Some Tips on Working with Resin

SOME TIPS ON WORKING WITH RESIN

By Mike Bartel

BACKGROUND

Mike Bartel is the founder and owner of Imperial hobby Products (IHP). IHP is the producer of commuter rail, light rail and streetcar models. He has produced the 1981 Kawasaki Light Rail Transit vehicle as used in Philadelphia, models of the 1946 All- Electric Kansas City PCC car, the Pittsburg sealed windows All-Electric PCC car and, more recently, the 1936 All-Electric PCC car. Mike continues to upgrade his models. Since most of them are available in resin kits, it was thought that his tips on working with resin would be helpful to new traction modelers.

RESIN AND THE MOLDING PROCESS

Resin is a type of plastic. The manufacturing process is different than the common injection molded plastic kits, which is why the parts look, feel and smell different. Do not be fearful of this material. You normal line-up of hobby tools and paints will work to build any resin kit. No extra special skills are required, but there are some things to be aware of when building resin kit, hence the reasons for this lesson.

Resin kits often will offer different detailing than a plastic kit. Because rubber is normally used for the molding material (rather than the hardened steel used for molding plastic kits), certain details with “undercut” can be molded right onto a major part, whereas on an injection molded plastic kit, these details would have to be molded and applied separately. Be aware that some delicate one-piece assemblies may be easily broken during clean-up or installation because of the way that they are molded. Do not get the wrong idea. Resin is a durable material for model kit making, and the assembled model should last as long as any of your plastic models.

As is the case with all model kits, regardless of the material used, the parts will require clean-up. This means some light file work to remove pouring gates and light sanding work to remove any mold parting and flash. Sometimes it may be necessary to use a small razor saw to remove pouring gates. Do this carefully and do the clean-up with small files. In the case of windows or other openings, a thin film of resin may be found within the openings. This happens in the process of molding the part properly. This “flash” is easily removed with medium to fine sandpaper and a small file, or by even scrpaing with a sharp hobby knife if the flash is thin enough. Any imperfections, such as pinholes, air bubbles, and / or small cracks, can be filled or repaired with gap-filling super glue and wet sanded to shape. But, when working with resin parts, be careful not to inhale resin dust. After time, this can be a very unpleasant experience.

Conventional plastic and styrene model adhesives will NOT work with resin. Cyanoacrylate Super Glues, such as Pacer’s Zap-A-Gap or CA4000, must be used. Two- part epoxy cab also be used, but it is a bit messier and slower. When using the super glues, it is important to remember that it bonds almost instantly, so you must have the parts correctly positioned the FIRST time.

Bracing thinner sections of a resin kit is often a great idea. Large but thin resin pieces may warp over time, especially if placed near a heat or sunlight source. This is especially a problem when building resin kit structures. Wood, plastic or metal strips are excellent sources of such support.

Some resin kits may have some of the detail parts cast in white metal. Don’t let this scare you. Just clean the parts well, removing the mold lines with sandpaper and files just has you would with plastic or resin parts. Use super glue to attach the metal parts to the other materials.

PREPARATION FOR PAINTING

All resin parts, once properly prepared for assembly, MUST be washed and scrubbed in soap and water, preferably with an old toothbrush. DO NOT USE HOT WATER as this can cause warping of parts. Washing will remove mold release oils, hand oils and dust. Resin parts often have an abundance of surface oils, which will present problems with paint adhesion unless they are removed.

Speaking of warped parts, warped parts can be usually corrected by dipping the part in boiling hot water and holding the part to the proper shape for a minute or two while it cools. For flat parts, just lay them on a flat glass surface and place some weighted object, such as a large book, on them for a day or two. If this does not work, or the part to too warped (or defective) to use, you should make arrangements with the kit producer to return the part for exchange. In the case of IHP, send the part with an SSAE (Stamped Self-Addressed Envelope) and a replacement will be sent. Most other reputable resin kit producers will respond the same way.

CONCLUSION

You may find that building in resin is easier than you expected, especially if you make notes of some of these tips. It is similar to building plastic kits, except that the material is different and requires different adhesives, such as super glues, for assembly. Some extra patience is required, as some extra time is required for clean-up and preparation for assembly. Resin kits cost more than plastic kits due to the high manual labor required for a relatively small number of kits. But producing the same number of kits in a plastic injection-molding process would be cost-prohibitive. That is why only one model of a United States Light Rail Vehicle has been injection-molded in the last thirty years. So since the subjects modeled in resin are for a smaller market, be on the lookout for that “odd” model. You can even find the answer to that plastic kit problem by working in a different medium, such as resin, and seeing the same problem from a different angle. And in many cases, the companies that produce resin kits are not big corporations. They are small, in many cases one-person operations. There fore, your comments and suggestions will be heard and in most cases, welcome.

We hope that your first resin kit will not be your last. Happy Modeling!

RECOMMENDED TOOLS FOR RESIN KIT ASSEMBLY

XACTO or other hobby knife and replacement blades; Small files, round, flat, half-round, triangular and edge; Sandpaper, coarse, medium, and fine grades (wet or dry); XACTO or other razor saw with fine and medium cutting blades; Super Glue such as Pacer’s Zap-A-Gap cyanoacrylate adhesive or CA-4000. Small twist drills and a pin vise to hold them.

These tools will enable you to assemble most resin and plastic kits. A sanding block can be useful for sanding flat parts. This block can be made by using self-adhesive sandpaper and fixing it to a black of wood or metal. The paper can be replaced as it wears out.