Skin Deep – Pt.1

Skin Deep – Pt.1

Available in a whole range of colours, Solarfilm is easy to apply once you’ve mastered a few basics.

Over the last 30 years, Solarfilm has revolutionised the way in which we cover our models, making it possible to achieve light, durable and spectacularly colourful finishes. Unfortunately, like everything that involves a certain dexterity (and attention to instructions!), its equally possible to create some spectacular disasters! Not everyone, it seems, has discovered the secrets of a perfect Solarfilm skin, and this article is intended to help such troubled souls and iron out their models wrinkles and folds.

Well look at actually applying the film later but for the moment, lets talk about preparing the airframe and the tools you’ll need.

NO SHORT CUTS

First of all, lets be quite clear: no matter how shiny the Solarfilm is when you start, the quality of the finish you achieve will only be as good as your preparation. If there are gaps in your wooden airframe or if its improperly sanded, you won’t be able to hide these defects with the film. The only way to a perfect finish is through careful building followed by a lot of elbow grease as you sand, fill and sand again until everything blends together perfectly. There are no short-cuts, I’m afraid.

SOLID FOUNDATIONS

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When constructing the airframe, then, take great care to join all the parts as accurately as possible without forming steps and so that the minimum amount of glue is required to make the joints. If mismatches between components do occur, sand the step down to match the level of the main component, using scrap balsa if necessary to bridge the levels and give yourself something to work with. You’ll find the whole sanding process much more enjoyable and a good surface finish much easier to achieve if you’re working on neatly assembled woodwork.

When making block areas with compound curves, such as wing tips or nose blocks, or if you’re shaping sheet material, pay close attention to your marking out at the pre-carving stage, and ensure that your profiles are accurate. When you start carving, use a razor plane with a very sharp blade, and carve carefully until the material is shaped to within about 1/16 of its finished size. That’s the time to stop carving and get out the 180-grit paper and sanding block.

Sand your block or sheet component to match the main airframe, then continue to blend everything together until you’ve achieved what I call an overall rough smoothness. In this condition the wood will be generally smooth with only minor constructional inaccuracies still to be rectified.
 

SAND, AND SAND AGAIN
Remove nicks and dings by moistening the damaged area with water to make it swell, then sand when dry; apply filler to any small holes or cracks and rub down. To give the whole assembly an even finish, wipe the airframe with a damp cloth to raise the grain, and then cut it back with your (now very tired) 180-grit paper.

The next stage involves using 300-grit paper to create a really smooth finish. Be careful with these finer papers, though, as they can clog easily and damage the timber – you need to judge carefully how much pressures required to get the paper to cut the surface of the wood without actually scoring it.

When you’re satisfied with the finish, clean the dust off the airframe and start again with 400-grit paper. You can work freehand now as all you’re really doing at this stage is to polish the airframe. Again, watch out for clogging: tap the paper frequently to keep it clear, and scrape any caked dust from the paper with the edge of a scalpel blade.

Airframe preparation is essential.
I tend to carry on this polishing process as far as 1200-grit paper before applying Solarfilm, but generally speaking that’s not necessary. Most woods give a perfectly satisfactory finish with just medium-grit paper, and its only the hairy sort of timber that takes a lot of work with fine-grit papers to get really smooth.

When you’ve finished sanding, clean down the airframe thoroughly as every speck of dust will show through the film and spoil the finish. I find that a medium-size domestic paintbrush shifts most of the debris, leaving me to give the airframe a final wipe over with a tack-rag just before covering. If you like, you can suck the dust away using a vacuum cleaner fitted with the small circular brush, but be careful that you don’t score the timber with the bristles.
 

A CLEAN CUT
Before you can cover your model, of course, you’ll have to cut your film to shape. Solarfilm can be worked with a scalpel, a Stanley knife or scissors, providing they’re sharp. Alternatively, you can use Top Flite’s very clever Smart Cut tool, that takes a pair of no.11 scalpel blades which are clamped in place to give an edge overlap of either 1/16 or 1/8. This helps with all manner of trimming tasks.

When cutting Solarfilm, a long metal straight-edge will often come in handy. I use either a long steel rule or a piece of extruded aluminium window frame, depending on the length of panel required.

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Curves, meanwhile, are easy to cut freehand with a blade or scissors.

HOT SOURCES

To attach the panels to the airframe and shrink the film to shape, you’re going to need some sources of heat. While you can get away with using a domestic iron and a hair-dryer for tacking and shrinking film, its well worth investing in one of the specialist tacking irons and heat guns: purpose-built irons are easier to handle, while heat guns pack more punch than a hair-dryer.

Whatever type of iron you use, you’ll need to make sure that you keep the sole clean. Specialist irons have non-stick coatings, but can still collect a build-up of Solarfilm pigment; remove it when the irons cold using meths or cellulose thinners. If you’re using an ordinary household iron, you may need to remove hardened debris with fine emery paper followed by a wipe over with meths or thinners.

Tools of the trade

It’s also worth getting yourself a narrow-tip heat-sealing tool such as that offered by Protech. These devices come with a pair of specially-shaped bits that are absolutely invaluable when you’re sticking film into confined corners. Of course, you can also do this sort of fiddly work with a no.18 scalpel blade heated on the sole of an iron. The only trouble is that the blade doesn’t stay warm for long, which can lead to problems with adhesion as Solarfilm really depends on maintaining the correct iron temperature.

WORKING TEMPERATURES

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The adhesive backing of Solarfilm will stick to wood and to other films at 90°C; the film itself shrinks tight at 100°C, and really pulls tight at around 110°C. This being the case, in order to establish accurate working temperatures, you’ll find it useful to buy a Coverite thermometer, which you’ll find in all good model shops. The thermometer is placed on the sole of the iron and a simple expanding spring mechanism shows the temperature. Mark the established low, medium and high temperature settings on your irons thermostat dial so that you can make adjustments quickly and precisely in future. Don’t forget to allow a couple of minutes for each temperature change to take effect, though.

A more pragmatic approach to judging iron temperatures is to simply place scraps of Solarfilm on the sole of the iron: a very slow dimpling of the film indicates 90°C; a more pronounced puckering of the film says 100°C; and a rapid shrivelling means that the irons at 110° or more. Remember, it’s always better to start with an iron that’s too cool and gradually increase the heat; if the irons too hot initially, you’ll start burning holes in your film!

Talking of checks, its not a bad idea to ensure that the films adhesive backing is doing its job. In this respect, try ironing some test strips onto scrap balsa at the recommended tacking temperature. When you peel the strips off again, the adhesive should bring an ultra-thin dusty-looking layer of wood with it – clear proof that all is well!

A purpose-made glove like this protects the hands
PRESSING MATTERS

Once you’ve actually covered the model and shrunk the film to shape, its necessary to press the Solarfilm into contact with the whole airframe. You can do this with a wad of soft paper tissue or a soft cloth.For some reason, though, I’ve always found that tissue leaves a haze over Solarfilm, while a rough cloth can score the underlying balsa.

Top Flite’s Hot Glove, on the other hand (no pun intended), looks and works just like an oven glove. It protects your hand from the blast of the heat gun, while applying a gentle, even pressure on the film.
It’s no secret that every modelling job is made easier by the right tools, thorough preparation, and a little forward planning – the rest of it comes down to experience and technique. Covering your model with Solarfilm is no exception, so, having collected our hardware and readied the airframe last time we met, well skip the pleasantries and get straight down to the planning and practice, shall we?

A superior finish like this is what you’re aiming for.

WORK METHODICALLY
Aim to begin by dealing with any parts of the airframe that can be covered before they’re fitted to the model, such as balsa-block fin base fairings. Next, tackle all the awkward corners of the airframe, like control surface edges, followed by built-in items – wing fillets, for example – which are best covered using 1/2 strips of film. You’ll also need the narrow tip of that sealing iron you’ve just bought, or at least a heated blade, to make a neat job of areas such as non-filleted tailplane-to-fuselage joints. The trick here is to attach the film to the bottom of the fin, pull it well into the angle between the fin and horizontal surface, then tack it gently along the very base of the fin to hold it in place. This will stop the film pulling out of the corner when you attach it to the horizontal surface, and give you a crisp, clean angle between the tailplanes.

Where you have to cover concave fuselage-to-wing fairings, you’ll find that fitting the curved hot shoe to the narrow-tip sealing iron is the best way to persuade the film to stay in place. Control surfaces, meanwhile, are relatively easy to cover using strips of film on the side faces and along the leading edge; an ordinary modellers iron is fine for sealing the edges.

Once all this fiddly works out of the way, you can turn your attention to the main airframe panels.

Ok, that’s it for now. In part.2 tomorrow, we’ll start covering! 

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