When should you use resin 3D printing?

Resin-based 3D printers, particularly those utilizing digital light processing (DLP) and stereolithography (SLA) technologies, are steadily becoming more popular and accessible. While there are advanced prosumer-level models like the Formlabs and Prusa SL1, newcomers to additive manufacturing can find budget-friendly options like the Elegoo Mars or Anycubic Photon for just a few hundred dollars. Additionally, a variety of printers and resin types are readily available for ordering, making it easier than ever to dive into this fascinating technology.

Resin items can look amazing, so when should you upgrade to one?

To know this, consider the following things:

The resin printing process is not similar to filament printing. The flow of design, pre-processing and post-processing is very different. Resin printing has a different workflow, with consumables and costs adjacent to resin.

Correct model for printing

FDM printers deposit molten plastic with a hot nozzle, while SLA/DLP printers use an ultraviolet light source to turn liquid UV resin into a solid. Both build a three-dimensional object layer by layer, always building the next layer on the foundation of the previous one.

So far they are the same, but in practice they have very different workflows and produce different results and are therefore good at different things.

This means that when it comes to good design, what’s intuitive for filament printers doesn’t necessarily apply to resin printers.

For example, when 3D printing resin:

The print size is small

Compared to FDM printers, resin build platforms can seem extremely small. The cheapest SLA printers have build platforms that are about the size of a cellphone screen.

The model is subjected to pressure between each layer

A “peeling” process detaches the model from the build platform after each layer, and the model must resist this. Each new layer must rest on a solid foundation, and the best way to ensure a good foundation is with supports. A model orientation that provides a minimum cross section (and therefore minimum area per layer) will reduce peeling forces.

«rafts» and the existence of several supports are the norm

With FDM printing it is often possible to avoid supports, but not with resin. The supports provide overall structure and strength to the model by being subjected to forces that FDM prints are not subjected to. Rafts and stands are the norm, not the exception.

There is virtually no tolerance for ledges and bridges

Compared to FDM printers, resin printing does not seem to tolerate excesses. With FDM, an unsupported overhang can result in a dropped edge or poor surface quality, but with resin printing the unsupported part is more likely to break or float (or get stuck on the build surface), contaminating the resin and interfering with the print. A model orientation that makes changes in levels as gradual as possible will minimize overhangs and therefore minimize the need for supports.

Resin printing requires more extensive post-processing

Prints should be rinsed of untreated resin by washing with isopropyl alcohol and allowing to dry. After that, they may eventually require exposure to UV light for further curing (more on that in a bit).

Pay attention to the «cups» and «islands» when orienting your models

Cups are tubular parts of a model that can create a suction force on the built surface during the removal process. This suction can weaken or distort ongoing printouts. Cups are avoided by providing drainage holes or other clear spaces to avoid any potential aspiration.

Islands are parts of a pattern that start apart from each other but join together later during printing. With resin printing it is best to avoid them, especially if they are thin or long, or if the piece has specific dimensional requirements. Tall or thin islands do not have the stable base of the rest of the model, and because they are printed and peeled off over and over again, they can move easily. By the time they join the model, they may not be as accurate as expected (assuming they don’t break first)

Handle the resin (and unrinsed parts) with gloves

All operations involving untreated resin should be performed with gloves (and ideally with eye protection). If resin comes into contact with your skin, wash it immediately with soap and water. Most prepress template adjustment functions will primarily consist of finding an optimal template orientation that balances the need for one support with the desire to minimize post-processing burdens caused by multiple supports.

How does the workflow differ from FDM?

Differences between filament and resin printers:

Pre-processing:

Choose a model orientation that offers a good balance between a manageable number of supports and a structure good enough to resist detachment forces. Avoid cups, ledges, unsupported bridges and islands.

Try to place as many details and surfaces as possible on the opposite side of the supports.

Printer Setup:

Prepare the print bed and build the tank. If you change resin types, make sure both have been cleaned first.

Pour the resin. Avoid exposing the resin to light. Wear protective gloves and goggles, and follow all safety precautions (which generally boil down to «don’t leave resin on your skin, and if you do, wash it off immediately»).

Avoid mixing resin types, which may have different properties and exposure time requirements.

Post-print:

After printing, the part will appear as a hard plastic object dripping resin. Rinse the untreated resin by washing it with isopropyl alcohol and allow the part to dry. Some resins require additional curing after printing. This can be done with a DIY treat box or by leaving the piece out in the sunlight.

Remove the supports with knives (or break them if the surface finish is not important) then proceed with other post-processing actions such as sanding or painting. Getting close to the supports, especially in delicate areas, is a big problem. So I ended up making a tool to make them easier to remove.

TWO MORE notes regarding materials and general workflow: ventilation and temperature

Ventilation is helpful for the printing and handling area, as some uncured resins have a sort of strong, acidic plastic odor (although standard Formlabs resins do not have any specific odor. Additionally, standard Formlabs resins do not require any additional post-print UV curing).

Temperature has an effect on the curing time of resins. The colder the resin, the slower it cures. Tankless printers built with controlled temperatures (i.e. all the cheap ones) should benefit from a work surface kept at a stable ambient temperature to achieve consistent results.

When it makes sense to print with resin

It makes sense if you are ready to accept the following:

The print surface will limit you to small items.

Setting up, maintaining, and using such a printer can be complicated and require gloves.

Ventilation is good due to the smell of some resins and the need to wash finished prints in alcohol.

Consumables do not only include resin and alcohol for washing parts. The construction surface of the tank must also be replaced periodically. For those who print only as a hobby, it is a thin plastic film, like a drum head. With Formlabs printers, it’s part of the build tank.

The process of setting and cleaning the resin must be done regardless of the size of the project, so it is more efficient to print in batches rather than batches few and far between. Resin also has a limited shelf life, so resin placed in a build tank should be used as soon as possible.

If you can get beyond these details, take advantage of the economic benefits that resin printing offers, because when parts come out well, they can look great.

Keep in mind that a resin printer cannot replace a filament printer as they are different tools suited to different things.