Scratchbuilding pt.12: Two-Dimensional Curved Structures

Introduction

For a long time, I was put off the idea of airbrushing. The thought of having to control two things at the same time (both air, and paint flow) with one finger, the paint mixing, the difficult and/or time-consuming cleaning, the expense, and not least the huge choice of tools and the conflicting reports about them.

It all added up to something I just didn't want to try. In the end I was pushed into it by wanting to give a project a finish that wasn't available in aerosols - and it's been quite a positive experience.

 

Let's start with aspects I expected to be problems, but weren't:

 

Double Action Airbrushes

The requirement to meter both air (downward pressure) and paint flow (moving backwards) with one finger always put me off, but it shouldn't have done - you don't need to hit the same spot down & back each time for consistent results. Although the better airbrushes are capable of on-the-fly subtlety like that, you don't have to use it, as a lot of the setup is down to the air pressure the regulator is set at, e.g. 15 psi for fine, close-up stuff, up to 40 psi for greater coverage with an airbrush with a suitably sized nozzle (and not forgetting to move the nozzle further away from the work).

Using the control doesn't have to be two independent actions you need to think about separately, you can just move your finger in an arc - down to turn the air on, back to let the paint flow. At the end of the pass, forward to shut the paint off, up to shut the air off. 10 minutes or less ought to be enough to master the initial transition from rattle cans.

 

Paint Mixing

It's not difficult, it's just a question of finding what works for your paint. For Tamiya X- and XF-acrylic paints, the X-20A thinners (which is much better value in the 250ml containers) diluted at a ratio of two parts paint to one part of thinners works ok for a brand-new jar of paint, anything up to one to one - the consistency should be something like milk. Whether that’s full fat, semi-skimmed or skimmed is something experience will tell you. Buy suitable glass jars with lids, and/or keep the empty (and cleaned) Tamiya 10ml jars for mixing.

I've found it helpful sometimes to fill the inlet on the airbrush with thinners before attaching the paint bottle - that way there's something easy for the siphon action to start on before getting to the paint. Spray onto something other than the workpiece at first so you know that paint is coming through.

 

Cleaning

I'll admit my first time (when a double action airbrush seemed to completely dismantle itself) was a steep learning curve, but it gets a lot quicker and easier the more you do it.

For a typical double action, bottom (aka siphon) fed airbrush, an initial clean immediately post spraying could be:

  • remove the paint bottle. The inlet will drip paint, so be ready for that.
  • blow out any remaining paint, then immerse the end of airbrush in water (e.g., small goldfish bowl) & blow through. Remove from water & blow through again.
  • immerse in water again, put finger over end of airbrush while blowing through – this forces air (and water) backwards through the business end of the airbrush, carrying paint with it.
  • clean inside of inlet with cotton buds of similar.
  • blow through with appropriate thinners (either by attaching a spray jar full of it or push in with a small syringe) & until the spray comes out clean.

Elapsed time for the above is about a minute. This is enough of a clean when you're planning to use the airbrush again later for another coat of the same paint.

 

 Blowing through with waterBlowing through with water Pushing in thinnersPushing in thinners Almost thereAlmost there

 

For a different colour (or when you're done for the day) a more thorough clean is required, so in addition to the above:

  • Remove air cap, and nozzle holder (aka air cap body) & leave to soak in appropriate thinners.
  • Drip thinners into paint inlet & clean out with cotton buds or equivalent. Drip more thinners in & blow through, cleaning end of body. Repeat until clean.
  • Remove needle cover & loosen needle chuck. Making sure the trigger lever (and the rocker behind it) don't fall out, remove the needle & wipe carefully.'
  • Remove air cap & nozzle holder from thinners, blow through and/or wipe to check cleanliness. The outside face of the air cap needs more attention, use a cotton bud or similar. Screw back on to the body.'
  • Refit the needle carefully, set so it's just touching the nozzle, tighten needle chuck & refit needle cover.

With a little experience, this is a 5-minute job.

 

 Typical airbrush, partly dismantled for cleaningTypical airbrush, partly dismantled for cleaning Same airbrush, completely dismantled. You should rarely (if ever) have to go this far.Same airbrush, completely dismantled. You should rarely (if ever) have to go this far.

 

Cost

It doesn't have to be expensive - but the wide variety in equipment, prices, reviews, opinions, and so really doesn't help the beginner. Sensible advice at the time I bought mine suggested a cheap, Chinese made kit. Spending less than 70 GBP (which would be 100 GBP now?) on a small compressor with attached three litre tank & two airbrushes has worked out very well for me. If it hadn't, I don’t see why I couldn’t have sold it on for most of what I paid for it – so quite a cheap lesson if it turned out not to suit me.

 

After buying a few extras (such as a small goldfish bowl, quick release adaptors, a fancier air hose, lots and lots of bottles, more cheap airbrushes (single action external mix, more DA siphon airbrushes, DA gravity fed), a small extractor cabinet, plus a nice wooden box to keep the smaller bits in – including no end of 22ml glass jars) I had a setup capable of quite varied work.

 

Now, after 4-5 years of doing 2-3 "big" projects a year, I felt I'd could _possibly_ use something of higher quality in the airbrush department. Adding a zero to the cost of beginner tools buys you only “entry level” at the quality end of the market, so it’s not something I’ve done yet.

Something I have done recently is buy – but not try - a cheap mini HVLP (high volume, low pressure) spray gun with a 125ml cup & 0.8mm nozzle (plus coiled hose & adaptors) to try to get greater coverage for base colours.

I also have a “big” compressor (c. 2hp with a 24-litre tank) to which I’ve added an adaptor/moisture trap/regulator assembly. This comes in handy for bigger areas with an airbrush with a larger nozzle, but it will be barely adequate for the HVLP gun.

 

A basic airbrush setup, almost ready to spray – and clean up afterwardsA basic airbrush setup, almost ready to spray – and clean up afterwards

 

I’d also add eye protection & a mask to the above pictured setup. A mask like a 3M 4251 seems expensive compared to the throwaway options but is very effective and will last a long time in hobby level use.

 

Nomenclature

Let's a have a quick look at some of the terms you'll see applied to airbrushes:

  • Double Action (or Dual Action, DA): the trigger controls airflow (pushing down) and paint (pulling back). Generally considered superior to Single Action, where your pointy finger controls only the air.
  • Bottom Fed (aka Siphon or Suction Fed): paint is drawn up from the cup or jar fixed under the airbrush and relies on air leaving the end of the airbrush to form a slight vacuum.
  • Gravity Fed (aka Top Fed) airbrushes have paint cup fitted on the top and are considered to be capable of finer work. I’ve found mine especially useful for quick mixing & spraying of small quantities of paint.
  • Side Fed models give you the option of rotating the paint cup to any angle so it can be upright no matter what angle you use the airbrush at. Some models also give the option of a bottle, turning it into a siphon fed airbrush. However, this flexibility comes at the cost of longer clean up.
  • Internal Mix: paint & air mix within the body of the airbrush (though sometimes only barely within) resulting in a finer spray than an External Mix airbrush, which can be better at covering larger areas.

These terms combine in several ways to describe an airbrush. For example, I have several are bottom fed airbrushes, some are double action, internal mix, others are single action, external mix.

 

Moving on, Needle/Nozzle Size is an indication of the sort of work you can expect an airbrush to be best for. A small size is going to be great for fine work such as 1:35 scale armour camouflage but is going to struggle with slab-sided 1:10 scale builds.

Sizes seem to run from a nominal 0.15mm up to 0.8mm, an "in between" figure, such as 0.35mm is not going to excel at either (although much can be achieved with varying the air pressure) but can be used for a wide variety of tasks.

 

Thread Sizes can be minefield & really makes a case for buying a kit, or at least sticking with one manufacturer. Half the problem is that any measurement you're likely to take often doesn't translate into the elderly standards the fittings are known as. So far, I've come across:

  • 1/8" BSP. BSP means a “British Standard Pipe” size - which refers to the bore of the pipe, not the diameter of the thread, or pitch. I’ve found this on the majority of the airbrush equipment I've bought. Note that this thread – also known as 8V1-32, or 0.305"/0.307", or 7.7mm - and 32tpi – looks very similar to the nominally 8mm Schrader valves which are the most common type found on cars, motorbikes & bicycles, but is completely incompatible.
  • 5mm. I’ve found this on copies of the Badger 350 (I guess the original has it too?).
  • 1/4" BSP. Found on some larger compressors & the equipment you'd normally run off them, such as media blasting cabinets - but also one end of some adaptors.

Adaptors to switch between the various standards are widely available, but it's an added layer of complexity.

 

Good Reasons to Use an Airbrush

Better results than brush painting. The TPz Fuchs in the pic below is not the greatest example of this, featuring as it does my first attempt at airbrushed camouflage - but consider the base colour: at 1:72 scale any brush strokes would have been positively enormous.

Softer/better edges on camouflage paint: brushing or masking for aerosols gives unconvincing hard edges, stand-off masking with aerosols is a bit unpredictable - even more so for smaller scales. I've already given my excuses for this vehicle - but think how much worse it would have been with hard edges to the different colours.

 

1:72 TPz Fuchs1:72 TPz Fuchs

 

Custom Colours. Consider the Sand Scorcher below - this Tamiya Sky Blue is only available in a jar (X-14), without an airbrush the options would have to brush paint or use a different colour. That's not so important but following on from that is the ability to mix any colour you like and apply it in way that gives good looking results.

See the (work in progress) NSU TT body below, for example – it’s a mix of Tamiya PC White, Green, Blue & Black (and X-20A thinners) for a dusky baby blue result - not a colour you’d find in a PS- aerosol.

 

Sky Blue Sand ScorcherSky Blue Sand Scorcher NSU TT bodyNSU TT body

 

Paint Effects. Bleached/faded paint (as if it's been out in the sun or rain for decades) starts with a matt or satin finish - achieved by adding Flat base to your colour of choice, or Flat Clear over it.

A bleached look comes from adding white, initially I was a bit timid at this, mixing up many different shades to ensure a good transition (see the scratch built Unimog tanker below) but got more confident & used fewer variations as time went on (see the Laplander, also below). For the open top Scorcher, IIRC I used one halfway 50/50 blue/white tone, and then moved on to straight white.

The series 3 Landy was a custom mixed blue, then white without any intervening steps.

 

Faded/Bleached scratch built Unimog TankerFaded/Bleached scratch built Unimog TankerFaded/Bleached Volvo LaplanderFaded/Bleached Volvo Laplander

 

Custom Sand ScorcherCustom Sand ScorcherScratch built Land RoverScratch built Land Rover

Lower Cost …? It would be quite easy to demonstrate that a 100 GBP airbrush setup + 25 10ml glass jars of paint at 2GBP each costs the same as 25 aerosols at 5 GBP each, and that it becomes cheaper still as the higher the number of shades go up, so it _can_ be cheaper if you plan to spray a small amount of a large number of colours.

Pots of airbrush and polycarbonate suitable paints though can cost as much as aerosols though, and are much less widely available – meaning you’re going to have to figure in postage costs too.

I don’t think you can use comparisons of the various costs to justify buying airbrushes - but them being better value is a whole different argument.

 

Rescuing dying/dead aerosols. Rattle cans – especially once started – can lose pressure just sitting on the shelf.

If you know the correct thinner to use (and that can be a bit of a trick) you could decant the paint from a can that’s lost far too much pressure to want to use, then thin it & spray through an airbrush.

 

Better storage options? There are lots of hobby sized paint racks from small scale producers on Etsy & the like, some of which can fit in and around your current hobby space. For the truly dedicated, you could probably find a rack from a defunct (or hopefully just refitting) model shop or motor factor, but more likely you’ll find yourself sorting through a plastic crate or two.

 

Better for the environment? “Water Based” airbrush paints – and especially their thinners, reducers / cleaners / whatever – still have solvents in them, and I’m not aware of any studies comparing the environmental damage of either option.

However, I know I’m quite happy to airbrush things indoors with proper precautions, knowing that the stink & dust is unlikely to cause anyone to get ill – whereas I’d never use aerosol paints indoors.

 

Conclusion

I don’t think I really need to say much more than “go for it, and good luck” :D

With the exceptions of buying yourself the correct JIS points screwdrivers for Tamiya RC kits, and the small number of tools and supplies to start building your own accessories and bodies in styrene, a cheap airbrush/compressor setup provides the most “bang for the buck” of anything you could get to expand your traditional RC/model making horizons.

I put the “traditional” caveat in there, as learning to use a free CAD package – and therefore opening up the realm of getting your own parts 3D printed – has the word “free” right there.

 

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Written by TB member Jonny Retro