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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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.