When parts have to fit together, accuracy matters just as much as strength, because a strong part that does not seat correctly is still a failed part. SLS is an accurate process that holds consistent tolerances across an entire build, but like every manufacturing technology it has real limits that are worth understanding before you design tight fitting features and assume they will mate perfectly straight off the machine.
Knowing the realistic accuracy of the process up front helps you design clearances that work the first time, rather than chasing reprints to chase a fit. Our Perth team builds these allowances into every MJF & SLS printing job as a matter of course, but understanding them yourself leads to better designs from the outset and fewer surprises at assembly.
What accuracy to expect
As a general guide, SLS holds tolerances of around plus or minus 0.3mm on smaller dimensions, with a little more variation creeping in across larger spans where small percentage errors add up. The fine powder and thin layers give the process good repeatability, so a batch of the same part comes out consistent from one piece to the next, which is exactly what you want for production rather than a one off.
Shrinkage is an inherent part of fusing and cooling powder, and the machine and material profile are tuned to compensate for it as the part cools. Larger and bulkier sections can shift slightly more than thin walled ones because they hold more heat, so it pays to plan for that on big, chunky parts and to keep wall thickness as even as the design allows.
Designing clearances that work
For press fits, snap fits and assemblies, the reliable approach is to design the clearance deliberately rather than printing to nominal dimensions and hoping the parts happen to fit. Holes tend to come out slightly tight in SLS, so adding a small allowance, or reaming critical bores after printing, gives you a dependable fit every time instead of a lottery you have to gamble on.
When you place an order, tell us which dimensions are genuinely critical to you, because we can orient the part in the build to favour those features. Orientation affects accuracy subtly, and a little planning around your key surfaces goes a long way towards a part that drops straight into its mating components. It also helps to mark a drawing with the few features that truly matter rather than tolerancing every dimension tightly, which keeps cost down and lets us focus effort where it counts.
Checking fit before production
On a part where fit is critical, the cheapest insurance is a single test print before you commit to a batch. Printing one part lets you measure the real features, check how mating components seat together and confirm any clearances behave as expected, all for a fraction of the cost of reprinting a full run that turns out slightly off.
For incoming designs that started life as a physical object, our 3D scanning and photogrammetry service can capture the original geometry accurately so the printed part matches the part it has to mate with. Pairing a good scan with a careful test print removes most of the guesswork from a tight fit.
When you need tighter still
If a particular feature demands tolerances finer than SLS can reliably hold, all is not lost. We can post machine critical surfaces after printing, or combine processes so the part is printed and then finished to spec on the features that matter. For parts where very precise tolerances are essential throughout, CNC machining may be the better route from the start.
The simplest way to be certain is to ask. Send us your drawings with a get a quote and we will confirm exactly what is achievable for your part, and suggest the best way to hit any tight features you have flagged.