3D printed models

[Dobber]

I’m new to the world of 3D printed models. I have a couple of questions:

1) Do they need to be washed before priming, they way a Resin kit does?

2) Do they sand well? Or will it require a course sand paper?

Thanks

Chris

[SpaceRanger1]

Here's some advice from the "Model Monkey" website (https://modelmonkey.wixsite.com/modelmonkey; Model Monkey designs and sells Shapeways 3D printed parts for model warships):

2. What kind of glue should I use?
Choose a glue that is specifically intended for the material your model is printed in. For "Frosted Detail" plastic, Cyanoacrylate (CA) "superglue" works best. But please be aware that superglue remover can melt the plastic. Testors liquid or tube cement won't work. Testors cement works best for polystyrene plastic but these 3D-printed parts are made of either acrylic plastic or nylon.

3. Should I clean the parts before painting?
Leave your parts in the plastic bag, uncleaned, until you need them. Clean your parts with a mild water-based detergent like "Dawn", "Fairy", "Neophos", "Sun", "Sunlight", "Joy", or "Vim" dishwashing liquid, baby shampoo (no conditioner), or "Simple Green" using an old, soft toothbrush, Q-tips or pipe cleaners. Do NOT use any cleaner, primer, paint or thinner containing acetone, acetate or methyl ethyl ketone (MEK). Frosted Detail plastic may be sensitive to prolonged oxygen exposure. Paint your "Frosted Detail" products soon after cleaning them.

4. I heard that I have to sit the parts in sunlight for a while before I paint them. Is that true?
Yes, for products printed in "Frosted Detail" acrylic plastic and "Black High Definition Acrylate" plastic. During the printing process, liquid resin is hardened by ultraviolet light. Microscopic bits of resin may remain unhardened. Let your parts sit in direct sunlight or under a UV or fluorescent lamp for several hours to fully chemically harden the resin. The parts will appear a translucent white when fully hardened. Heat will not harden the resin, only UV light does. UV light breaks down an inhibitor in the liquid resin allowing the resin to harden.

5. The surfaces are rough. How can I smooth surfaces without harming detail?
After your parts have fully cured, if desired, careful use of an inexpensive "air eraser" emitting common household baking soda as a gentle grit can help smooth surfaces and remove any unwanted "frost" without harming detail. Air erasers, like an airbrush but much cheaper, can be found on Amazon.com or directly from the manufacturer. Models by Harbor Freight and Paasche are popular. For those few products printed in "Strong and Flexible" plastic, a kind of nylon that is difficult to smooth, apply thin layers of primer meant for nylon, allow the primer to harden, then smooth the hardened primer.

6. What kinds of primer and paint should I use?
For "Frosted Detail" acrylic plastic, acrylic primer and acrylic paints meant for plastic are recommended. Any unhardened resin in the plastic can chemically react with enamel paints preventing the paint from hardening. If you prefer enamels such as "Colourcoats", enamels can work but extended exposure to ultra-violet (UV) light before painting is critical. Make sure you sit your parts in direct sunlight or under a UV lamp for several hours to fully harden the plastic before painting.

For "Strong and Flexible" products, only primers and paints intended specifically for use on nylon should be used. Other hobby paints may not adhere. Simply Google "primer for nylon" and "paint for nylon" for several good choices.

7. I like to use an airbrush. Will thinners harm the plastic?
They can if the thinner contains strong chemicals. Acetone will melt Frosted Detail plastic. Do NOT use any thinner containing acetone, acetate, or methyl ethyl ketone (MEK). Acetate is found in acetone-free nail polish remover. Acetate and MEK can cause a crystalline powder to form on the surface, even after painting, which is an annoyance to remove. The following chemicals may cause crazing, cracking, discoloration, or dissolving of Frosted Detail acrylic plastics: Acetic Acid, Acetate, Acetone, Ammonia, Aromatic Solvents, Benzene, Brake Fluid, Butyl Alcohol, Chlorinated Solvents, Disinfectant, Ethyl Alcohol, Goo-Gone®, Kerosene, Lacquer Thinner, Lestoil® Cleaner, Lysol® Spray, Methyl Ethyl Ketone, Naphtha, Pinesol® Cleaner, Sulfuric Acid, Turpentine, Toluene, White Cap® Cleaner, and Xylene.

[TazMan2000]

It depends on the material that is beings used to print. PLA is biodegradable, but a quick wash in alcohol probably is a good idea, as well with ABS.
in my experience, PLA is crappy to sand, but ABS is less so. The amount of sanding required is dependent on the quality of the printer and layer thickness.

TazMan2000

[TooOld4This]

Well in MY experience, just paint them after super gluing any parts together, they don't use mold release agent, and I've never had any problems with paint adhering to them.

[DeltaVee]

I've never washed and had issues on only 1-2 with paint not sticking readily.
Gunze Mr. Primer Surfacer spray can. Either 500 or 1000, depending on the part's detail and how much filling you need.
After that, you can paint with almost anything.
Nylon sands like rubber... not well.