Choosing a kit to suit your modelling ability

Model kit contents sometimes cross-over by containing more than one medium, but on the whole you'll be able to identify the various types by the following descriptions...

 

Injection Moulded

These are probably the most common type of model kit, with tanks, cars, aircraft and ships being popular subjects. Usually produced in a hard polystyrene plastic which can be joined by a number of glues, the nature of these kits is such that they are built from components which have to be sub-assembled before final assembly and complexity can range from a few easy to assemble parts to containing dozens of components requiring expert modelling knowledge.

Most injection moulded kit components align together using a system of locating pins and holes or slots and tabs. Accuracy of these often determines whether the kit’s a good one or not, but badly located parts don’t always mean disaster, as corrections by the model maker can often be made. Components are generally identified by a series of numbers or letters, or both, and instruction sheets, leaflets or booklets provide written or diagrammatic instructions of the assembly sequence. Instructions vary enormously in their quality and can cause problems for the novice, although a trial assembly of parts without the use of glue will often answer queries that are not clear.

Producing injection mouldings unfortunately involves a very expensive series of processes, meaning only large manufacturers produce the vast majority of this type of kit. Much of the cost is generated by the tools required to mould a kits components. Basically, molten plastic is injected under pressure into a tool made from steel. This tool, which will normally be constructed from several pieces, holds the shape of the components. The manufacturing process, and the cost of tooling, is why injection moulded kits are supplied as a series of components on a framework, known as the sprue. This enables far more components to be produced from one tool, helping to reduce some of the costs. Whilst this saves money, it also means that each component has a runner or feeder joining it to the sprue. These indicate where plastic is fed to the components, and whilst a necessary part of the process, they have caused problems for modellers in the past. Size and positioning of runners is critical; too big and they make it difficult to remove components from the sprue, too small and components can become misshapen due to a lack of plastic getting to the tool. Other problems with the process include flash, sink marks, distortion, and parts that don't match up very well. These are often caused by poor tooling, which comes back down to costs. It's a case of the more money spent on tooling, the better the quality of the kit. Manufacturers either have to sell more kits, or increase prices to recover costs. It's a vicious circle that can sometimes prove frustrating for modellers.

All of these generalisations regarding the construction and manufacture of injection moulded kits are due to there being no set standards adopted by the manufacturers. Some provide location pins and some don’t, some provide instructions with diagrams and some are just written, so you can see that the modeller has to build up knowledge over the years. A main advantage with injection moulded kits however is the price, for despite the expensive tooling process, the number of kits able to be produced means that retail costs are on average around twenty pounds, but can vary from as little as three pounds to as much as one hundred pounds or more, depending on the type and it's complexity. Another advantage is their availability, because they are very often available from general hobby shops, toy shops and toy departments as well as model shops.

 

Vac Formed

Unlike injection moulded kits, the components for this type of kit are cut from a sheet of material which are then cleaned prior to assembly. The tabs or pins that are used to locate injection moulded parts are absent on vac formed kits, and so these have to be added from scrap plastic.

The vac formed kit is not really suited to the novice, but construction skills are reasonably basic, and as such can be acquired fairly quickly by modellers new to the medium. Prices can vary depending on the production run and the complexity of the kit. Basic vac formed mouldings are often supplemented by white metal castings and sometimes, injection moulded plastic components. Their inclusion can result in slightly higher pricing, due mainly to the costs involved in producing these additional items, but on the whole they are similar to those of injection moulded kits.

The great thing about vac formed kits is the low costs involved due to a relatively simple production process. Basically, the production of vac formed kits is a matter of heating a sheet of thin plastic which is then either drawn down onto a tool, or pushed into by the tool. The plastic then takes the general form of the tool, but by applying vacuum suction to the plastic via tiny drilled holes in the tool, the sheet is pulled down over it to capture all of the detail. The process can be very successful, but there are limitations. The level of skill the tool maker or the person operating the vac forming machine has determines how good the results are. Problems stem from the thickness of plastic being used, and if the tool is made incorrectly or the moulding isn’t pulled properly, it is possible for the mouldings to have large radii in the corners, or lack sharp detail. Other problems can occur, but skilful tool makers and machine operators can usually work around them. One way to overcome large radii on the mouldings, is to produce a female tool rather than a male tool. A male tool reproduces the shape of the model but with the plastic thickness removed from all surfaces, so that when the plastic is pulled down over the tool, the resulting mouldings are dimensionally correct. A female tool is the reverse of this, with the plastic being pulled into a hollow tool. This has the advantage of putting the sharp detail on the outside of the mouldings, but producing the tool is a little harder. The tool is also produced to the dimensions of the finished component; no allowance for material thickness is needed.

This type of kit is readily available from a number of manufacturers and, because of the relatively low cost involved in producing this type of kit, the process is open to 'cottage industry' manufacturers. Production runs can be low, and there are many established moulding companies that are able to accept vac forming jobs from small manufacturers, thus reducing the need to invest in expensive machinery, and therefore reducing overheads. It’s often these smaller manufacturers that are able to produce kits of the more unusual subjects, subjects that larger manufacturers wouldn’t normally consider due to the relatively low interest and subsequent potential sales.

 

Resin

These kits often consist of very few components which are usually easy to clean and can be glued with conventional plastic glue; they require either super glue or an epoxy adhesive, both of which are simple to use.

Resin kits are, in my opinion, far simpler to construct compared to injection moulded kits. The manufacturing process involved in the making of resin kits usually means that there is a little less construction work needed. Items that would be built up from a number of components in an injection moulded kit can often be cast as a single piece in resin. The resulting components often require just the moulding 'plug' to be cleaned up before assembly, the ‘plug’ being the additional resin that is left at the point where the resin is poured into the mould. Again, they are quite different to injection moulded kits, requiring slightly different skills. Resin components are cast in one of a variety of polyurethane resins that are available from a number of manufacturers. A rubber mould is constructed of the component into which the resin is poured; this can be a single or multi-piece mould that is taken from a master model of the component. Once the resin has cured (set), the component can be removed from the mould and more resin added to make another component. The relatively simple manufacturing process lends itself, in the same way as the vac formed kits, to the ‘cottage industry’ manufacturer, and some of these have perfected the process to such an extent that the models produced are of a much higher quality than some other materials. However the process does have limitations, and there are ways in which the process can be used badly, yielding poor results. Due to the costs of the resin and the moulds, plus the relatively low production runs involved with resin kits, the prices of these kits often tend to be a little more expensive than injection moulded kits.

 

White Metal

Apart from the obvious weight difference, the main difference between a resin and a white metal kit is the casting; metal is cast when hot whilst resin is cast when cold. As such the types of moulds used are slightly different, being capable of withstanding the high temperature of the molten metal.

White metal is not only used for kits and miniatures, but for accessories in other kits too, such as vac formed, resin, and vinyl. They aren’t as common as some of the other types of kit mentioned above, but there are a large number of kits that use white metal in them. When cast correctly the detail that one can expect from a white metal component is second to none, and as with resin components, these can be cast in sizes that would normally be built up from several pieces in an injection moulded kit.

When cast properly, white metal kits only require a little work before assembly, removing the runners and cleaning up any flaws that are present on the castings. The tools used are in general the same as those used on any other kit, including sandpaper, files, knives and filler. White metal kits can be fixed together in a number of ways. The easiest way for the beginner is probably super glue, which gives an instant bond, and does not require any additional clamping whilst the glue sets. Two-part epoxy glue can also be used, but this does mean that there are occasions when components will need to be held in place whilst the glue sets. The final method of fixing components, and not really recommended for the inexperienced, is soldering, where the components are soldered together. This requires a little more skill, and a low temperature solder is best used, otherwise there can be occasions when the heat of the soldering iron will melt the white metal components!

Vinyl

Different to the type of kits you’re probably more used to building, vinyl kits usually consist of just a few components and are very simple to put together. In fact, they’re one of the simplest forms of model you can build, and detailing quality is superb on most available kits.

Construction once again requires the same basic tools that you might use for other types of models and the components can be glued together using super glue. The majority of problems that people encounter when building vinyl kits come from painting, but with correct preparation and paints, excellent results can be achieved.

Vinyl kits are manufactured by a simple process that effectively blows vinyl into a female mould that has been made to the shape of the components. The vinyl conforms to the shape of the mould, and when removed, the exterior of the vinyl moulding reproduces the shape of the inside of the mould exactly, leaving just a small amount of excess to be removed. This process allows very complex shapes to be reproduced in single pieces rather than a number of components that then have to be glued together.

In recent years, vinyl kits have become a lot more common and have, to an extent, stepped in on kits that would have previously been produced by vac form. As with vac formed kits, vinyl tends to cover more specialised subjects, bringing modellers kits that would not normally be injection moulded. However, one problem that still remains with these kits is the price, which tends to be quite high, discouraging some modellers from trying them out. If you can afford to try out one of these kits, it’s well worth the experience.