3d printing design rules
3D Printing Design Rules
3D printing is not a single process, so there is no single set of design rules. SLS and MJF build in a powder bed and need no support; FDM extrudes a bead and does; SLA cures resin in a vat and holds the finest detail. Each one has its own wall, overhang and tolerance limits, and designing for the wrong one is the most common reason a printed part disappoints.
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- Min wall (SLS/MJF)
- 0.8–1.0 mm
- Min wall (FDM)
- 1.2 mm (3 perimeters)
- Overhang limit
- 45° from vertical without support
- Tolerance
- ±0.3 mm ±0.3% typical
Printing is a design tool that can also make parts. The rules below are what keeps the design inside the process, so the first print is the one you evaluate rather than the one you reject.
Specifications
| Processes | SLS, MJF, FDM, SLA |
|---|---|
| Min wall | SLS/MJF 0.8–1.0 mm · FDM 1.2 mm · SLA 0.5 mm |
| Overhang without support | 45° from vertical (FDM) · unlimited (SLS/MJF) |
| Tolerance | ±0.3 mm ± 0.3% typical |
| Min hole | 1 mm (powder) · 0.5 mm (SLA), drilled after if critical |
| Clearance for mating parts | 0.3–0.5 mm per side |
Frequently asked questions
What is the minimum wall thickness for 3D printing?
About 0.8–1.0 mm on SLS and MJF, 1.2 mm on FDM (three perimeters at a 0.4 mm nozzle), and 0.5 mm on SLA. Thinner than the process minimum, the wall is either porous or a single unsupported bead.
Do 3D prints need support?
SLS and MJF do not — the powder bed supports the part, so any overhang and internal channel is fine. FDM needs support for anything sloping more than 45° from vertical, and SLA needs support on downward-facing surfaces.
Why are printed holes always too small?
Because the process leaves material inside the hole: powder that partially fuses, or a bead that spreads. Model holes 0.2–0.3 mm oversize, or print a pilot and drill to size where the fit matters.
Can 3D printed parts hold threads?
A printed thread will take a light load and strip under torque. For anything that will be assembled more than once, use a metal thread insert — heat-set into FDM or moulded into SLS — or design a through-bolt with a nut.
How tight a tolerance can 3D printing hold?
Around ±0.3 mm plus 0.3% of the dimension, varying with orientation. That is ten to thirty times looser than CNC machining, which is why a printed prototype often needs a machined counterpart for the critical fit.
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