3D printing design guide
Choose a process for the part’s job, then design its walls, fits, supports and finishing together. Understand which dimensions need a sample, machining or a different route.
Choose the route by function, not layer height
For accessible precise geometry, begin with CNC machining. Additive becomes useful when shape, iteration, material placement or consolidation makes a real difference.
| Route | Consider it for | Design constraint to resolve |
|---|---|---|
| CNC machining | Precise interfaces and engineering stock materials | Cutter access, setup and geometry; a useful reference option for functional prototypes. |
| FDM | Filament prototypes, large forms and selected tooling | Layer load direction, toolpath, support contact and visible roads. |
| SLA / resin printing | Detailed visual models, clear candidates and resin-specific functions | Wash/cure access, supports and the properties of the actual cured resin. |
| SLS | Nylon ducts, clips and complex shells | Powder removal, thermal distortion and grade-specific properties. |
| MJF | Powder-bed polymer parts and repeat batches | Powder product, packing, dimensional qualification and final finishing. |
| DMLS / SLM | Metal channels, lightweight geometry and consolidation | Supports, heat treatment, powder removal, machining and inspection. |
| PolyJet | Multi-material, colour and functional resin prototypes | Material boundaries, support cleaning and the chosen resin’s service conditions. |
No technology is the universal winner for accuracy, cost or strength. The child guides identify the conditions behind useful manufacturer examples; the quote confirms order requirements.
A minimum wall is a printing limit, not a load rating
Evaluate thickness together with unsupported span, orientation and cleaning. The small feature in a manufacturer test is different from the wall of a working enclosure.
A wall is more than its thickness
A short feature and a tall free-standing wall can need different design allowances. Check height, span and access for cleaning.
Support the shape
Ribs, a return edge and shorter unsupported spans can improve stiffness. Leave room to remove powder or supports.
Schematic illustrations; not to scale. Confirm the design for the chosen material, process and final use.
Resolve
Can the feature form?
Check the selected machine, material and settings. A finer layer does not automatically produce a stronger thin wall.
Handle
Will it survive processing?
Supports, blasting, washing, polishing and assembly can damage a feature that printed successfully.
Use
Will it perform in service?
Check span, loads, creep, temperature and moisture. Add stiffness or change the geometry where needed, then test the actual requirement.
Orientation trades strength, appearance and access
There is no universally best up-facing surface. The best orientation for a datum can conflict with a cosmetic face, load path or cleaning route.
| Question | Design action | Why |
|---|---|---|
| Where does the load enter? | Mark forces, constraints and important flexures | Printed properties depend on process and direction; equal tensile strengths do not establish equal fatigue behaviour. |
| Where may supports touch? | Identify cosmetic and fitted surfaces | Support removal can leave marks and may require tool access or machining. |
| Can trapped material leave? | Provide an accessible path through the cavity | Uncured resin, loose powder and support material require different removal methods. |
| Is a large flat section necessary? | Review mass distribution and the final mounting condition | Ribs can change both stiffness and cooling; they are not a universal cure for warp. |
| What does the angle mean? | State whether it is measured from horizontal or vertical | An unsupported-overhang angle is meaningless without a reference plane and process context. |
Choose the fit and fastener before the hole offset
A clearance hole, a printed moving joint, a tapped pilot and an insert bore do different jobs. Do not size them with the same rule.
Design the mating pair
Clearance is the hole diameter minus the shaft diameter. Both parts contribute to the final fit.
Allow for the worst case
Minimum clearance = smallest hole − largest shaft. A nominal gap alone does not guarantee free movement.
Schematic illustrations; not to scale. Confirm the design for the chosen material, process and final use.
| Intent | Specify | Design action |
|---|---|---|
| Sliding or removable fit | Clearance after both parts’ dimensional variation | Include finish and environment in the tolerance stack; test a coupon when needed. |
| Interference fit | Retention, insertion load and material strain | Do not apply a universal negative hole allowance to brittle or layered parts. |
| Repeated screw assembly | Hardware, installation method and torque | Use the insert or fastener maker’s dimensions; allow enough surrounding material. |
| SLA insert | Thermoset-compatible installation | Use a suitable glue-in, captured or validated mechanical method; cured resin does not melt like a thermoplastic. |
| Snap or living hinge | Force, deflection, cycles and environment | Design root geometry and strain; tensile elongation does not establish cycle life. |
| Precision bore | Finished diameter, datum and surface requirement | Plan drilling, reaming or machining and its access before printing. |
Turn a fit into a measurable requirement
Layer height is resolution. Tolerance is an allowed dimensional range. Clearance is the space between parts. Treat them separately.
| Input or result | Value | Meaning |
|---|---|---|
| Nominal hole | 10.4 mm ±0.1 mm | Minimum hole is 10.3 mm. |
| Nominal pin | 10.0 mm ±0.1 mm | Maximum pin is 10.1 mm. |
| Worst-case diametral clearance | 10.3 − 10.1 = 0.2 mm | The minimum radial gap is 0.1 mm before other effects. |
This is arithmetic using assumed dimensions, not a claim that any process holds ±0.1 mm. Roughness, coatings, distortion and temperature may consume additional clearance.
- Draw the required finished geometry. Identify critical datums and dimensions. Agree any process compensation with the manufacturer so offsets are not applied twice.
- Inspect in the state that matters. A flexible shell measured under clamping can differ after release. Specify whether dimensions apply free-standing, assembled, dry or conditioned.
Finishing is part of the design
Define the customer-visible result and the functional interfaces. Every finish need not be applied to every face.
| Route | Can help with | Check |
|---|---|---|
| Blasting / tumbling | Cleaning and a more uniform texture | Fragile details, edges and access; the media and procedure matter. |
| Dyeing | Colour on compatible printed polymers | Base colour, colour match and penetration; do not assume through-colour in thick sections. |
| Vapor smoothing | Surface texture on compatible polymers | Final fits, fine details and any sealing requirement; verify leakage separately. |
| Paint / coating | Appearance and application-specific protection | Added coating thickness, masking and adhesion. |
| Polishing clear resin | Accessible transparent surfaces | Optical requirement and tool access; internal channels may not polish like an outer face. |
| Machining printed metal | Datums, bores and precision interfaces | Stock, workholding, cutter access and heat-treatment sequence. |
Send the requirement behind the geometry
- Model and units. Send the supported CAD or mesh format with clear units and one identifiable part per file. Keep material regions identifiable in a multi-material model.
- Function and environment. Describe load, movement, temperature, fluids, sunlight and expected life. Name the material product if one is required.
- Interfaces and appearance. Mark critical dimensions, visible faces, colour reference and the final finish. State whether a first article needs approval.
- Quantity and delivery. Include the initial batch and likely repeat quantities. Compare printing with machining or molding where those routes can meet the same requirements.
3D printing design — FAQ
What is the minimum wall thickness for 3D printing?
There is no one value across processes. Use the selected material and machine guidance, then increase or redesign for span, processing and service loads. Printable feature minima are not structural wall ratings.
Which 3D printing technology should I choose?
Start from function: filament for suitable forms and tooling, resin for detail or resin-specific performance, SLS/MJF for powder-bed polymers, metal powder bed fusion for geometry that benefits from additive, and PolyJet for compatible multi-material designs. Compare CNC for accessible precise geometry.
Does layer height equal part tolerance?
No. Layer height is a build increment. Dimensional accuracy also depends on machine, material, geometry, orientation and post-processing. Confirm the finished tolerance separately.
Do powder-bed parts need supports?
Polymer SLS and MJF generally do not need attached supports. Metal laser powder bed fusion often does, for anchoring and heat transfer as well as overhangs. All need suitable access for trapped-material removal.
Can I heat-set an insert into an SLA part?
Do not use the same melting procedure as in a thermoplastic. Cured SLA resin is a thermoset; use an appropriate glue-in, captured or validated mechanical joint.
Are printed parts isotropic or equivalent to molded parts?
Not by default. Compare printed data for the exact grade and direction, including impact, elongation and fatigue where relevant. Similar tensile strength does not establish identical behaviour in every property.
Does dyeing colour the entire printed wall?
Dye penetrates near the surface; it is not guaranteed through-colour in a thick cross-section. Powder, substrate colour and finishing process determine the result.
Design for the finished part.
Upload the model with its function, material, quantity and critical features. Confirm the process, finishing and delivery requirements in the quote.