Tutorial Index Who can make a Tutorial? A: Anyone How do I make a tutorial? A: Create a thread in any part of the forum you think your tutorial pertains to such as Costume, Props, Soft Parts etc. How do I get the tutorial in the Tutorial Section? A: start a conversation with me or any staff…
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As for your specific questions:
There are as many ways to smooth 3D printed Parts as there are members here, and everyone has their preferred method and process. Many of these are covered in the Tutorial Index.
It is possible that your issues 1 and 3 are related. When you say Filler Primer, are you talking about an aerosol/rattle can/spray Filler Primer, or do you mean Spot Putty? For the spray paint version, you want to make sure that the can is thoroughly shaken and mixed, warming the can in a bath oh hot water or running it under a hot tap can also help with a smoother application, and do light, smooth passes, applying thing coats from a distance of 6 to 10 inches. For filler or spot putty, you want to apply it in thin coats and allow it to thoroughly dry and off gas, otherwise the acetone that is the thinner in the material will still be present and will cause issues with paint.
The parts of the print that are having noticeable paint adhesion problems, are they bottom parts of your piece that were in contact with your bed, and do you use any extra product to attempt to promote bed adhesion, like a spray or glue stick? Some people do, and these adhesives can cause issues with paint adhesion. Washing your piece with soap and warm water, and then allowing it to thoroughly dry can give you the best surface for paint adhesion.