3D printed loco bodies

[Stefan Krebs]

Dear Hobby,

Yes, I fully agree, and it was the only reason for me to cough up the asking prices of Arsenal M; I was in the Civil Defence, and they produce some obscure models, e.g. Tempo Land Rover and Menck Schuerfkuebelraupe, that are extremely unlikely to appear as injection moulded model, but I absolutely wanted.
And that's where the strength of 3D-printing lies: prototypes and small number batches, where the cost for the expensive moulds would drive the price per piece to prohibitive levels. NPE does comparable models in injection moulding, and their price is 2,5 times higher!

You decide where to compromise: detailing and surface versus price.    :laugh:

With regards to painting:
I recollect, we had extensive discussions and arguments over 35 years ago at university, and to prove the point I assembled some Rai Mo kits (some of which are all polystyrene plastic, some white metal and polystyrene), and painted them to match the (then new) Trix Bavarian range. It proved that you can achieve a paint quality to match commercial products even with waterslides. It also proved that you can't identify the base material through the paint job, if that job is done well. I used semi-gloss clear varnish ex spray can thinly, and the finish was exactly as Trix's.

However, 15 years later that varnish had yellowed, or rather browned, and that showed even the slightest thickness variations of the coat! No, they weren't exposed much to sunlight.
Redone with a spray-gun and top of the range varnish from Tamiya.

Cheers
Waldschrat

[Graeme Dunbar]

I read somewhere that a single coat of gloss at 00 scale is like having 76 coats of clear varnish on your prototype.

I've sometimes wondered how that observation came about and why it is used?

In one respect it is literally true (or more precisely a single coat is like 76.2 coats, or 87 if it happens to be HO), though assume that is not what is implied. That is possibly taken in conjunction with information that achieving a high gloss on railway carriages requires several coats (and rubbing down in between), or so I understand. Then given that glossy models tend to look more glossy compared to the real thing and putting two and two together to get five leads to the assumption that the varnish thickness is the key. (I think that is what is known as of the logical fallacy of confirming the antecedent.)

I suspect the reason has something to do with the scale and things like the smallness of radius of curvature of things like boilers and the viewer being able to change viewpoint almost instantaneously by the equivalent of many tens of metres and so see a whole raft of different specular reflections. In more practical terms, a gloss finish shows up every surface imperfection and paint nib as a glint, making the model look more like a toy.

There is one part of a model that I really do think looks best shiny and bright and that is real polished brass steam domes. My attempts at painting with brass-coloured paint looks lame.

A high gloss finish can make anything look like a toy!  ;D


The photo actually looks better than any I've seen on the road, perhaps because you can actually see reflections of things and not just a shiny golden blob whizzing past.

Then there is the opposite:


Perhaps because weathered models are quite common, it just looks like a really badly weathered model to me.

[Hobby]

With that second one I think the problem is that the rust is not where it should be if it formed naturally so it looks wrong... As you say someone has got out their weathering kit (brown spray can) and just done it at random without looking at real rust and where it forms.

[Stefan Krebs]

Of course, that reasoning regarding varnish thickness assumes you use the same varnish (and paints) on both, which would not be a good idea...

One aspect of any paint job are viscosity and surface tension, which you can't scale; the reason why real water on a model railway hardly ever looks realistic, especially, when flowing.

On the real deal you're not too worried about viscosity and surface tension, as long as you get an even finish. However, they are carefully designed parameters of any good quality paint! When it comes to corners and edges, they tend to be radiused to prevent injury, and where paints 'fill' corners and round edges, it normally doesn't matter. Scale that radius down and it becomes a sharp edge. but your paint will still 'fill' the corner and radius at the edge as the viscosity in combination with the surface tension 'pulls' around the edge.

The other aspect is that the 'glossiness' changes with viewing distance, i.e. the further the less gloss something looks. Mentally we compensate the effect as we're used to that, but this compensation is not scalable either, i.e. as we typically are much nearer to our models they appear too gloss, especially when surveying the realm!

By the bye, that golden car will be confiscated in most European countries as it is a danger to road traffic; other road users might get blinded by sun or light reflections in the paint job! That paint job makes it an MOT-failure in a lot of countries.



Cheers
Waldschrat

[B.Meldon]

I think regarding paint finish on models we should look to the way the ready to run manufactures do it.
They have the resources to have any finish on their locos and rolling stock they like, yet they go for a satin finish in almost every case.

It is just my oppinion but in 009 I think satin or matt finish always looks better than gloss on 009 models.

Brian Meldon

[Hobby]

But they don't cover up the sandpaper finish on some 3D prints half as well as a thick layer of gloss enamel put on with a wallpaper brush, Brian! ;)

[Stephen Rainsbury]

It is just my oppinion but in 009 I think satin or matt finish always looks better than gloss on 009 models.

Strangely enough I have just dug out some old plastic tank bodies left over from an old project (the turrets were use on a space station model) and was going to experiment with spraying them different colours and different finishes to see what looks best at that scale. 
I currently 4 cans of Varnish to try, 3 from Games workshop, and one B&Q brand satin, they are all good, but you can't put n more than two coats of a light dusting before you start to obscure details.
It doesn't help watching the two train series currently on TV and seeing the side of their locos shinier than a spiv's suit.
Stephen

[Stephen Rainsbury]

But they don't cover up the sandpaper finish on some 3D prints half as well as a thick layer of gloss enamel put on with a wallpaper brush, Brian! ;)

Which takes us back to the reason for the original post :-)

[Stefan Krebs]

Going back to basics, on the real thing you would use:
1.   A primer with corrosion protection on steel or similar, or an etch-primer on aluminium and galvanised steel. Paint doesn't stick well to zinc, that needs either weathering for 2 years at least, or an etch-primer. You can read that across to ZAMAK.
2.   Then you would use a filler in 1 to 5 layers to cover up blemishes, which would do nicely for those rough 3D-print surfaces; if it weren't for the fact it'll cover up any detail.
3.   For lushness of the colour you would apply a white top-coat now (except for black finishes) in 1 or 2 layers.
4.   Then it's time for the final colour, typically in at least 2 coats.
5.   To finish off you also may apply a clear coat or 5 to improve colour intensity.
Noting that today for top-class finishes you use a composite resin coat.

Problem is: you can't do that on a model, all detail would be lost, even without filler.
Conclusion: You can't match the colour of the real thing properly, somewhere along the way you have to compromise.

So yes, copying what we accept and like, i.e. from the manufacturers' is certainly the way to go. However, some of the paint layers listed above are there for a purpose, ignore that at your peril:
1. You need a primer to get the paint to properly stick to the surface, for most plastic materials, brass, copper and zinc-alloys an etch-primer is the weapon of choice. Make it a white or pale grey one to help with the lushness of the final colour.
2. You need your colour paint, obviously.
3. you may need now a high-gloss varnish for the decals to adhere well and become invisible after the last coat.
4. and you need your varnish to protect your decals and lining job.
As already discussed, semi-gloss or matt finish tends to look better than gloss, and thinner is the mantra.  ;D


Just the little bit I know about painting fences, cars, lorries, and boats.  ;) And no, I don't use Ronseal etc. for a reason.

Waldschrat

[B.Meldon]

I can only speak from my own experience, but I have never used any form of primer on the models I build.
I have always found that the paint works just fine provided the surface is de-greased.
I have used Humbrol and other makes of enamels, and in more recent years Tamiya acrylics as well, all applied with a brush. I also use Halfords satin black acrylic rattle cans.
These have been applied to plastics, tin, steel, brass and other materials, some on the same model and I have never had any problems with the paint not adhering to the surfaces.
That said the surface finish has to be made nice and smooth before painting.
I usually try and stay clear of 3d printed items as for me the surface finish is usually poor, requiring quite a lot of work before painting, far more so than with other materials.

I am not saying this is what everyone should do as other get good results using primer, it is just what I do.

[Hobby]

One major benefit with using a primer such as the ubiquitous Halfords Grey Car Primer is that it is very good at showing up any blemishes before applying the top coat.

[Stefan Krebs]

Dear Brian,

I've done that too, mostly in my younger days, and it works okay; 45 years hence I still have some models where the paint is okay. But the paint job isn't, as I wasn't experienced then. After doing my tour of duty in a garage with a truck-size paint workshop I now practically always use primer. I find it makes the top-coat spread more evenly, to say you get away with a thinner coat. If I skip the primer, as you do on a rush job, I can see its inferior finish.    ;D

Cheers
Waldschrat

[Stephen Rainsbury]

During my SciFi days I always used a primer, it somehow brings the model together and gives a good base to start from. I used White for figures, as it gave better skin tones, Grey for aircraft and vehicles, and Brown for natural scenes.
The only problem this time of year is that unless I pre-heat the garage sprays give a nasty mottled finish.

[Stefan Krebs]

Did I say 'paint-workshop', or didn't I?  ;) In winter everybody came into the paint workshop because it was nice (as in dust-free) and warm!   :D
Down in the pit under the trucks you froze not just the brass balls of the monkeys...

Of course, a bit of diurnal cycling during drying is one way to ruin a paint job.   :P

Merry Christmas
Waldschrat

[Stephen Rainsbury]

Did I say 'paint-workshop', or didn't I?  ;)

The point was duly noted, I was comparing the lives of us mere mortals to your absolute luxury  :laugh:
My 40 year old 2KW "Redring" fan heater does a Stirling job if you point it straight into my paint booth (large cardboard box) for 20 minutes before you start, and leave it on for 20 minutes after. So two coats with ten minutes between and that's and hour, which of course I can watch racking up the digits on our smart meter  :-[