As I learned after asking about the chemistry of a 3D printing Resin, the material uses radical polymerisation to get a well connected, branched copolymer. It is comparable to resin cast material but more brittle. So let's look, akin to the PLA-gluing question, what we can do!
Step 0: Safety First!
Some of these methods are working with chemicals that can irritate the skin (resins, cyanoacrylate) or have irritating or flamagle fumes (heated cyanoacrylate).
Use proper protection when working with these! Eye protection and respiratory protection, as well as gloves, are to be used when necessary. Read the manual of the products you are working with!
For most glues, it is advisable to prepare the surface: very lightly sand it to increase the surface area, don't touch the prints with bare hands to prevent fingerprints etc. Follow the manual!
As a result of the chemistry I would suggest the following glues:
- The resin itself! Carefully applying a thin layer of the printing resin onto the cured parts and then pressing the parts together before letting it cure again will get you a good bond that might not even be visible as you have exactly the same material. Note though, that you might be able to assemble the part between washing and curing for absolute minimal visibility of the gluing surface and maximum bonding. Also note, that for a non-transparent resin (fully opaque to 400 nm light) you'd better look for a different gluing system, as the bond will be much weaker if it can harden only at the edge.
- Cyanoacrylate, aka Superglue. This glue is pretty much a one-serves-all, though it might cloud your surface. Also, not all superglues are the same, and some might work better than others or store differently.
- Together with talcum powder, CA glue can fill gaps easily.
- CA is not stable under heating and when heated too much, if breaks apart into a rather noxious fume!
- 2-phase epoxy or polyurethane. Another glues everything category, that should work rather well. The epoxy bonds are harder, the polyurethane ones are a little more flexible, but both bond very well with cured resin. As resin prints don't really deform under heat, you might take even faster-curing types.
- 2-phase Putty - in a similar vein come 2-phase putties like Green Stuff or Miliputt, which harden after mixing. Their heat generation isn't too big and they allow to fill gaps easily. My favorite stuff though is not the expensive modeling putty but the stuff from the home depot: stuff like Pattex Repairsorry, no English site for this or UHU Repair All Powerkitt harden within an hour, are surprisingly cheap and get a smooth surface.
Unlike PLA, we can not use thermic methods to add inserts, friction-weld or weld/solder two parts together as Resin prints are generally not thermoplastic.