Technical · SLS Design Guide · UK

SLS Design Guide

Every dimension you need before you send us the CAD. Minimum walls, pins, holes, drain holes and clearances for selective laser sintering, plus the orientation and packing rules that decide whether a part comes out of the bed straight. Numbers first, explanations after — and a free design review with every quote if you would rather just ask.

Get an instant quote → Material datasheets

SLS design guide · SLS wall thickness · minimum hole size 3D printing · design for additive manufacturing · 024 7736 0144

0.6 mm

Minimum vertical wall

1.0 mm

Minimum hole diameter

3.5 mm

Minimum drain hole

No supports

Powder bed does the work

Overview

Why SLS design rules are different

SLS fuses loose powder rather than building on supports, and that single fact drives most of the guidance below. There is no support structure to remove, so overhangs and undercuts are free and geometry moulding could never release is entirely normal. What replaces the support problem is a powder problem: every internal cavity fills with unsintered powder that has to get back out, and every part sits in a hot bed where thermal behaviour decides whether it stays flat.

So the two questions worth asking about an SLS part are: can the powder escape, and will it warp. Drain holes, clearances and lattice gaps answer the first. Wall thickness, aspect ratio and orientation answer the second.

These figures are a baseline developed around unfilled PA12 and apply to most parts in most grades. Filled and elastomeric grades deviate — those differences are set out further down. If your part sits near any of these limits, send it through the instant quote and we will review it free before anything is printed.

Reviewed by the RYSE 3D engineering team · August 2026.

Reference dimensions

SLS minimum feature sizes

The numbers, in one table. Everything below explains why they are what they are.

Feature	Minimum	Why
Unsupported wall — vertical	0.6 mm	Connected on fewer than two sides. Thinner walls may warp or detach during the build, and lose strength.
Unsupported wall — horizontal	0.3 mm	As above, in the horizontal plane.
Supported wall — vertical	0.6 mm	Connected on two or more sides. Same limit — support from neighbouring walls does not buy you a thinner section in SLS.
Supported wall — horizontal	0.3 mm	As above, in the horizontal plane.
Pin or wire diameter	0.8 mm	A feature at least twice as long as it is wide. Below 0.8 mm it may deform or break in the build or during depowdering.
Hole diameter	1.0 mm	Smaller holes may close during printing in X, Y or Z. Accuracy also falls as the wall the hole passes through gets thicker.
Drain hole diameter	3.5 mm	Enclosed cavities stay full of unsintered powder without them. Use at least two per cavity.
Assembly clearance — under 20 mm²	0.2 mm	Gap between separately printed parts intended to mesh or interface after printing.
Assembly clearance — over 20 mm²	0.4 mm	Larger interfacing faces need proportionally more clearance.
Integrated assembly — under 20 mm²	0.3 mm	Parts printed together in one build must not fuse. More clearance than a separately printed fit.
Integrated assembly — over 20 mm²	0.6 mm	As above, for larger interfacing areas.
Separate part spacing	1.0 mm min 5.0 mm recommended	Parts not meant to interact should sit at least 5 mm apart to avoid thermal warping from a neighbouring part.
Lattice gap	8.0 mm	Powder has to be cleared out of the lattice. Leave open faces so powder is not trapped inside.

Tolerances are separate from feature sizes. Our standard dimensional tolerance is ±0.3 mm for parts up to 100 mm, then ±0.3 mm for the first 100 mm plus a further ±0.1% for every 100 mm thereafter. Tighter fits, bores and sealing faces are achieved by printing near-net and machining the critical features.

Text & detail

Embossed and engraved features

Raised and recessed detail behaves differently on horizontal and vertical faces. Use a bold font wherever text has to survive the process.

Feature	Horizontal faces	Vertical faces
Embossed depth	0.15 mm	0.35 mm
Embossed width	0.35 mm	0.4 mm
Embossed text height	4.5 mm	4.5 mm
Engraved depth	0.1 mm	0.15 mm
Engraved width	0.3 mm	0.35 mm
Engraved text height	3.0 mm	3.0 mm
Text font depth	0.3 mm	0.3 mm

Engraved text can go finer than embossed — 3.0 mm against 4.5 mm minimum height — so if part marking is tight on space, recess it rather than raise it. Anything below these figures may simply not be legible on the finished part.

Designing for the process

Six things that decide whether an SLS part succeeds

Meeting the minimums gets a part printed. These get it printed well.

Keep wall thickness uniform

Sharp changes in section cool at different rates and pull the part out of shape. Where a thick base meets a thin web, transition gradually rather than abruptly. Coring out heavy sections is usually better than leaving them solid.

Reduce stress concentrations

Thin extrusions from thick bases build up stress at the junction. Fillet and blend the transitions — it costs nothing in an additive process and removes the most common crack initiation point.

Watch the aspect ratio

Long, thin, flat parts are the most warp-prone geometry in SLS. Ribs or a slight draft on extruded sections mitigate it, and orientation does the rest — see below.

Design lattices to depowder

No gap smaller than 8 mm, and leave open faces so powder has a route out. A lattice that traps powder is heavier than the drawing says and never fully cleans.

Integrate hardware deliberately

Dowel pins for precise locating features, heat-set inserts for durable threaded connections, bushings for concentric interfaces to shafts or rails. We fit threaded inserts and bonded fixings in-house, so design the boss and we will do the rest.

When in doubt, test it

Isolate the risky feature and print it on its own, in the orientation the full part will use. Print several at once, stepping the dimension up in 0.1 mm increments, and you will find the real limit for your geometry rather than the general one.

Orientation & packing

How the part sits in the bed

We control this, but it is worth knowing what we are trading off — and worth telling us which face matters most on your part.

●

Holes and pins are most accurate in Z

Circular features are most accurate with their axes vertical. Circles with an axis in the XY plane tend to elongate slightly into an ellipse — if a bore has to be round, tell us and we will stand it up.

●

Surface finish depends on which way a face points

Rounded and contoured surfaces come out smoothest facing downward. Features needing a sharp, crisp edge come out best facing up. You rarely get both on one part, so tell us which face the customer sees.

●

Wide flat parts go in at about 20°

High-aspect-ratio parts that are wide and relatively flat are printed at a slight angle, roughly 20°, to minimise warping rather than laid flat in the bed.

●

Parts sit at least 5 mm apart

Spacing keeps thermal buildup between neighbours under control and makes depowdering cleaner. Parts are distributed across the chamber rather than clustered.

●

Mating parts share a rotation

Components designed to interface are oriented in the same rotation in the bed, so their mating features carry the same directional behaviour and fit cleanly together.

●

Packing density is free capacity

There is no support structure, so the full build volume can be filled in all three axes. That is why SLS unit cost falls as quantity rises — you are paying for bed space, and a full bed is a cheap bed.

By material

Grade-specific design considerations

The figures above are a PA12 baseline. Here is where each of our five SLS grades deviates from it.

Grade	Build envelope	Design considerations
PA12	165 × 165 × 300 mm	The baseline. Balanced properties, easy to print and easy to finish — the figures in the tables above were developed around it, so no additional allowances are needed.
PA11	165 × 165 × 300 mm	More ductile and impact-tough than PA12, but more prone to warping on large cross sections in the XY plane — follow the high-aspect-ratio guidance. Integrated assemblies need at least 1 mm clearance rather than the PA12 figures. Fine features resolve slightly larger than PA12, so test before committing a batch.
PA12-GF	165 × 165 × 300 mm	Stiff and thermally stable, but the glass filler makes parts more brittle — particularly across layers. Thicken fine positive features so they survive depowdering, and orient load-bearing features into the XY plane. Surface finish is rougher than PA12, so allow a secondary finishing step where appearance matters. Escape holes should be larger, with line-of-sight access to every surface.
PA12-CF	490 × 490 × 740 mm	Runs large-format on a separate machine, so the envelope is far bigger than the other grades — this is the route for one-piece SLS parts above 300 mm. Carbon-filled and electrically conductive. As with any fibre-reinforced grade, properties are directional: orient features requiring maximum stiffness along the fibre direction and design against the Z figure.
TPU 90A	165 × 165 × 300 mm	Firm, rubber-like elastomer. Fine features on the upper surfaces of thick sections — above roughly 30–40 mm — may not resolve because of thermal buildup; hollow the geometry or re-orient. Minimum feature sizes are slightly larger than PA12. Warping shows most on bottom faces. Softer behaviour is achieved by replacing solid sections with lattice rather than changing grade.

Full property data for every grade, with ISO and ASTM methods cited and XY and Z published separately, is on the material datasheets page. Not sure which grade fits? Compare them on the SLS service page or ask us.

Honest limits

Where SLS is the wrong process

Design rules only help if the process was the right choice to begin with.

●

Parts over 300 mm in an unfilled grade

Standard SLS tops out at 165 × 165 × 300 mm. Above that you are choosing between PA12-CF at 490 × 490 × 740 mm, or large-format FDM at 500 × 500 × 900 mm.

●

Sealed hollow parts with no drain route

If the design genuinely cannot take two 3.5 mm drain holes, the powder never comes out. That is a case for splitting and bonding, or for a different process entirely.

●

Optically smooth or transparent parts

SLS leaves a matte, slightly grainy surface. Shot blast polishing and vibro polishing improve it considerably, but for a genuinely smooth or clear part the answer is SLA.

●

Bearing fits and sealing faces

Our standard tolerance will not hold a fit measured in hundredths. Print near-net and machine the critical features — tell us which faces matter at quote and we will plan for it.

●

Very high volumes of simple parts

SLS gets cheaper as the bed fills, but injection moulding still wins on unit cost for simple geometry at true production volume. We will say so if that is the better answer for you.

●

Load-path critical metal replacements

We are a polymer bureau. Fibre-reinforced nylon covers a great many load-bearing brackets and housings, but it does not replace steel or aluminium where the safety case demands metal.

FAQ

SLS design FAQ

What is the minimum wall thickness for SLS 3D printing?

0.6 mm for vertical walls and 0.3 mm for horizontal walls, whether the wall is supported by neighbouring walls or not. Below those figures a wall may warp or detach during the build, and thinner walls have reduced strength regardless. If a section has to be thinner than this, tell us at quote and we will advise whether orientation can rescue it or whether the design needs a rib.

What is the smallest hole you can print in SLS?

1.0 mm diameter is the recommended minimum in X, Y and Z. Smaller holes may close during printing. Accuracy also depends on how thick the wall is that the hole passes through — the thicker the section, the less accurate the hole. For precisely concentric holes, design an undersized pilot hole and let us ream it to final size.

Do SLS parts need support structures?

No. The surrounding unsintered powder supports the part as it builds, which is why SLS handles overhangs, undercuts and internal geometry that moulding could never release. What replaces the support problem is a powder problem: enclosed cavities need at least two drain holes of 3.5 mm or more so the unsintered powder can escape.

Why does my SLS part need drain holes?

Any enclosed cavity fills with unsintered powder during the build, and without a route out it stays there — adding weight, and leaving an internal surface that never fully cleans. Design at least two drain holes per cavity, each 3.5 mm or larger. More and larger holes make cleaning easier, and where an internal surface matters, design it so cleaning tools can reach it.

How much clearance do I need between moving SLS parts?

It depends on whether the parts are printed together. For separately printed parts intended to mesh, allow 0.2 mm on features under 20 mm2 and 0.4 mm above that. For an integrated assembly printed in one piece, allow more — 0.3 mm under 20 mm2 and 0.6 mm above — so the parts do not fuse during the build. PA11 needs at least 1 mm on integrated assemblies.

Does part orientation affect SLS quality?

Considerably. Holes and pins are most accurate with their axes in Z, and circular features in the XY plane tend to elongate slightly. Rounded surfaces finish smoothest facing downward while sharp edges finish best facing up. Wide flat parts are printed at roughly 20 degrees to reduce warping. We set orientation, but tell us which face or feature matters most and we will optimise for it.

Will you check my design before printing?

Yes, and it is free with every quote. Upload your CAD to the instant quote tool and our engineers review it for wall thickness, drain holes, clearances, orientation and grade suitability before anything is printed. We would rather flag a problem at quote than deliver a part that fails in service.

Ready when you are

Send the CAD. We will tell you what to change.

Free design review with every quote — wall thickness, drain holes, clearances, orientation and grade, checked by the engineers who run the machines.

Get an instant quote → Request free samples

Our own ISO 9001 facility in Shipston-on-Stour, Warwickshire. Mon–Thurs 8am–4pm, Fri 8am–2pm. Call 024 7736 0144 or email hello@ryse3d.com.