SLS gives designers an enormous amount of creative freedom, but there is still a handful of important dimensional rules that keep parts printable, strong and free of trapped powder. Walls that are made too thin can bow during the build or break during cleaning, while features that are too fine simply may not survive the bead blasting that follows printing. Knowing the practical limits lets you design with confidence rather than guessing.
Getting these basics right from the start means fewer unwelcome surprises and consistently better parts. Our team checks all of them on every single MJF & SLS printing job before it runs, but designing with the numbers already in mind saves time, avoids reprints and gets you a better result on the first attempt.
Walls and features
As a general guide, aim for walls of at least 1mm in thickness, and ideally closer to 1.5mm for any part that has to carry load or take handling. Very thin walls can bow or distort slightly during the build as the part heats and cools, and they tend to feel fragile once the part has been cleaned, so it is worth adding a little extra thickness wherever strength genuinely matters.
Small embossed or engraved details such as text and logos should be kept a touch larger and bolder than you might instinctively expect, so that they still read clearly and crisply after the bead blasting step has gently softened the finest edges. Sharp internal corners are best replaced with small radii too, since a rounded corner spreads stress and prints more cleanly than a tight angle.
Clearances and moving parts
For any assembly that needs to move or be taken apart, leave a clearance of around 0.3 to 0.5mm between the surfaces so that the powder sitting in that gap never receives enough energy to fuse. Provide too little clearance and the parts will lock solidly together as one piece, while too much clearance leaves the fit feeling loose and sloppy in the hand.
Holes and printed threads both tend to come out very slightly tight in SLS, so it is wise to design in a small allowance from the outset, or simply plan to ream the critical bores to size after printing for a precise and repeatable fit. For threaded assemblies, printing a slightly undersized hole and tapping it afterwards, or using a threaded insert, gives a far more durable and repeatable thread than relying on fine printed threads alone.
Powder escape and hollows
Any hollow or enclosed section needs at least one escape hole, and ideally two so the powder can flow out one side as air enters the other. A practical minimum is around 4 to 5mm across for an escape hole, since a tiny pinhole clogs quickly and leaves powder rattling around inside the part, adding weight and unbalancing it.
Position the holes at the low points of the cavity in the orientation the part is cleaned, and keep internal channels as smooth and continuous as you can so there are no dead pockets where powder can hide. Where a visible hole would spoil the look, we can place it discreetly and plug it afterwards. A quick mental walk through how powder would drain from each cavity, in the orientation the part will be cleaned, catches most trapped powder problems before they happen.
Quick design checklist
Keeping a few key numbers in mind as you model makes the large majority of SLS parts print correctly the very first time, with no costly back and forth to correct features that were just outside the practical limits of the process.
- Walls of at least 1mm, and more for load bearing parts.
- Clearance of 0.3 to 0.5mm between any moving surfaces.
- Escape holes of 4 to 5mm for every hollow section.
- Slightly oversize small text and fine raised details.
- Plan to ream critical holes and bores to final size.