Tolerances and precision in 3D printing – what you need to know

What are tolerances in 3D printing?

In manufacturing, a tolerance is the difference between a nominal dimension and the permitted outer limits of the actual dimension. A tolerance of ±0,2 mm means that a part with a nominal dimension of 10 mm is approved if it measures between 9,8 and 10,2 mm. It sounds simple – but in practice, this is governed by a wide range of factors, and ignoring them can lead to parts that do not fit together, bind, or simply fail to function.

For those working with product development, prototypes, or production parts, understanding tolerances is absolutely crucial. The same applies if you order additive manufacturing services – you need to know what to expect from each technology.

How does precision differ between various manufacturing methods?

FDM – Fused Deposition Modeling

FDM is the most common and accessible printing technology. Plastic is extruded layer by layer and solidifies. Typical tolerances for FDM are around ±0,1–0,5 mm, depending on the machine, material, and settings.

FDM is excellent for rapid prototypes and functional parts that do not require extremely tight tolerances. Layer height, nozzle diameter, and printing temperature all affect the final result. Material choice also plays a role – ABS shrinks more than PLA, which can result in lower dimensional accuracy unless the machine is calibrated for it.

SLA – Stereolithography

SLA uses a UV laser to cure liquid resin layer by layer. The technology offers significantly higher resolution and typically delivers tolerances of ±0,05–0,15 mm. This makes SLA an excellent choice for parts with complex geometries, dental models, jewelry, or visual prototypes.

The drawback is that resin parts are often more brittle and can shrink slightly during curing if the process is not carefully controlled.

SLS – Selective Laser Sintering

SLS sinters powder (usually nylon/PA12) with a laser without requiring supports. Tolerances range from ±0,1–0,3 mm, and the technology is well-suited for complex functional parts, hinges, and parts with moving components.

SLS generally provides better isotropic mechanical properties than FDM, but the surface is porous and sometimes requires post-processing if tightness or aesthetics are important.

MJF – Multi Jet Fusion

HP's MJF technology is an evolution of powder bed technology and delivers tolerances around ±0,1–0,2 mm with faster turnaround times. MJF provides more uniform material density and is common in small-batch industrial production.

Race3D offers services in SLS and MJF for those who need functional parts with reliable tolerances and short lead times.

What affects tolerances – and what can you do about it?

1. Thermal shrinkage

Materials shrink as they cool. FDM materials like ABS and nylon shrink significantly more than PLA. If your CAD dimension is exactly 50 mm but the material shrinks by 1–2 %, it may end up at 49,0–49,5 mm. The solution is either to scale up the model compensatorily or to choose a material with lower shrinkage.

2. Layer height and resolution

A lower layer height provides better resolution in the Z-axis, but does not significantly affect the X/Y tolerance for FDM. On the other hand, an excessively high layer height can cause curved surfaces to have visible steps that also affect functional dimensions.

3. Build plate orientation

How the part is oriented during manufacturing has a major effect. A drilled hole manufactured vertically (with the axis along Z) tends to be more circular and accurate than one manufactured horizontally (with the axis along X/Y). Consider the orientation already in the design phase if precision is critical.

4. Supports and their impact

Support material is often required for overhang geometries. However, supports leave marks on the surface – and that surface may have lower dimensional accuracy. If a critical dimension is located on a surface with supports, consider redesigning the part to avoid it.

5. Machine calibration and maintenance

Even a good machine will yield poor tolerances if it is not calibrated. Worn guide rails, improperly adjusted drive belts, or incorrectly set e-steps can all result in parts that do not match the CAD file.

Design tips for better tolerances – DfAM in practice

Design for Additive Manufacturing (DfAM) is about adapting the design to the conditions of the technology rather than fighting against them. A few core principles:

• Apply tolerances correctly: Design fits with 0,2–0,4 mm clearance for FDM, and 0,1–0,2 mm for SLA/SLS depending on the assembly type.
• Avoid horizontal holes under 5 mm without supports – they tend to become oval.
• Test with prototypes: Manufacture a test plate with known dimensions to calibrate your specific system and material.
• Plan for post-processing: If you know a hole needs an exact dimension, design it 0,2 mm too small and then ream it up to the correct diameter.

Industrial requirements – when tolerances truly matter

In prototyping contexts, ±0,3 mm is often acceptable. However, in industrial applications – such as the automotive industry, medical technology, or aerospace – requirements can be much stricter. In these cases, SLA, SLS, or MJF are often chosen, combined with careful post-processing and quality control using measuring equipment such as a CMM (Coordinate Measuring Machine).

If you are unsure which technology suits your needs and what tolerances you can expect, you are welcome to contact us at Race3D for free consultation.

Summary

Tolerances in 3D printing are not a fixed number – they depend on technology, material, machine calibration, design, and orientation. In general:

• FDM: ±0,2–0,5 mm
• SLA: ±0,05–0,15 mm
• SLS: ±0,1–0,3 mm
• MJF: ±0,1–0,2 mm

By understanding these factors and designing with them in mind, you can produce parts that actually fit and function – whether it is a rapid prototype or a production-ready component.