It is easy to design a single part in isolation and quietly forget that it has to join others to do its job. Design for assembly is the discipline of thinking about the whole product at once, so the pieces come together quickly, line up correctly and stay put without anyone having to force, file or fight them into place on the bench at the end of a long day.
Our CAD team models parts as assemblies wherever they interact, checking the fit on screen before anything is ever made. It is far cheaper to discover a clash or a missing clearance in the model than to find it when a box of freshly made parts simply refuses to go together. A little planning here saves a great deal of frustration and cost later on.
Make it obvious and easy
Good assembly design removes choices the assembler should never have to make. Features that only fit one way prevent parts going in backwards, and clear lead ins guide pins and bosses into place without anyone needing to align them by eye. The aim is a part that almost assembles itself, where the right way is the only easy way and mistakes become genuinely hard to make.
Reducing the sheer number of separate parts helps enormously too. Every fastener and component is another chance for error and another cost in time and inventory, so combining several features into a single moulded or printed part is often the cheapest improvement you can make to a whole product, and it usually makes the result more robust into the bargain.
Designing the joins
How parts fasten together deserves real thought rather than a default choice. Snap fits are fast and tool free but need the right material and carefully designed geometry to last. Screw bosses are reliable and easy to service. Glued or welded joints suit permanent assemblies. Each of these decisions shapes the geometry of the surrounding model in its own particular way.
Clearance is the other half of the story and just as important. Parts that have to move need genuine room to do so without binding, while parts that must locate firmly need a tighter, more controlled fit. The model has to reflect both of these realities precisely, because a clearance that is wrong by a fraction of a millimetre can ruin an otherwise sound design.
Common assembly features we add
Most well behaved assemblies rely on the same small set of features, used thoughtfully and sized to the material. None of them are complicated on their own, but choosing the right one for each join is what makes a product quick to put together and pleasant to service. We pick them deliberately rather than by habit or by whatever happens to be easiest to draw.
- Lead in chamfers that guide pins and bosses into place.
- Locating pins or keyed features so parts only fit one way.
- Snap fits sized to the material for tool free assembly.
- Screw bosses for joints that must be opened and serviced.
- Designed clearance so moving parts never bind in use.
Proving it before production
Modelling the full assembly lets us check for clashes, confirm alignment and simulate movement before committing to making any parts. We can spot two components trying to occupy the same space, or a fastener with no room for a tool, all while the design is still easy to change. That digital check catches a surprising number of issues at no cost at all.
Even so, we often print a first set through prototype development to confirm the real world fit, since plastic behaves slightly differently to a perfect digital model and tolerances stack up in ways that are hard to predict. Bring us your concept and get a quote, and we will make sure the pieces actually go together.