Disclaimer: This information was correct as of January 2023, but may not be true anymore. Use this as a guide for how to think about the problem, not what to buy.
Based on past experience and a lot of recent research, this is my best analysis of how you could assemble a print farm specializing in resin. I’m assuming you have between $5-10k, and you wish to support high-mix low-volume production (i.e. a university/school lab).
Selecting a Resin Printer
There are three basic technologies that resin printers are based around: SLA, MSLA, and DLP. In detail:
- SLA is stereolithography, which is the FormLabs-style laser-and-galvanometer printer. These printers can print any resin material, including fancy surgical and dental parts, but come at a tremendous cost (starting at about $2000/printer). Because the laser sweeps across the perimeter of the part, these tend to provide incredibly smooth, continuous edges.
- MSLA is “Masked SLA”, more commonly known as LCD printers because they use monochrome LCDs to mask a UV light source. The chief advantage of these is that they dirt cheap, with new printers coming in under $150. The chief downside is that LCDs only transmit a small portion of the light source, so these printers print incredibly slowly.
- DLP is Digital Light Processing, which is essentially a dense array of microscopic mirrors that reflect light (rather than masking it). This transmits most of the light, and so DLP printers are incredibly quick; for some geometries, even quicker than SLA printers. The trade-off is that DLP screens have discrete pixels leading to voxels that you can feel (with certain resins.) This is mitigated by selecting resins appropriately. DLP printers are priced comparably to mid-tier MSLA printers, but there are very few such printers currently on the market.
On balance, I’d recommend 3-6 DLP printers as the workhorse of your farm, and a single large-size MSLA printer for large jobs.
The only hobby-grade DLP printer currently on the market is the recently introduced Anycubic Photon D2. (Do not buy the Anycubic Photon Ultra, it is being discontinued.) Photon D2s are under $600/pc, so even on the lower end of the budget you could easily purchase five of these to start. The build area is about 130mm x 70mm x 165mm (5.1” x 2.7” x 6.5”). The printer has an expected lifespan of 20,000 hours, corresponding to about eight hundred meters (half a mile) in cumulative printed height.
For the large printer the Anycubic Photon Mono X 6K seems to be a good choice, costing about $500/pc. The print area is large, at 245mm x 197mm x 122mm (9.6” x 7.8” x 4.8”), but it prints about a quarter the speed as the DLP printer.
(I don’t have any relationship with Anycubic, their printers are just very highly reviewed.)
When hobby-grade printers were first introduced, there were only a few available resin types (with poor mechanical properties) available, but this is no longer the case. Advances in resin chemistry have greatly improved mechanical properties of resin. That said, absolutely avoid water-washable resins for now.
Manufacturers tend to describe their engineering resins with words like “ABS-like”, “tappable”, etc. Resin descriptions don’t adhere to any sort of standard, so don’t expect consistency across manufacturers. Other things to keep in mind is how different the shrinkage is between similar-sounding resins from different manufacturers.
- Engineering Resins: After trawling through many reviews, I’d recommend Siraya Tech’s Tappable ($37/kg) or Blu resin ($40/kg, biocompatible!) for a daily driver resin. Other highly-reviewed resins are AnyCubic, SUNLU, or ELEGOO’s ABS-Like ($30/kg).
- Flexible Resins: I’d also recommend keeping some of Siraya Tech’s Tenacious resin ($50/kg) on hand for flexible prints. It has the interesting property that you can mix it into many other regular resins to make them tougher and slightly flexible.
- Decorative Resins: Anycubic makes a DLP Craftsman resin ($40/kg) to mitigate the voxel effect from DLP resins; these are highly reviewed and make gorgeous parts. If this is not a concern, then SUNLU, ELEGOO 8K, AnyCubic, etc. all make cheap ($25/kg) and reasonably good resins.
- Specialist Resins: Don’t actually buy this, but you can get DLP-printable surgical-grade resins for $150-$300/kg on eBay.
Most resin is only good for 1-2 years from production, so don’t keep a lot of resin in stock. Also, some resins are very sensitive to temperature – a swing from 70F to 55F is sufficient to change the cure time of each layer significantly enough to wreck a print.
Washing and Curing
Don’t get a wash-and-cure station from AnyCubic or any first-party manufacturer – those are anemic.
For washing, get multiple (sealable) plastic bins comparable in size to the print volume, and huge quantities of 99% isopropyl alcohol (IPA). The washing process should be:
- A sealable container with used IPA. Parts from the printers, once drip-dry, should be dropped into these containers and agitated by hand for a minute or two. As the color of the previous resins in the IPA may leech into the print, you will need one for each resin color.
- Pat dry with paper towels. The paper towels can then be left exposed to UV light for a few minutes before being discarded in the general trash.
- A smaller container with mostly fresh IPA for fine cleaning. Immerse this in an ultrasonic bath for 5-20 minutes (varies based on geometry) heated to 40C–50C. Ensure the container is sealed and the temperature remains below 60C – otherwise this may release a cloud of atomized IPA which is a fire and explosion hazard! (Vevor manufactures a 30L cleaner for about $300; ensure that it is large enough for your plastic bins.)
- Pat dry with paper towels, disposing as before.
- Cure the parts on a turntable ($15) and a 20W UV flood light ($20). That will complete the curing process in a couple of rotations.
If you wish to maximize the structural strength of mechanical parts, get a plastic tub, line the walls with reflective aluminum foil, and immerse the part in 60 degree celsius water while exposing it to UV light. You can heat the water with a sous vide heater, or just use the aforementioned ultrasonic bath.
With the printer, you’ll need these additional parts:
- Print beds. Keep a couple on hand – it is much easier to wash a part while it’s still attached to the print bed. These are very cheap from AnyCubic ($20/pc).
- Resin trays. Keep 1-2 spare per printer so you can dedicate each to a specific resin. These are interchangeable between similarly-sized printers, even across manufacturers. I strongly recommend the Sovol 3D vats because they come with volume markings and silicone covers. ($20/pc)
- FEP film. These need to be replaced about every 100-500 hours of printing, or after one bad accident. These are specific to the resin tray (because of the hole and mounting pattern). They are very cheap, so keep a dozen or so on hand.
You will also need:
- Plastic scrapers
- Gloves (in large quantities)
- 99% Isopropyl Alcohol (in oceanic quantities)
- Paint filters (disposable ones, 80-200 size)
And more things I can’t think of at the moment.
On Chemical Risks: All the chemicals used in these processes are not good for your skin. IPA is not toxic, but it will dehydrate your skin and (under regular handling) will cause your skin to crack. Resins are generally not toxic, but are mild irritants to regular skin, and prolonged exposure can make the irritation worse. You should have face shields or eye protection, and possibly an eyewash station (or eyewash attachment for a sink) because the worst-case scenario is an accidental splash into someone’s face.
On Isopropyl Alcohol (IPA): Isopropyl alcohol should be 99%. In a pinch you could use 91% IPA, and at worst you would use denatured alcohol (which is ethanol + methanol) but that is inferior. You will need 5-10x as much IPA as resin, so be prepared to purchase gallons of the stuff. There may be some special handling requirements for IPA in a university context. If you expose resin-soaked IPA to UV light, the resin will cure into a jelly trapping the IPA, and the resulting mess can’t be disposed of easily. If you wish to clean and reclaim the IPA, many open-source designs are available. Virtually all these rely on exposing the surface of the mixture to UV light and gently skimming the cured skin as it forms, releasing the IPA. A reasonable thing to do to extend the life of your IPA is to cycle the IPA first in the finishing bath and then move it to the initial bath. You may also wish to keep one pair of containers per type of resin to prevent resin color contamination.
I recommend investing in a heated cabinet to about 80-90F. All resins are sensitive to temperature, and for some this makes the difference between effortless prints and endless frustration. I’ve built these before – all you have to do is get a shelving unit, wrap it in plastic, and mount a space heater inside. The front can be a shower curtain. If you do this, I strongly recommend bolting down the heater so it cannot be knocked over accidentally.
And finally, you will need a closed, lightproof cabinet to hold resins and trays that are not in use. Get a regular cabinet and apply foam tape around the edges to keep the fumes in. Keep a set of pint-sized containers to temporarily hold resin poured out from a vat.