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When printing a 3D model on a resin printer should I sand down imperfections and marks left by supports before or after curing?

What are the benefits and drawbacks of doing it either way?

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    $\begingroup$ how soft is your uncured print? does sandpaper sand it, or just mush the material around and clog the sandpaper ? $\endgroup$
    – Criggie
    Oct 11 at 8:58
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    $\begingroup$ It's soft enough to be easily scratched by accident, but 1000 grit does not clog. $\endgroup$ Oct 11 at 11:20
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Postprocessing AFTER Curing

Liquid or not fully cured Resin is a skin irritant and should not be handled without gloves. Exposure to it is to be reduced to an absolute minimum.

To make sure you work with an inert chunk, you need to first wash and then cure your items before handling any postprocessing, such as sanding. Only this way you can avoid getting in contact with any liquid resin in case any spot inside is not cured, possibly due to enclosed cavities or places that were not reachable by washing but which might be exposed during postprocessing.

As a side effect, abrasive post-processing works much more evenly, the less ductile and more even the material is. As an example, woods that have very hard and very soft rings interchanging, are a pain to sand smoothly without the aid of a contraption and do sand differently with than sideways to the grain, while even materials like steel file smoothly in all directions. A fully cured resin print is much more monolithic than a raw print.

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  • $\begingroup$ With a modern resin printer the models are semi cured upon printing. The resin is solid but soft and loses its irritant properties. It just needs a wash to clean off liquid resin. $\endgroup$ Oct 12 at 7:09
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    $\begingroup$ eh... no. If there is any bubble of uncured resin in the model, and you open that by sanding, you end up with a mess. THAT is why you cure before. $\endgroup$
    – Trish
    Oct 12 at 7:41
  • $\begingroup$ If something like that happens then you really should be looking at your print settings. That's absolutely not normal. $\endgroup$ Oct 12 at 19:11
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    $\begingroup$ It is not normal, but the basic laboratory and manufacturing rules say: better safe than sorry. I have gotten prints from a friend who thought he would do a favor by hollowing out the model and having the resin drain to reduce weight. Good idea generally. However, the hole clogged during washing and the center did not drain, and as a result there was uncured resin coming out from them when I opened up a hole to mount another part. Things like that are why you want to cure through before any postprocessing. $\endgroup$
    – Trish
    Oct 12 at 19:39
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    $\begingroup$ @AaarghZombies Something that is soft is hard to sand, so make it as hard as possible for abrasive post processing. E.g. vibrating disc saws do not cut your skin, but work fine on wood and metal. $\endgroup$
    – 0scar
    Oct 15 at 21:07

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