Image

Design Guide

Stereolithography

Our design guidelines for Stereolithography (SLA) include important information to improve part quality, minimize costs, and reduce overall manufacturing time. By following the guidelines, you can produce high-quality parts, reduce expenses, and improve productivity.

If you have any questions regarding our design guidelines, you can contact our technical team by telephone, email or chat with us online.

Download Guidelines as PDF

Overview

Stereolithography (SLA) uses a UV laser to cure liquid photopolymer resin layer by layer into a solid part. The small laser spot size and layer height means that fine details can resolve very accurately.

Image
Maximum Build Volume
1500mm x 750mm x 550mm (59” x 30” x 22”)

SLA offers the largest build volume in our facility, capable of producing parts up to 59 inches long in a single build. Parts larger than this can be printed in sections and assembled.

Image
Tolerances
Standard parts (10" x 10" x 10" or smaller): ±0.25%, with a lower limit of ±0.25 mm
Large parts (10" x 10" x 10" or larger): ±0.4%, with a lower limit of ±0.5 mm

Tolerances as tight as +/- 0.15 mm (+/-0.005") can be achieved on request. If tighter tolerances are required, please provide an engineering drawing when requesting a quote.

Image
Layer Height
50 or 100 microns

Parts are printed at the standard 100 micron layer thickness (HD) unless our high definition (XHD) option is chosen, at 50 microns. Keep in mind that our higher resolution option also doubles the print time. 

Image
Surface Finish
High Definition 

Parts have a smooth and uniform surface finish. Very small layer lines may still be visible, especially on surfaces at a low angle relative to the build plate.

Wall Thickness

Large, thin-wall areas are at risk of deformation. In general, follow wall design rules for injection molding to achieve a more uniform and consistent part.


Image
Minimum Wall Thickness
0.8mm (0.031”)

Supported walls are connected to two or more sides and are thick enough to support the model.

Image
Minimum Unsupported Wall Thickness
1.5mm (0.059”)
Unsupported walls are connected on only one side or edge.
Image
Minimum Pin Diameter
2mm (0.07”)

The minimum pin size depends on a combination of parameters such as; part orientation, nozzle diameter, and length of the pin.

Minimum Detail Size

Intricate details and text are often the reason for choosing this technology over others. Try to place fine details away from overhanging faces that require support, since touchpoints can interfere with intricate geometry.


Image
Debossed Details
Minimum Width and Depth: 0.5mm (0.019”)

Engraved details are recessed features on your model. Making these too small can result in closed gaps and loss of detail.

Image
Embossed Details
Minimum Width and Depth: 0.5mm (0.019”)

Embossed details are raised features on your model. These usually resolve better than engraved details.

Image
Text
Minimum point size: 14pt

Bold, sans-serif fonts typically resolve better at smaller sizes.

Part Clearances

The mechanical performance of printed assemblies is sensitive to variables such as print orientation, layer height and machine tolerances. It is best to test and refine any mated parts before committing to a full production run.


Image
Minimum Clearance
0.5mm (0.019”)

Clearance is the distance between two moving parts on hinges, joints, mating parts, etc. We require a minimum of 0.5mm on all sides.

Image
Minimum Press Fit
0.1mm (0.004")

For a tight press fit, add a small offset, and chamfer the leading edge to ease entry. Always print an initial test part to dial in dimensions.

Image
Printed Linkages
Minimum: 0.6 mm (0.023")

It is possible to print mechanical linkages (eg. hinges, chains) already assembled. When designing for this scenario, clearance should be at least 0.6mm to prevent these features from fusing during the build.

Holes & Gaps

Hole accuracy can vary depending on print orientation, thickness of surrounding material and support structures. For tight tolerances, consider printing center marks and post-machining them instead.


Image
Minimum Hole Size
0.5mm (0.019”)

Depending on orientation, circular holes can resolve as ovals – if higher accuracy is required, printing the hole smaller and then drilling it out is recommended.

Image
Minimum Gap Size
0.5mm (0.019”)
Gaps or slots can fuse if made too narrow, and support material may be difficult to remove. If possible, orient gaps along the xy-plane for highest accuracy.
Image
Minimum Drain Hole Size
Minimum 4 mm (0.15”) to drain resin
Minimum 20mm (0.78”) to remove internal supports

Hollow features may be filled with uncured liquid resin as well as internal support structures. Any internal volumes in the part must include holes so that the support can be drained and flushed during post processing. Holes at opposite ends can significantly improve the flushing process. 

In order to remove internal supports, a larger hole is needed so that tools can enter the volume to remove supports. A plug can be designed to glue this hole shut after post processing.

Part Geometry

Part geometry can be optimized for 3D printing to reduce material usage, increase strength and rigidity, and take advantage of machine capabilities.


Image
Fillets

Fillets can be used to reduce stress concentrations and increase the strength of your part. 

When designing fillet features across inside and outside corners, it is best to have them share a common center point in order to maintain a consistent wall thickness.

Image
Bosses and Ribs

Bosses and ribs are an effective way to add strength and stiffness to a part while keeping material consumption to a minimum. This can also reduce build time and use less support material.

Bosses and ribs can generally be matched to part thickness or up to 0.5mm (0.2 inches) less.

Image
Support Structures
Thin supports are used to stabilize the part during printing. Supports are removed by our technicians and any remaining defects and are sanded down to leave no visible imperfections.
Image
Infills

Parts are always printed solid. Infills are not applicable for SLA.

Threads & Inserts

Large threads can be printed but they will not hold up to repeat use or much force, so inserts may be required. As a general rule, avoid printing hardware.


Image
3D Printed Threads

Coarse threads can be printed, but smaller threads may need to be tapped. Include a clearance offset when both male and female fasteners are printed.

Image
Tapping & Threading

Design parts with holes sized for tapping, or center marks for drilling a pre-tapped hole. You may need to reference a tap and drill chart to figure out which hole size corresponds to a given thread.

Tapping removes material, puts pressure on the surrounding geometry, and fastener locations are often points of stress, so make sure there is enough material surrounding the tapped hole.

Image
Inserts

Heatset inserts cannot be installed with photopolymers since they are thermoset plastics, so design holes such that inserts can be glued into place. 

Post Processing

While printed parts are highly functional and accurate, there are a variety of ways to modify them after printing to enhance durability or aesthetics.

Image
Sectioning, Joining, and Bonding

Parts too big to fit on the print tray can be split in CAD and printed in multiple parts, then glued or press fit.  Use joinery features, such as tongue and groove, to ensure the sections are aligned and bond tightly. 

Depending on orientation, material and other properties, an offset may be required to make sure the parts fit together properly. We recommend printing a small test part to dial in the offset before printing the full set of parts. 

Image
Post-Machining
Parts can be machined to tighter tolerances using traditional or CNC subtractive manufacturing equipment.
Image
Coatings

SLA parts have an ultra smooth surface finish and can be easily sanded, primed, and painted to achieve an excellent surface finish. Parts can also be dyed at low temperatures using synthetic dyes.

Image
Vapor Smoothing

Not applicable for SLA.