Need help? Call 0115 794 0445
SLA 3D printing is widely recognised for its high accuracy and resolution, making it ideal for applications where fine details and tight tolerances are critical. Whether you are producing dental models, engineering prototypes or small production components, understanding how SLA performs dimensionally is key to evaluating its suitability. This post outlines typical SLA tolerances, influencing factors, comparative technologies and real-world use cases, along with a quick-reference cheat sheet for feature planning.
Stereolithography achieves high accuracy by using a focused laser to selectively cure resin in very thin layers. Compared to extrusion or powder-based processes, the layer adhesion and detail resolution in SLA is more consistent, especially on small geometries.
Parts under 100 mm typically stay within ±0.05 mm if printed on a calibrated industrial machine with stable ambient conditions. Larger parts can introduce minor dimensional drift, mostly along the vertical axis.
Field Insight: If your part includes alignment features like pin holes or press fits, orienting those features on the XY plane provides more repeatable results.
| Feature Type | Minimum Size (Reliable) | Typical Accuracy | Notes |
|---|---|---|---|
| Wall thickness | 0.5 mm (rigid resins) | ±0.1 mm | May require increase for structural loads |
| Holes and slots | ≥0.3 mm diameter | ±0.05 to ±0.1 mm | Often prints slightly undersized |
| Bosses or pegs | ≥0.5 mm diameter | ±0.05 to ±0.1 mm | Allow 0.1 mm clearance for press fits |
| Text or engraving | ≥0.2 mm stroke width | ±0.05 mm resolution | Fine serif fonts may not resolve cleanly |
| Snap fits and enclosures | ≥0.8 mm feature thickness | ±0.1 mm | Consider post-cure shrinkage in design |
Designing for SLA requires a different mindset from traditional CNC or injection moulding workflows. Features that print well on paper may not hold dimensional integrity unless optimised for the SLA process environment
Due to resin expansion and post-cure shrinkage, mating components benefit from at least 0.1 mm clearance. For cylindrical fits or rotating shafts, increasing clearance to 0.15 mm improves repeatability across batches.
Designs with tightly nested geometries or multi-point contacts are prone to distortion. Leave small reliefs or chamfers on assembly points to absorb minor geometric deviations without forcing interference.
Ribs, fins and frames under 1 mm in thickness should be supported by a larger base or perimeter to prevent curling. Thin walls benefit from being printed perpendicular to the build platform to avoid distortion due to peel forces.
Light bleed or overcuring can affect features such as small holes, logos or detailed textures. Resins with lower viscosity help reduce this effect, but designers should assume a slight positive deviation on enclosed or internal features.
| Technology | Tolerance Range | Surface Finish | Ideal Use Cases |
|---|---|---|---|
| SLA | ±0.05 to ±0.15 mm | Smooth, glossy | Medical, precision parts, tooling — compare SLA vs FDM accuracy and finish |
| FDM | ±0.2 to ±0.5 mm | Layered, rougher | Basic prototypes, mechanical fixtures |
| SLS (Nylon) | ±0.2 mm | Slight grain texture | Functional brackets, load-bearing use |
| MJF | ±0.2 mm | Uniform grey finish | Production PA12, enclosures |
| DLP | ±0.05 mm | Comparable to SLA | Small parts, dental, miniatures |
SLA machines require careful optical alignment. The laser must stay consistently focused throughout the XY range, and the resin tank surface must be free of haze. Optical drift or tank warping can cause dimensional inconsistencies, especially over long builds.
All SLA resins shrink slightly during polymerisation. Shrinkage values range from 1.5 to 3 percent, depending on the formulation. High-performance resins with glass or ceramic fillers exhibit lower shrinkage but may be more brittle.
Field Insight: Avoid switching resin types mid-project unless re-validating all critical dimensions. Each resin formulation behaves differently, even between similar rigid families.
Peel forces can introduce layer shift or distortion, particularly on tall or asymmetric geometries. Using thicker supports and a slower peel rate minimises this effect. For parts over 150 mm tall, consider breaking the part into sections to preserve XY fidelity.
Even small changes in post-cure duration or UV intensity affect final dimensions. For production workflows, curing cycles should be timed, standardised and matched to the resin manufacturer’s guidance. Over-curing may cause thin features to warp or become brittle.
| Resin Type | Dimensional Stability | Typical Use Case | Notes |
|---|---|---|---|
| Standard resin | Moderate | Prototypes, concept models | May require finishing for assemblies |
| Rigid resin (glass) | High | Enclosures, connectors, brackets | Lower shrinkage, brittle under impact. See our full SLA resin material selection guide for mechanical properties and use cases. |
| Flexible resin | Low | Seals, gaskets, flexible clips | High expansion during cure, poor tolerance |
| Dental resin | Very high | Surgical guides, aligner models | Controlled shrinkage, verified accuracy |
| High-temp resin | Moderate | Tooling, moulds, fixtures | Slight warping in thin areas |
| Biocompatible resin | High | Medical device housings, skin contact | Tight tolerance control, certified handling |
A UK-based product designer developing a wearable medical sensor used SLA printing for the enclosure and clip mechanism. The device required tolerances within ±0.08 mm to ensure that the charging port and internal mounts aligned with a custom PCB.
By using a rigid grey resin on a Form 3B printer and orienting the enclosure horizontally, the parts measured within ±0.06 mm on all features post-curing. The customer was able to complete three assembly iterations in one week, significantly reducing lead time compared to CNC machining.
When precision matters, verifying printed tolerances through inspection is essential. In industrial workflows, SLA is often integrated with digital calliper measurement, laser scanning, or CMM (coordinate measuring machine) analysis to confirm that parts meet design intent.
For prototypes, calipers are often sufficient to check wall thickness, slot widths or mating gaps. However, for multi-part assemblies or validation parts, a structured inspection protocol is advised.
Key best practices:
Measure multiple locations on critical features to account for localised deviations
Verify both as-printed and post-cured dimensions
Use resin-specific dimensional data provided by the manufacturer
For example, Formlabs publishes dimensional accuracy specifications and validation white papers for each of its engineering resins. These documents are useful when benchmarking tolerances for fixtures, housings or mechanical assemblies.
In a production context, consistency between builds is as important as accuracy. SLA can be sensitive to environmental changes, resin age and printer calibration. Maintaining a controlled workflow improves dimensional stability across multiple print runs.
Field Insight: Keep a log of part orientation, printer settings, resin batch and post-cure timing for each job. Repeatability is best achieved when variables are held constant.
For tolerances under ±0.05 mm, CNC machining is still more reliable. However, SLA has significant advantages in time and cost when working with complex geometries or short runs.
Quick iterations during R and D
Complex internal features with smooth walls
Reducing cost per part on low volume production
A growing number of engineers are combining SLA and machining by printing near net shape components and finishing them via milling or reaming. This hybrid approach balances speed with dimensional control.
Example: An electronics firm prints SLA control housings with internal bosses, then reams key holes to achieve ±0.02 mm positional accuracy.
For engineers evaluating SLA capabilities, two additional Formlabs resources are highly recommended:
These documents explain resin selection, print orientation, and post-processing control with examples and dimensional data.
Not reliably for entire parts, but localised features such as snap fits or slots can reach this level with careful design and post-processing. Parts under 50 mm generally yield the best results.
SLA resins are sensitive to UV exposure and humidity. Before and after printing, store parts and material in a dry, temperature-controlled environment to avoid swelling or softening.
Yes, but for precision threads, it is better to print undersized and post-machine, or to design in captive nuts or thread inserts. SLA threads are best suited for light-duty fastening.
Industrial SLA systems often offer more consistent accuracy due to better environmental control, larger build volumes, and rigid optics. Desktop systems can achieve similar results with proper maintenance and calibration.
For consistent results, recalibration and resin tank inspection should be done every 15 to 20 builds, or whenever switching to a new resin or print profile.
SLA 3D printing delivers excellent dimensional accuracy across a wide range of engineering and design applications. With tolerances in the ±0.05 mm to ±0.15 mm range, it is particularly well suited for components with fine features, snap-fit geometries and tight enclosures. By understanding the material, orientation and post-processing parameters, engineers can achieve repeatable, production-grade results.
👉 Need tight tolerances in your next prototype? Get a 3D Printing Quote or explore our 3D Printing Services and Technologies Overview.
Nottingham’s universities, schools, and research centres are embracing 3D printing to transform the way students and academics learn, teach, and…
Designing for Selective Laser Sintering (SLS) requires careful attention to wall thickness, tolerances, shrinkage, and part orientation. Unlike SLA or…
Birmingham’s automotive sector is turning to automotive 3D printing Birmingham solutions to speed up prototyping, reduce production costs, and create…
CELEBRATE ENGLAND IN THE EURO SEMI-FINALS!
ENJOY 20% OFF YOUR NEXT ORDER USING CODE:
ENG-EUR
HURRY! ONLY 66 COUPONS AVAILABLE
DISCOUNT CODE REQUIRED (MAX DISCOUNT £50) PROMOTION T&C’s APPLY AND VALID UNTIL 14/07/2024
