The follow-on programs
That original coil is now in production. A second-generation variant, slightly shorter and built around the same core architecture, is in the late stages of development. The customer plans to ramp the second version while ramping down the first, both running through the production line simultaneously. From the manufacturing side, that means designing the line for two coexisting product configurations from the start, which reduces changeover time and stabilizes throughput while the transition is happening.
A third variant is now in early proof-of-concept work.
Why the vertical integration showed up here
The lead-time advantage on this category of work comes from owning the core cutting in- house. Cut cores from outside suppliers can take months. When a customer asks for a length variant, the team can prototype within days. Combined with in-house winding, assembly, and the ability to run line transfers between Minnesota and Costa Rica based on customer preference, the same fundamental capability supports both prototyping speed at the front of a program and cost optimization once a program matures.
None of that was the deciding factor on the Thursday night call. The deciding factor was that the coil already existed. But the reason it already existed, the reason a manufacturing engineer was running tooling DOEs on production equipment in advance of any customer ask, is the same reason the follow-on programs landed here.
This has been Inside the Build, a podcast series by Forj Medical, where we’re shaping the future of life-saving devices, one build at a time. Thank you for listening. For more information, visit us at forjmedical.com.