Prepping a 3d print for painting

[Glitchinthesystem]

Very new to the use of 3D models but from what I can determine on this forum the consensus to prepare a 3d model for accepting paint i.e. getting the surfaces smooth is approx. as follows:-

• Wash in water and liquid soap
• Degrease with IPA
• Apply an automotive filler primer
• 240 grit wet sanding
• Rinse and repeat until it starts looking smooth
• red oxide plastic primer
• 400 grit wet sanding until desired finish is achieved.

However has anybody used an Etch Primer before applying a filler primer to aid adhesion ?

[Tiger6]

Etch primers are for metal parts, they won't have any effect on plastics. What you could use instead is an 'adhesion promoter', these are available as spray cans from places like Amazon, and can be useful with shiny plastics like PETG.
Washing your parts under the tap is a good idea if you use PVA glues on your build plate, but 'degreasing' sounds a bit OTT?

[Glitchinthesystem]

Etch primers are for metal parts, they won't have any effect on plastics. What you could use instead is an 'adhesion promoter', these are available as spray cans from places like Amazon, and can be useful with shiny plastics like PETG.
Washing your parts under the tap is a good idea if you use PVA glues on your build plate, but 'degreasing' sounds a bit OTT?

Thanks that's the sort of advice I wanted and appreciate, I should add I'm not printing the parts (it's a purchase from a seller on Ebay), but I will ask him what materials he has printed the kit in though.

[tankme]

If the kit is going to spend time outside it should probably be printed in PETG, ABS, or ASA. PLA has been known to warp in the sun. It has a very low "glass transition temperature" which doesn't mean melt, it means deform. I have personally had PLA parts shrink and warp in the sun. I would also skip the degreaser step as it's probably overkill. Plastic is porous and some of them are affected by IPA. If you want to clean before priming, use mineral spirits. Depending on how rough the surface is, I will sand before priming to get rid of the huge layer lines as primer won't cover those up. Putting primer on huge layer lines is just wasting primer IMO. In the case of tanks and military vehicles, they typically don't have show car paint finishes so a few nicks, or dents, or defects in the paint are very normal. It doesn't have to be perfect.

[50koruny]

Instead of the huge amount of the filler, you can use XTC-3D.
Its a special epoxy for the 3D printed parts.
It's not the cheapest, but in the end it costs less than the filler.
It takes a bit of practice, but it's worth it.

Anyway, as Tankme mentioned - my advice is to avoid models printed from PLA.
All it takes is direct contact with the summer sun and it's over.

[tankme]

I've used the XTC-3D. To me it dried way to quickly and ended up wasting some of it. I'm going to experiment with some UV resin also.

[50koruny]

Yes. It dries relatively quickly.
Especially if you mix a lot of it at once.
Anyway, when it starts to dry, you can dilute it with spirit (Technical alcohol?I dont know what is the accurate name of this thing in English).

I'm not saying it's not complicated...
Anyway, with a bit of experience and practice, it's the best possible way to smooth out the layers after 3D printing.

I've tried UV resin, but I don't trust it very much.
I'm not sure what it will look like in say 5 years.
I go outside a lot with my models, and the sun would affect the resin in a way that would constantly cure it.

When I print resin on RC models, I use varnish with a UV filter to keep the parts from degrading in the sun.
Applying this to the whole model would be quite expensive.
Especially in the 1/6 scale.

[jee]

I think spirit would be referred to as IPA

[Styx 2022]

Just to add to the debate here is my method on prepping 3D printed models for painting :-
I do nothing !
On the Comet I printed it, assembled it and then sprayed it with Vallejo Surface primer.
There was no washing, filling or rubbing down.
My thoughts are that if it is 3D printed then it should look like it is 3D printed.
You don't make a Lego tanks and then round of all the corners.
This is my own personal preference and I fully appreciate other peoples views.

[50koruny]

I think spirit would be referred to as IPA

No.IPA is different.
I mean the most ordinary technical alcohol.

Just to add to the debate here is my method on prepping 3D printed models for painting :-
I do nothing !
On the Comet I printed it, assembled it and then sprayed it with Vallejo Surface primer.
There was no washing, filling or rubbing down.
My thoughts are that if it is 3D printed then it should look like it is 3D printed.
You don't make a Lego tanks and then round of all the corners.
This is my own personal preference and I fully appreciate other peoples views.

Interesting opinion.I have not come across such an opinion before.
Most people are bothered by the layers.
And I'm the most extreme case of this approach.
I always try to hide all the layers as much as possible.
I'm obsessed with making them all disappear.

But in no way do I mean to say that your approach is wrong or that I disagree with it.
Everyone has their own tastes and does what they like and that's the way it should be.