One of the most striking things SLS can do is print whole assemblies that already move, straight out of the machine, with no assembly step at all. Because loose powder fills every gap between components as they print, you can build hinges, gears, chains, ball joints and captive parts that work the moment the powder is cleared away. It feels a little like magic the first time you see it, and it genuinely changes how you can approach a mechanism.
This printed in place capability removes manufacturing and assembly stages that would otherwise eat time and money, and on the right project the savings are substantial. It is a genuine and often underused advantage of working with our MJF & SLS printing service, and it can dramatically reduce the part count of a finished product while making it more robust.
How parts stay separate
The whole trick comes down to clearance. As long as you leave enough of a gap between two surfaces that need to move relative to each other, the powder sitting in that gap never receives enough energy to fuse, so the two parts come out as distinct components rather than welded into one solid lump. After printing, the loose powder in the gap is blasted away and the assembly is suddenly free to move, often with a satisfying first click or rotation.
Typical clearances for moving parts start around 0.3 to 0.5mm, although the right figure depends on the size of the parts and the type of motion involved. Too little and the parts lock together, too much and the joint feels sloppy, so it is worth getting right. Larger joints generally need a touch more clearance because there is more surface for stray powder to bridge.
Where it shines
Printed in place assemblies suit mechanisms, enclosures with integrated hinges, cable carriers, articulated models and demonstration pieces that need to move convincingly. Reducing the part count also means fewer fasteners to buy, less inventory to manage and faster delivery, because there is nothing to bolt together once the part is printed and cleaned.
It is especially powerful for prototype development, where proving that a mechanism actually works in a single print can save weeks of back and forth. Instead of modelling, printing and assembling separate components, you test the whole concept in one go and learn far more from a single build. That is a real advantage when a design is still changing quickly and you want answers within a day or two rather than after a long assembly process.
Powder removal in tight gaps
The flip side of building everything in one piece is that the powder still has to come out of every joint, and a tight internal mechanism can hold powder stubbornly. Plan blasting access from the outset by keeping moving surfaces reachable, adding flush channels where you can, and avoiding deep blind pockets that the blast media cannot reach to clear.
For an intricate assembly, it is worth printing a small test version first to confirm the powder clears and the joints move as intended. A quick trial print costs little and removes the risk of committing a large, complex build that arrives partly seized with trapped powder.
Designing it right
Success with printed assemblies comes down to clearances, powder escape and a handful of sensible rules that keep the parts free and the powder removable. Get these right and the assembly works first time, get them wrong and you risk parts fused together or full of trapped powder.
- Leave generous clearance between any surfaces that must move.
- Add powder escape paths so loose powder can be flushed out.
- Avoid fully enclosed cavities that permanently trap unfused powder.
- Test fit a small version before committing to a large build.
- Keep moving parts accessible so blasting can reach the gaps.