Building Vacform Models Part One - The Basics. By Brett Green

Building Vacform Models

Part One - The Basics

by Brett T. Green

Meteor F.8
Aeroclub Vacform 1/48 Kit

See also "Gloster Meteor F.8", a Construction Feature on HyperScale, for a detailed description of a vacform modelling project.

Introduction

Why Build a Vacform Model?

Modellers today are presented with a breathtaking choice of kits. Most major aircraft, armour and car subjects are already available in injection moulded form. Very little effort is required to build a great looking model.

However, the peculiar nature of many modellers is that we often want to build a very specific subject. Sometimes we want to build something because it is not available in mass-produced form. Others may simply wish to rise to a new challenge.

Technological advances have not been limited to the injection-moulded model industry. Vacform models have made stupendous leaps in quality and detail in the last ten years. Vacformed parts now feature surface detail to rival the major manufacturers. Many vacform kits are now multi-media masterpieces with brass etched parts, white metal and resin adorning the basic plastic.

And if you want to build a Barracuda, a Firefly, a Hudson or a Caribou in 1/48 scale; or a Boomerang in 1/32 scale; there is only one game in town – vacform!

What is Vacform?

Vacuum Forming (vacform) is an inexpensive method of producing basic shapes on sheet plastic.

A master pattern is first built by a pattern maker. A female mould is then created from the master, Finally, heat and suction is applied to flat sheet plastic to produce a raised impression of this female mould. The limitations of this method mean that it is not possible to replicate undercuts and some complex shapes.

The modeller is left with the task of cutting the parts off the sheet and cleaning them up for assembly.

The big benefit of vacforming is that big tooling costs are avoided, making it practical to produce a short run of esoteric subject matter that would not otherwise be available.

What Vacform Model Should I Start On?

I recommend a conversion for a first attempt at vacform modelling.

Falcon produce a number of “Triple Conversion Sets” including Spitfires, Bf 109s and a number of Century Series jets. Sierra Scale Models also produce a very high quality Wirraway conversion.

These conversions contain a small number of parts (usually two fuselage halves, a canopy and some details) making them an ideal introduction to this media. The Falcon and Sierra conversions are still in production.

If you really want to tackle a full kit, then select your first model from the list of “High Tech / High Quality” manufacturers below.

Hi Tech/High Quality?

The finished product from any of the following manufacturers will match the standard of many injection-moulded kits. These companies usually supply smaller detail parts in injection-moulded plastic, resin or white metal. The modeller is not required to fabricate many (or any) detail parts. Instructions and decals are typically included.

The following list of manufacturers is not comprehensive, but is a starting point:

Dynavector

PP Aeroparts

Sierra Scale Models

Aeroclub

Falcon (later releases)

Karo As

MPM

Koster

Aircraft in Miniature (1/72 Scale Civil Subjects)

FM (Australian company – 1/32 scale Boomerang)

OzMods (Australian company - 1/48 scale Caribou)

"DIY" Kits

There is another category of kits that should not be attempted by the beginner.

They are typified by companies like ID Models. The modeller is presented with nothing but a few sheets of vacform plastic. Features such as landing gear and cockpits must often be built from scratch. Surface detail may be soft, or missing altogether. And decals? What are they!

Although these kits are not for the feint hearted, they do fill a niche for modellers who have very specific interests. Despite their very basic nature, they are better than nothing. However, the modeller should have experience of vacform modelling and scratchbuilding before commencing this style of project.

Building a Vacform Kit - The Basics

The Tools

As with any modelling project, an appropriate set of tools is essential.

The biggest difference between vacform modelling and building a conventional injection-moulded kit is the preparation of the parts. Specific tools required for parts preparation are available inexpensively from the local Supermarket or Hobby Shop.

Here is my suggested checklist of tools for dealing with vacform parts:

Tool	Purpose
Hobby Knife with Several New Blades	General cutting and cleanup.
Hobby Knife with Several New Blades	General cutting and cleanup.
Scriber	My preference is an Olfa P-Cutter (also available as a Tamiya Scriber). This tool is an alternative to a knife for removing large vacform parts from the sheet. It may also be used to restore or improve surface detail on plastic parts.
30cm Steel Rule	Essential for measuring and cutting straight edges.
Pencil or Black Marker	For marking edges and part descriptions
Scissors	A sharp, strong pair of scissors. Handy for cutting excess from plastic sheets
Side Cutters	For “nibbling” around small vacform parts before final cleanup.
Pin Vice	With drill bits for drilling locating holes.
Emery Boards	Disposable nail files. I find these cheap files indispensable.
Nail Buffing Stick	For final polish.
Glasspaper	Various grades of paper from around 400 grit to 2000 grit
Sanding Block	Either a small block of wood, or a reusable sanding block such as the Sandvik “Handy Sander”.
Liquid Glue	For a strong bond between vacform parts with no locating pins.
Super Glue	To bond small metal or resin detail parts (super glue should not be used for parts under load).
Epoxy Glue	To secure multi-media parts under load (eg undercarriage)
Tape	I use various widths of Tamiya masking tape for many tasks including test fitting and securing parts while glue dries.
Two-Part Epoxy Putty	My preference is Milliput White. The grain is very fine, it stays workable for at least 30 minutes and it is easy to shape on the model. Doesn’t smell either.
Surface Putty	Mr Surfacer or similar will ensure a smooth, blemish-free finish.
Putty Trowels	Nothing fancy – I use a staple remover (my favourite), old knife blades and ice-cream sticks.
Tweezers, Pliers and Clamps	For handling and holding small items.

Getting Started

It is important to follow recommended assembly sequence and instructions in this style of kit. If instructions are supplied, read them! Familiarise yourself with the instructions and identify all the parts before you start.

Preparing the Parts

I follow a set sequence when preparing vacform parts:

1. Draw Around Parts – Take your marker or pencil and draw around the outline of all the parts, making sure that you get into the edge where the part meets the sheet. Don’t worry if the line is thick.
*2. Scribe Around Parts* – Now take the scriber and score, lightly at first, all around the parts. Hold the scriber at 45° angle to the part (see picture). Don’t leave a border – scribe right up against the part. Repeat the scoring until the scriber has nearly cut through.
*3. Remove Parts From Sheet* – Use your scissors to cut a section of the backing sheet around the part away from the main sheet. Next cut some “channels” into the backing sheet toward the part. You’ll need more “channels” on curved parts. Now simply snap off the backing sheet from the part.
*4. Clean Up The Part* – You will be left with a part that has a black line around its edge (that you marked earlier), and a thin wedge of plastic below the line. The black line indicates the limit of sanding. Don’t sand above this line! Use a sanding block or a large, coarse nail file to sand off the excess and check your work regularly. Keep the sanding block wet while working – it’ll make it easier to clean up later.
*5. Thin Trailing Edges* – Generally, trailing edges will need more attention even after the excess plastic has been removed by sanding. I find that sanding trailing edges is tedious and inefficient. Try using the back of a hobby knife blade to scrape the inside surfaces of trailing edges to achieve scale thickness.

Getting Ready to Assemble

Vacform parts don’t have any locating pins so extra care must be taken to ensure correct alignment.

Tape major assemblies together to find any problem areas, then work out a plan to deal with them.

It is sometimes helpful to add small rectangles of scrap plastic sheet as locating tabs for parts with a fairly straight, flat join (eg fuselage halves and engine nacelles)

Thermoforming

Thermoforming allows small parts to be custom-made. No special equipment is required. This method is useful for creating replacement canopies of small, simple shapes. Follow these steps:

1. Master - A simple master can be made from plastic, balsa or metal.

2. Frame - A frame should be made up with a hole big enough for the part.

3. Preparing for Thermoforming - A sheet of white styrene or clear acetate should be secured to the frame. I usually tape the plastic to the outside edges of the frame. Use fairly thick plastic as this method stretches (and therefore thins) the produced part.

4. Taking the Plunge – Hold plastic in the frame over a candle until the plastic softens. Don’t hold it too close and make sure you have a bucket of water in case the plastic catches fire! When the plastic is soft, plunge the master into the plastic and through the frame. Immediately remove the plastic from the heat source. You may even wish to dunk the part in water at this point.

5. Do It Again – This is a trial and error method. You probably fouled up the first time! Try again until you are happy with your replacement part.

Filing and Sanding

Vacform modelling usually leaves more gaps and joins than a corresponding injection kit. My method of filling and sanding a vacform is as follows:

1. Main Filling – I like Milliput for a number of reasons. As a two-part epoxy putty it adds structural strength to the model. It isn’t just sitting between a gap. It is also very pliable and stays that way for a long time. The grain is extremely fine and it is also easy to sand, wet or dry. The key to using Milliput is in the mixing. I never mix pieces that are bigger than half the size of a pea. This allows me to rub the two parts briskly between my palms until it is a thin snake of putty, then roll it up into a ball and repeat several times. The warmth of the friction improves the pliability too. Apply the thoroughly mixed putty to gaps, and shape with a wet finger or a putty trowel.

2. Sanding – When the Milliput is dry, start lightly sanding with 600 grit paper. Don’t go too heavy – vac-form material is softer than injection moulded plastic and it scars easily. Use progressively finer grades until a smooth finish is achieved

3. Finishing – The main disadvantage of using Milliput on vacforms is that the putty is white and the plastic is also usually white. This makes it difficult to ensure that all the tiny gaps are filled. I therefore brush on a coat of “Mr Surfacer 1000”, followed by a light sanding. This helps achieve a perfect finish.

Conclusion

Building a vacform model can be rewarding because it introduces new skills and can open doors to a range of otherwise unavailable subjects.

Don’t be afraid to stretch yourself and test some of these new techniques – you never know where it might lead!

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