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Hi Dakka, I recently came into possession of 3 3D-printed tanks, and I was wondering what I need to do to them to make them ready for paint. Specifically:

1) Do I need to sand the surfaces to get rid of the slight ridges from the printing process? If so, what grain of sandpaper should I be looking for? Or will these lines not show up once there's paint on the model?

2) Is there anything different I need to use primer-wise? Or will normal spray primers that I use for other models work just fine?

I did not print these models myself, rather I bought them from a friend (and he didn't print them either, not sure where he got them). So I don't know what kind of printing material was used, if that makes a difference.

Depends on how much effort you're willing to put into the finished piece. You can prime and paint it as-is just like any other model, nothing special, but it will show the print lines. If you want it to look like a finished piece, you'll need some automotive filler-primer (not just sandable primer, look for the filler primer or builder-primer), some 400 grit sandpaper, and a bit of patience.

Not mine, but you can see the process on a Battletech dropship here:
https://hardwarestudios.co/gepard-build-log-p-1/

Badger also just came out with a new supplemental airbrush primer line called 3D Prime.

I can't link to it from here, but they had some pictures of it being used on Facebook and the results looked pretty good. It's a two-stage primer, first you put down a self-leveling sort of layer, then a top-coat layer that is likely pretty much the same as their usual Stynylrez.

Other than that, like it was said above, you can use a filler primer and sand it. Or sand it then prime it. It is hard to say definitely how it will look, because every printer, material and model will be somewhat different, depending on a variety of factors. But, with no prep work, they will probably be somewhat noticeable if it was printed on an FDM, but again, it is hard to say definitively.

It all just depends on how "good" you want the results to look. If the layer-lines don't bother you, just do your normal priming. If they do, it's up to you how aggressive you want to be in trying to eliminate them.

I picked up this stuff



I haven't done a great deal of painting of my prints yet, but a test on a failed print seems to look quite smooth after a bit of light sanding with a sanding sponge.

So, you should prime, then sand, then prime again? Sanding the bare plastic is a bad idea I'm guessing from this? Sorry if I'm asking silly questions here, but I have zero experience with 3D printed stuff.

You could sand it first, but you're essentially just making work for yourself as you'll be removing material that the primer would make unnecessary.

Also, don't be tempted to use any sort of mechanical assistance, like a Dremel or other sanding machine. Most 3D prints are made from PLA plastic which melts at a relatively low temperature. The friction will melt it in no time at all. Wet sanding by hand will avoid that and also keep any dust to a minimum.

The plastic is just harder to stand smooth..if you add a bit of softer filler material it just makes it easier.

 ZergSmasher wrote:
So, you should prime, then sand, then prime again? Sanding the bare plastic is a bad idea I'm guessing from this? Sorry if I'm asking silly questions here, but I have zero experience with 3D printed stuff.

It comes down to thickness of the material being greater than thickness of the gaps. Sanding the plastic is simply more work.

Liquid greenstuff is also very useful, as is milliput mush.

 ZergSmasher wrote:
Hi Dakka, I recently came into possession of 3 3D-printed tanks, and I was wondering what I need to do to them to make them ready for paint. Specifically:

1) Do I need to sand the surfaces to get rid of the slight ridges from the printing process? If so, what grain of sandpaper should I be looking for? Or will these lines not show up once there's paint on the model?

2) Is there anything different I need to use primer-wise? Or will normal spray primers that I use for other models work just fine?

I did not print these models myself, rather I bought them from a friend (and he didn't print them either, not sure where he got them). So I don't know what kind of printing material was used, if that makes a difference.

Well, it's really down to the quality of the print, tbh.

Something printed at a decent layer height with a well calibrated printer? You'll be fine with just priming:




If you go with a faster/higher layer print, thought? Well, that will be quite noticeable:



In these cases you probably should hit it with a filler and sand it down a bit so that it gets less noticeable.