If you work with 3D printed light-cured parts—whether for prototypes, medical models, or jewelry—understanding surface roughness is critical to meeting quality and functional needs. Light-cured 3D printing (like SLA and DLP) is known for high detail, but its surface roughness can vary widely from Ra 0.5 μm to Ra 5 μm depending on key factors. This guide breaks down typical roughness ranges, core influencing factors, practical application standards, and actionable tips to improve surface quality.
1. Typical Roughness Ranges for 3D Printed Light-Cured Surfaces
Light-cured 3D printing (SLA and DLP) produces smoother surfaces than many other technologies (e.g., FDM), but the exact roughness depends on technology type, parameters, and materials. Below is a detailed breakdown of standard ranges:
| Technology Type | Typical Roughness (Ra) | Optimal Roughness (With Optimization) | Key Advantages for Surface Quality |
| SLA (Stereolithic) | 1 μm ~ 3 μm | < 1 μm | High laser precision, minimal layer lines |
| DLP (Digital Light Processing) | 1 μm ~ 5 μm | ~ 1 μm (High-Resolution DLP) | Fast printing; 4K projectors narrow roughness gaps with SLA |
| General-Purpose Resin (Any Tech) | 2 μm ~ 5 μm | 1 μm ~ 2 μm (With Post-Processing) | Cost-effective; suitable for non-critical prototypes |
| High-Precision Resin (e.g., Dental) | < 1 μm | 0.5 μm ~ 1 μm (With Fine Tuning) | Low shrinkage; ideal for medical or jewelry parts |
Note: Ra (Average Surface Roughness) is the most common metric—lower values mean smoother surfaces. For reference, a polished metal surface has an Ra of ~0.02 μm, while a standard light-cured part (without post-processing) falls between 1 μm ~ 3 μm.
2. 4 Core Factors That Impact Light-Cured Surface Roughness
Surface roughness isn’t random—it’s shaped by controllable factors. Understanding these lets you adjust parameters to achieve your desired smoothness. Below is a breakdown with specific examples and data:
(1) Printing Technology & Equipment Precision
The type of light-curing technology and device resolution directly affect surface quality:
- SLA: Uses a focused UV laser to cure resin layer by layer. Industrial-grade SLA machines (e.g., Stratasys) have laser spot sizes as small as 0.02 mm, producing surfaces with Ra < 1 μm. Consumer-grade SLA machines may have larger spots (0.05 mm ~ 0.1 mm), leading to Ra 2 μm ~ 3 μm.
- DLP: Uses a projector to cure entire layers at once. Resolution matters here—4K DLP projectors (with smaller pixel sizes) can reach Ra ~ 1 μm, while 1080p projectors may result in Ra 3 μm ~ 5 μm due to visible pixel edges.
(2) Printing Parameters
Even with the right equipment, poor parameter settings can ruin surface smoothness. The two most critical parameters are:
Layer Thickness
Thinner layers mean fewer visible layer lines, but overly thin layers can cause resin flow issues. Here’s how layer thickness impacts roughness:
| Layer Thickness | Typical Roughness (Ra) | Notes |
| 0.025 mm | 0.5 μm ~ 1 μm | Ideal for high-detail parts (e.g., jewelry) |
| 0.05 mm | 1 μm ~ 2 μm | Balances smoothness and print speed |
| 0.1 mm | 2 μm ~ 3 μm | Fast printing; visible layer lines |
| > 0.1 mm | 3 μm ~ 5 μm | Only for rough prototypes |
Exposure Time
- Insufficient exposure: Resin doesn’t cure fully, leaving sticky, uneven surfaces (Ra can jump to 4 μm ~ 6 μm).
- Overexposure: Resin shrinks excessively, causing warping or surface cracks (Ra increases by 1 μm ~ 2 μm).
Best practice: Follow the resin manufacturer’s recommended exposure time (e.g., 5 seconds per layer for standard resin).
(3) Resin Material Properties
Not all resins are equal—formulation affects shrinkage and surface finish:
- Shrinkage: Most resins shrink 2% ~ 8% during curing. High-shrinkage resins (e.g., general-purpose resin) pull the surface unevenly, leading to Ra 2 μm ~ 5 μm. Low-shrinkage resins (e.g., dental-specific resin) shrink < 2%, producing Ra < 1 μm.
- Resin Type:
- General-purpose resin: Ra 2 μm ~ 5 μm; affordable but rough.
- High-precision resin (e.g., for medical models): Ra < 1 μm; formulated for minimal shrinkage.
- Flexible resin: Slightly higher roughness (Ra 1.5 μm ~ 3 μm) due to elastic properties.
(4) Post-Processing Processes
Post-processing is the final step to refine surface roughness—even a rough printed part can become smooth with the right treatments:
| Post-Processing Step | Roughness Reduction (Ra) | Cost Range (RMB/Piece) | Best For |
| Simple Cleaning (Isopropyl Alcohol) | 0.5 μm ~ 1 μm | 5 ~ 10 | Removes uncured resin; basic smoothness |
| Sanding (1200 ~ 2000 Grit Sandpaper) | 2 μm ~ 4 μm | 20 ~ 50 | Eliminates layer lines; Ra drops from 5 μm to < 1 μm |
| Polishing (Polishing Paste) | 0.3 μm ~ 0.5 μm | 30 ~ 80 | Mirror-like finish; ideal for jewelry |
| Secondary UV Curing | 0.2 μm ~ 0.5 μm | 10 ~ 30 | Reduces stickiness; improves surface uniformity |
| Spraying (Clear Coat) | 0.5 μm ~ 1 μm | 40 ~ 100 | Fills micropores; adds protection |
3. Surface Roughness Standards for Practical Applications
Different use cases require different levels of smoothness. Below are common applications and their recommended roughness:
| Application Type | Required Roughness (Ra) | Post-Processing Needed? | Key Reasoning |
| Basic Prototypes (e.g., part fit checks) | 2 μm ~ 5 μm | No | Smoothness isn’t critical; saves time/cost |
| Aesthetic Parts (e.g., custom figurines) | 1 μm ~ 2 μm | Yes (Sanding + Polishing) | Visible surface quality matters |
| Medical Models (e.g., dental crowns) | 0.5 μm ~ 1 μm | Yes (High-Precision Polishing) | Prevents bacterial growth; ensures biocompatibility |
| Jewelry (e.g., pendants) | < 1 μm | Yes (Polishing + Clear Coat) | Mirror finish enhances appearance |
| Functional Parts (e.g., small gears) | 1 μm ~ 2 μm | Yes (Sanding) | Reduces friction; improves part longevity |
4. 5 Step-by-Step Tips to Improve Light-Cured Surface Roughness
If your parts are too rough, follow these actionable steps to optimize smoothness:
- Choose the right technology: Use industrial-grade SLA or 4K DLP for Ra < 1 μm; avoid low-resolution DLP machines for high-detail parts.
- Set thin, but not too thin, layers: Start with 0.05 mm layers (balances smoothness and speed); use 0.025 mm for critical parts.
- Select low-shrinkage resin: Opt for dental or high-precision resin instead of general-purpose resin to reduce surface warping.
- Master exposure time: Test 3–5 exposure times (e.g., 4s, 5s, 6s) to find the sweet spot—avoid under/overexposure.
- Invest in post-processing: For Ra < 1 μm, sand with 1200 grit sandpaper, then polish with a microfiber cloth and polishing paste.
Yigu Technology’s Perspective on Light-Cured Surface Roughness
At Yigu Technology, we believe balance between precision, cost, and application needs is key to managing light-cured surface roughness. Many clients overspend on ultra-thin layers or expensive post-processing when their parts don’t require it—for example, using 0.025 mm layers for basic prototypes (unnecessary for Ra 2 μm ~ 5 μm). Our team helps clients match parameters to their use case: for dental models, we recommend industrial SLA + low-shrinkage resin + high-precision polishing (achieves Ra 0.5 μm ~ 1 μm); for prototypes, we suggest 0.1 mm layers + no post-processing (saves 30% ~ 50% of time/cost). We also provide resin testing kits to let clients compare shrinkage and roughness before full-scale production—ensuring they get the right smoothness without overpaying.
FAQ
- Can DLP ever be smoother than SLA for light-cured parts?
Yes—high-resolution 4K DLP machines (with pixel sizes < 0.01 mm) can reach Ra ~ 1 μm, matching mid-grade SLA machines. However, industrial-grade SLA (with smaller laser spots) still outperforms DLP for ultra-smooth surfaces (Ra < 1 μm).
- Why does overly thin layer thickness (e.g., < 0.02 mm) increase roughness?
Thinner layers require more frequent resin refilling, which can cause uneven resin levels across the build plate. This leads to inconsistent curing and visible surface defects, pushing Ra up by 1 μm ~ 2 μm compared to 0.025 mm layers.
- How much does post-processing (sanding + polishing) reduce roughness?
For a part with initial Ra 5 μm (from 0.1 mm layers + general resin), sanding with 1200 grit sandpaper can drop Ra to 1 μm ~ 2 μm. Adding polishing paste further reduces it to < 1 μm—total roughness reduction of 80% ~ 90%.