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I'm considering getting a SLA 3D printer, but the big uncertainty is whether I can build large things like propellers by printing them piecewise and fusing them together like you can with ABS and acetone (or butanone).

The resins are proprietary, so I guess that's why I can hardly find any information on this. But according to Wikipedia, photopolymers are thermoset, so that rules out melting them. But are there any solvents that can fuse them?

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  • $\begingroup$ You should ask the manufacturer. $\endgroup$ – Eric S Jan 7 '17 at 14:03
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No such luck: the UV-curing resins used in SLA and polyjet printers aren't thermoplastics. These are cross-linked polymers.

On the other hand, polyjet materials and SLA can be bonded with epoxy or cyanoacrylate glues.

As an aside, I wouldn't try to make a functional propeller out of SLA material, because it's fragile. You could, however, use the SLA print as a master for a mold. A cast urethane propeller would be considerably stronger than an SLA.

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  • $\begingroup$ I never knew polyurethane could be cast at room temperature. Thanks for the tip. I'm wary of using epoxy or cyanoacrylate because I don't know if the bond strength will be as good as the 95% achieved with solvent welding (maybe with dovetailing or similar) $\endgroup$ – Yale Zhang Mar 7 '17 at 20:22
  • $\begingroup$ @YaleZhang: If you were to glue straight flat perpendicular surfaces as binding area, the bond would be a weak spot, but if you print keyed latches with some extra length-wise surface ( like so ), the glued bond will be as strong as corresponding thermal bond would be. $\endgroup$ – SF. Jun 7 '17 at 9:52
  • $\begingroup$ Also, construction grade PUR foam makes a quite neat, light, cheap, quick and easy - if rather weak - casting material. $\endgroup$ – SF. Jun 7 '17 at 9:55
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It will undoubtedly depend on the resins in use. I've found several forums which suggest that isopropyl will dissolve cured residue -- but not necessarily allow bonding/welding.

As you noted, since photopolymers change their chemical composition, you can't weld them. My strong suspicion is that the same holds for attempts at chemical dissolving, i.e. the cured material won't re-bond after a solvent destroys the molecular structure.
While lack of evidence is not evidence of lack, the fact that manufacturers of photopolymer material and 3Dprinters which use the material don't mention or sell any post-production bonding compounds certainly suggests there's no straightforward way to do so.

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Yes you can... theoretically

You are absolutely correct that most 3D printed materials will not work for this application but I did recently come across a 3D printable PVC that I believe you can melt together. I was looking into this for a project of mine because I wanted to 3D print parts and ultrasonically weld (melt) them together. I was in contact with a rep from 3D vinyl and they made it sound like a possibility, unfortunately for me my project changed directions and this rep disappeared but depending on your resources and exact needs I would say it is worth looking into

It is a very new product and I don't know what stage it is at but it looked promising to me

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  • $\begingroup$ Maybe you could bond the pieces together using extra resin and an intense UV lamp. $\endgroup$ – Eric S Apr 8 '17 at 13:29

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