Working With Resin Components

THERE ARE A NUMBER of manufacturers using resin castings for major body components, and while there are still modellers who prefer an allmetal approach, there is little doubt that a quality casting (which is of course only as good as the pattern from which it was made) will save a considerable amount of time. This is particularly true where there are complex shapes involved, whether it is a Stanier firebox, a Bulleid ‘airsmoothed’ casing or a diesel cab.

The following notes assume a starting point of a large structural casting, not a small item of detail.

The resin castings should be first washed in warm water with a mild soap/washing-up liquid, and then rinsed well. The castings should require very little finishing, principally the removal of mould part lines, and in making sure flat surfaces are truly flat. Any surface imperfections are best wet sanded, ideally using fine-grade wet and dry paper. Fibreglass burnishing brushes may also be used, though resin dust should not be inhaled and hands should be washed after work.

A well-designed casting should make provision for being attached to flat surfaces, for example a footplate or cab, by having areas that will take self-tapping screws, with drilling points (drill 1/16 inch) marked on the casting and corresponding holes in the etches or other castings. Typically the self-tapping screws are No.2 (2.2mm) x ¼ inch (6.5mm) Pozi self-tapping pan head. This has the advantage that components can be separated for painting. You do have to be careful not to overtighten the screw, or in breaking down the components too often to avoid stripping the thread. It is always better to have a mechanical fixing if possible, rather than just relying on a glued join.

Where the kit has resin to resin panels, there is normally a flange on one of the components. Here the panels are usually glued together with a ‘superglue’ or cyanoacrylate adhesive. The resultant join is quick to make and strong, so it is important to get it right first time. A couple of spots of glue are used to tack the pieces in the right position, and then a medium viscosity glue is fed into the join when you are satisfied all is well.

Roket Max (thick, sets 10-20 seconds), Rapid (medium, sets 5-10 seconds) and Hot (thin, sets 1- 5 secs) are all useful in handling such joints.

Bonding parts to the resin casting is best done with epoxy resin two-part adhesives such as Araldite Rapid or one of the cyanoacrylates. Where there is a spigot on a casting or machined part that is attached into drilled holes in the resin, an adhesive such as Loctite 480 is ideal. It is toughened and has a slightly longer fixing time (up to 60 seconds).

Where you are attaching parts with flat bonding surfaces such as a chimney or dome where the ability to correct position over a few minutes is critical, a two-part epoxy is appropriate. It is also worth noting that the resin is not as prone to heat damage as one might think. It is quite in order to solder to parts that have been glued to the resin, for example handrails to knobs, but best not to dwell with the iron too close to the surface of the resin casting.

You will often be required to drill holes in the resin castings and this is best done by hand with a sharp bit, checking the depth of hole regularly. Most resin castings, unless they are filled with other materials are very easy to drill and work.

Paints in general adhere very well to resin, providing that the surface is clean. Painting may be carried out with enamels, cellulose or acrylics. Acrylic plastic primers in aerosol cans, for example the Hycote brand available from car accessory shops or Halfords own brand, used for priming car plastic parts, bumpers etc., key well to the resin and provide a good base coat for the top colour.