Location
Mount Vernon, WA 98274
Subtractive manufacturing has long been the hallmark of precision, but modern workshops are finding strength in marrying additive and machining techniques. Stereolithography (SLA) delivers unheard-of detail in small-scale components, while a desktop CNC micro-router or mill can refine critical features, smooth surfaces, and add threads or bores with exacting tolerance. In this guide, we’ll explore how to use SLA resin printing followed by CNC micro-milling to craft parts that look and perform like shop-machined metal.
We’ll cover each step in the process, point out tools and tooling options that make the difference, and highlight tips and pitfalls so you can get started without guesswork. By the end, you’ll have a clear workflow for turning raw resin prints into finished, functional pieces-perfect for prototyping jigs, precision enclosures, and decorative objects with mechanical features.
Digital Model Preparation and Slicing
Every successful part begins in your CAD or 3D modeling software. When designing for SLA, factor in minimal wall thicknesses (usually 0.6-1.0 mm depending on resin properties) and gentle tapers on overhangs. If you plan to machine flat surfaces or add bores, orient them parallel to the build platform so the milling tool can access them without collision.
Export your model as an STL and import it into an SLA slicing utility. Set layer height between 25 μm for ultra-fine detail or up to 50 μm for faster print times with acceptable surface quality. Adjust exposure time based on the manufacturer’s resin data sheet-accurate timing reduces overcure and preserves small features. Position the part to minimize supports on critical faces; a few well-placed support sticks are worth the extra cleanup versus trying to machine over support scars.
SLA Printing and Resin Selection
Select a reliable desktop SLA printer with a stable Z-axis and consistent light source-stability is key to repeatable tolerances. Choose a resin formulated for toughness or flexural strength if you expect mechanical use, or a high-viscosity engineering resin for heat resistance. Keep ambient temperature between 20-25 °C to ensure uniform cure.
After slicing, start the print and monitor the first few layers for proper adhesion. If you see peeling or warped corners, adjust build plate leveling or reduce lift speed between layers. A smooth print surface requires well-maintained vat film and a clean optical window-inspect these regularly under good lighting.
When the build completes, remove the part carefully. Wear nitrile gloves and protective eyewear-uncured resin can irritate skin and eyes. Use a plastic scraper to avoid scratching the surface, and transport the fresh print to a wash station.
Post-Processing: Cleaning and Curing
Submerge the print in isopropyl alcohol (IPA) or a dedicated washing solution for two to five minutes, gently agitating to remove uncured resin. A dual-stage wash station speeds this up by circulating solvent without manual handling. Once clean, let the part dry thoroughly before moving to the curing chamber.
Position the part on a rotating tray under UV LEDs at 405 nm. Follow resin guidelines for time-often 5-10 minutes per side. Rotating the piece exposes all angles and prevents uneven hardening. A well-cured part will have a consistent rigidity and will no longer smell of resin.
Inspection at this stage is crucial. Look for surface blemishes, support marks, or slight warping. Your CNC micro-milling step will remove small imperfections, but larger distortions may require reprinting.
Setting Up CNC Micro-Milling
With a clean, cured print in hand, bring out your desktop CNC machine with a micro-milling spindle. Secure the part in a low-profile vise or with soft jaws to avoid crushing delicate geometry. A spoil board or sacrificial layer prevents stray milling marks on your machine table.
Choose a ball nose or tapered end mill in carbide, ideally 0.5-1.0 mm diameter for fine detail. Adjust spindle speed to around 15,000-20,000 RPM, and set a shallow depth of cut-0.1-0.2 mm per pass-to prevent chipping the resin. Use air or gentle mist cooling to clear chips and reduce heat buildup, which can soften the resin.
Generate your milling toolpaths in CAM software, focusing on areas that need smooth flat surfaces, crisp edges, or precision bores. Add chamfers or fillets in toolpaths to remove print layer lines. For round holes, use a small-diameter drill bit or boring tool and slow plunge speeds to avoid cracking.
When the machine is ready, run a dry test pass above the part to confirm clearance and zero points. Then execute your finish passes. Listen for consistent chip formation-tiny uniform flakes mean your feeds and speeds are dialed in. If you see long strings or burning odors, back off feed rate or increase coolant flow.
Quality Checks and Finishing Touches
After milling, inspect the part under a magnifier. Measure critical dimensions with calipers or a miniature micrometer to verify tolerances. If you need welding holes or threaded inserts, a small tap can cut threads cleanly in the resin. Seal any tapped holes with a thin coat of epoxy if extra strength is required.
For the smoothest surfaces, lightly polish with micropolishing compounds or 800-1200 grit sanding sticks. A fine buffing wheel can remove tool marks but proceed gently-over-polishing can dull sharp details.
Finally, apply a thin clear coat or matte varnish to protect the surface from UV and moisture. This layer also hides any remaining print lines and gives professional consistency to parts used in prototypes or final assemblies.
By combining the high resolution of SLA printing with targeted CNC micro-milling, you unlock a new level of detail, accuracy, and surface finish. This hybrid approach is perfect for small batch production, precision fixtures, medical models, and scale prototypes where every micron and edge count.
Embrace the workflow, tweak settings to your materials and machine, and soon you’ll produce parts that stand toe-to-toe with shop-machined components. Patience and iteration are part of the craft: each pass of the router cuts away imperfections, revealing the design you envisioned from raw resin to refined reality.
Beyond the Guide
Now that you’ve walked through model prep, SLA printing, curing, micro-milling, and finishing, take time to experiment with different resins, tool geometries, and cutting strategies. Share your findings with the community, adapt the workflow to new materials like ceramic-filled resins, or explore multi-axis machining for even more complex forms. The frontier is wide open when subtraction meets addition.
