There’s a category of work in medical device development that often goes unnoticed. It’s not the headline technology, industrial design, or regulatory strategy, but the infrastructure that makes everything else work.
Test fixtures, assembly fixtures, manufacturing jigs: call them what you want, they’re the tools that take a process from two engineers figuring it out on a bench to medical device testing that’s consistent, repeatable, and validated for production. The teams that think about test fixtures early are the ones who avoid expensive surprises later.
What Test Fixtures Actually Are
A test fixture is any purpose-built tool that helps you assemble, test, or validate a device more consistently, more efficiently, or more safely than doing it by hand. In the mechanical world that can mean something as simple as an alignment jig that takes an hour to make, or as sophisticated as an automated cyclic fatigue system running thousands of repetitions unattended overnight.
On the firmware side, the equivalent to a jig is software: it connects to the device under test, drives it through a scenario, and records what happened over a serial link, a Bluetooth connection, a debug probe, or a power analyzer measuring current while the device sleeps. We build these as hardware-in-the-loop test stations, where a real device wired to real instruments is exercised automatically on every code change. At Blur we use AI models, working directly in our codebase, to build these software fixtures, run them against real hardware, and read back the results. What it’s particularly good at is reading a few thousand lines of log to find the one line that disagrees. A person can plug in a cable and read a console, but not ten thousand times identically, and not at 2 a.m. when the build finishes.
The through-line is the same for mechanical and firmware fixtures: you’re removing variability, reducing human error, and building confidence that what you’re testing or building is doing exactly what you think it is every time.
When Do You Need a Test Fixture?
Our rule of thumb: Whenever you observe that a process could be done better, consider designing a fixture.
If an assembly step is labor-intensive, error-prone, or requires a technician to hold three things simultaneously while doing a fourth, that’s a fixture opportunity. If a test requires someone to repeat the same motion thousands of times, that’s practically a fixture requirement. Paying someone hourly to plug and unplug a cable is tedious, introduces variability into your test data, and stops being cost-effective very quickly.
The math is straightforward: weigh the investment of building the fixture against the cost of not having it. For a simple holding jig, that investment might be a day of engineering time. For an automated system with linear actuators and programmed cycles, it’s more; when the alternative is weeks of manual testing with inconsistent results, the math usually works out clearly in favor of the fixture.
The Fixture Development Process
Good fixture development starts with observation. Before sketching anything or opening a CAD program, watch the process you’re trying to improve. Understand what’s actually happening, where the sticking points are, and what a better outcome looks like. Firsthand understanding is what separates a fixture that solves the real problem from one that solves the problem you imagined.
From there, the approach broadly mirrors good product development: sketch it, model it simply, prototype it fast. A laser-cut plastic mock-up or a rough 3D print is often enough to verify the concept and get it into the hands of the people who will actually use it. Their feedback shapes the next iteration, and from there you refine toward something more robust and permanent.
The Case for Starting Early
Fixtures are often treated as a last-minute addition, something you scramble to build when you’re already in design verification and realize you need to cycle a component 5,000 times by next Friday.
We won’t lie, that approach can work. A capable team can always put something together under pressure, but the results are rarely as clean, validated, or reliable as they would be with more development time. Early fixture development means more time for iteration, better-validated systems, and fewer compromises in your test data.
The same principle applies on the manufacturing side. Assembly fixtures often get identified mid-production when volumes increase. Suddenly, what worked for five units is a bottleneck at fifty. Catching manufacturing scaling needs earlier, even conceptually, gives your engineering team time to build something that makes the production process genuinely efficient rather than just workable. Start developing fixtures early, your manufacturing team will thank you.
Good Fixture Development Captures Good Data
Beyond the efficiency gains, there’s a deeper value to well-designed test fixtures: they make your data trustworthy. When a linear actuator cycles a connector 10,000 times with consistent force and geometry, you know what you tested. When a person does it by hand for ten hours, there’s variability.
In a regulatory context, that distinction matters. The FDA wants to see that your device is safe and effective under real-world conditions. A validated, automated test fixture is a much stronger foundation for that argument than manual testing with uncontrolled variability.
The Bottom Line
Test and assembly fixtures aren’t glamorous. They’re not what gets showcased in a pitch deck or celebrated at a product launch. But they’re often what determines whether a device can actually be built and validated at scale: consistently, efficiently, and with the rigor that regulators and patients deserve.
Think about test fixtures early. Invest in them appropriately, and treat them as the engineering assets they are.
Learn more about Blur’s approach to verification and validation testing using software and hardware test fixtures.