Once you’ve studied form, surface, interface, mechanisms, structure, and internals, the final step is to rewind the process and do it again with a difference lens. Imagine the product not as an object in your hand, but as a sequence on a factory line. Assembly order, fastening methods, and testing points tell you as much about design decisions as aesthetics or components we looked at earlier.
This part of the series covers assembly sequence, design for assembly, and factory testing logic.
1. Assembly sequence
In Dyson vacuums, cyclone → filters → shell → motor → electronics. The sequence reduces dust contamination during build.
IKEA Billy bookcase is build in the rough order of fasteners first, panels second, shelves last. This sequence is chosen so one person can build it without clamps.
In smartphones, battery often goes in last to allow in-line testing of PCB and screen before final closure.
2. Design for assembly (DFA)
Snap fits vs screws: snap fits save time but are harder to service. Screws cost more labor but improve serviceability.
Modular sub-assemblies: Native new M-series purifiers use modular panels for easier mould making and service.
Fewer parts = faster line speed. Premium products often reduce part count to improve both assembly and simplicity of build.
3. Testing and QA Logic
Timex watch case screw location was changed to align with QA tooling, saving 30 seconds per unit.
In iPhone assembly, components are tested in stages before final seal to avoid scrapping entire devices.
In Native RO purifiers, water circuit is pressure-tested before casing is closed, reducing service costs.
4. Failures
Too many screws = longer assembly, higher cost.
Too many snap fits = fragile repairs.
Adhesives = cost cuts but zero serviceability.
Over-designed sub-assemblies = slower throughput, higher price.
Things to do
Pick one product and disassemble it carefully in reverse order. Write down the exact sequence of parts.
Guess why the assembly was designed that way: line speed, cost, testing.
Count the number of screws vs snap fits.
Identify where adhesives are used instead of mechanical fasteners.
Sketch an exploded view in the order it was assembled.
Ask yourself, “If I had to build 10,000 of these, what order makes the most sense?”
Compare with a premium version of the same product. Note how assembly order or fastening differs.
Count the number of parts in your teardown. Then ask: how many could be merged into one?
Log everything in your teardown journal with photos, sequence notes, and redesign ideas.
How would I simplify this assembly without sacrificing durability, serviceability, cost efficiency, speed, or user experience?