I am often asked, "How is building a resin kit different from a regular styrene kit?", and "Can you tell me how to build a resin kit?" It seems to be feared; a mystical and arcane process for most model railroaders. Well, it isn’t as easy as falling off a log, but if you are willing to try a few new things and invest in a few simple tools (some of which you may already have) then you can learn to build resin cast models, sometimes also known as ‘craftsman’ kits. And you’ll find they are very rewarding to build as well.
By way of explaining the difference between commercially made mass produced styrene kits and short-run resin craftsman kits, lets start by looking at how they are made. A styrene kit, usually offered by large model companies like Walthers or Athearn, is mass-produced in lots of tens of thousands. Engineers and machinists spend many hours to develop a highly-engineered model and cut the molds for it from steel or aluminum. It is a high-speed process where heated styrene plastic is injected into those molds under high pressure over and over again. All of the labor and machinery is expensive to pay for, but because of the speed of production and the volume of models produced the individual models can be sold at relatively low prices and the company still turns a profit.
A resin craftsman kit, on the other hand, usually comes from a garage based business with one or two people who do everything. They can't spend tens of thousands of dollars on sophisticated tooling and expensive injection-molding machinery. In many cases simple RTV rubber molds are made from hand-crafted parts, made by a modeler just like you. A two-part resin plastic is mixed and poured into the molds, which takes time to set up. Often only a few sets of parts can be made in a day, maybe 15 or 20 full kits on a good day. Production runs are far shorter, often running from 250-500 kits, often far less.
Of course the real difference is in the offerings of the two companies. The big professional company can make the same model available to nearly everyone who wants one, but it has to have wide appeal or the economics don't work. A resin kit producer serves the smaller niche market where the big boys can't go. They can offer the special, the unusual, the limited interest models the big guys can't afford to touch. They make it possible for you to get a wider variety of models you'd otherwise be unable to get but for kitbashing and scratch-building yourself. And even with all their expenses (resins and molding rubber aren't cheap), they manage to keep the resin kits price-competitive with the injection-molded styrene kits.
So now we know why the kits are different. Let’s talk about how to build a resin kit.
Resin kits are a little different from the styrene kits you are probably used to. Unlike styrene molding, where pellets are heated into liquid and forced into steel molds under high pressure, resin is usually a two-part liquid polyurethane plastic that is mixed and then poured into a mold. The liquid resin goes through a chemical reaction that links the molecules into long polymers, solidifying it. Where the styrene process which is completed in seconds, the resin process usually takes from 5-30 minutes, sometimes longer, per set of parts. As you might expect, the polyurethane (PU) resin castings have different properties than good ol' styrene.
For one thing, resins can't be bonded with styrene glues. Testors, Tenax 7R, even MEK or Acetone won't do a thing to PU resin. The preferred glues for working with PU resin are Cyanoacrylate Cement, also known as Superglue, CA, ACC, Krazy Glue and others; and Epoxy. (I will refer to cyanoacrylate as CA for the remainder of this article.) Both CA and epoxy have their weak and strong attributes, and often one or the other may be called for even in the same model. Epoxy is super strong, but it takes time for the bond to set up; anywhere from 5-30 minutes depending on the type you buy. This means clamping or taping parts together so they won't move while the glue sets up. CA on the other hand sets up in seconds, faster if you use a 'kicker' that sets it instantly. But CA doesn't have much shear strength (parts can pop off if stressed from the side), and can fail completely if exposed to cold conditions. I use both depending on the situation, and try not to leave my models in the trunk of the car during winter months. :)
You also need to be really careful about keeping your fingers away from the joint area while the glue is active or you'll quickly find the model glued to your fingers. Don't panic, acetone (nail polish remover) will free you quickly, but you may want to wear safety glasses when working with this stuff, as gluing your finger to your eyelid is much more delicate operation to handle. Not to mention the fumes are quite strong and irritating to the eyes at times – which is what leads to touching your eyelids when you shouldn’t.
(If you use CA to assemble your resin models you can take advantage of one interesting chemical feature - Acetone doesn't bother PU resin, but it is a solvent for CA. If you make a mistake you can brush acetone onto the joint and it will dissolve the CA glue, letting you take the joint apart and try again. Try that with styrene! You can also use acetone and a Q-tip to scrub the glue residue off the model after you get your finger unglued from it.)
Opening up your first resin kit may be a surprise if you haven't seen one before. What you will usually find is a bunch of flat parts that may have a lot of flash (paper-thin extra resin that squeezed out of the mold when the part was made), extra parts for details made from resin, styrene, pewter or brass, wire, a sheet or two of instructions, and possibly decals. Some kits may include one-piece body castings, which are much simpler to build and make life a lot easier. It's quite intimidating on first glance, but you can do this! It isn't as bad as it looks.
Your very first step should be to read through the instructions carefully and completely. I know most of us are guys and it's a pride thing, but swallow it and suck it up! It's often very important to do things in the prescribed steps or you may regret it after. There may also be suggestions of how to do something that may not be obvious and could save you time and heartache later. This is even more critical on models that have lousy instructions - unfortunately there are some like this out there. You'll want to familiarize yourself with all the parts and how they go on the model and when before you start anything.
After reading the instructions, collect all the parts that are not water-adverse and place them in a bowl with warm soapy water. Out of the box, almost all PU resin parts are coated with a slick substance called mold release that helps keep the resin from sticking to the molding rubber. You need to wash this off before proceeding or the glue may not bond the parts together, and painting will be impossible. In some rare cases the parts must also be washed in acetone, it should say in the instructions if this is needed. Clean the parts well (I use a soft toothbrush), rinse in clean water and blot dry with a paper towel.
The next step is to clean up the flash on the parts. GO SLOWLY AND TAKE YOUR TIME WITH THIS STEP. I cannot stress this strongly enough. Resin models are made or broken here. Use a combination of tools - hobby knife, sandpaper, files. You will also want to keep your machinist square handy to check the squareness of corners or the straightness of parts. A steel 6 to 12" ruler is good as a straightedge also.
If you don't have a machinist square, HarborFreight.com sometimes has a nice three-piece set of 2", 3" and 4" squares for less than $8, and they are quite good and accurate - an essential modeling tool. Get their 6" digital calipers often on sale for $10-20 as well; you'll be glad you did. Once you use them you'll never know how you managed without them. They also have needle files and other useful modeling tools as well for fair prices.
I could do an entire article on how to prepare your castings, but let me throw out a few of the best tips I know:
So now you have your parts all ready to go. Follow the instructions and start assembly. Use either CA or epoxy cement as warranted. Use only a little bit especially where the joint can be seen. I have been known to set a joint with small droplets of CA cement applied with a pin or toothpick, then to go back and reinforce a hidden joint with epoxy on the inside after it has set in the correct position.
Thin CA cement can be touched to the joint, and it will wick into the space between through capillary action. Epoxy is a much thicker glue and must be applied sparingly to the mating surface to bond well. Messy joints with glue smeared on the model must be avoided. With either glue the worst thing you can do is try to smear off the glue with your fingertip. With CA it is best to leave it and let it set up, and then sand it off with fine sandpaper. (Or try the acetone trick, but your joint might come apart too.) You can deal with epoxy the same way, but I have heard that 91% isopropyl alcohol on a Q-tip or tissue can be used to clean off squeezed-out epoxy before it sets up. I have not actually tried this. If you do write me back and let me know if it worked or not.
Special clamps can be purchased to hold the parts in alignment during gluing like the Coffman Corner Clamp, but you can make one yourself easily and very cheap with a block of wood and some rubber bands. See the sidebar article by clicking this link. You can even just line up the parts by eye on your workbench, set the angle by leaning the parts against your machinist square and glue them, but you had better know what you are doing. Again, take your time setting up the joint so it is clamped in position before applying glue (or set in position after applying epoxy) and your patience will be rewarded here too.
Unlike the injection molded styrene kits you are used to, resin kits usually don't have cast-on grab irons, or other fine details applied by some 14 year-old Korean girl in a sweat shop. These models are considered craftsman kits, and this is where you earn your stripes as a modeler. These kits often come with a package of separate detail parts you are expected to apply to the car to complete the detailing. It is often the most intimidating part of building a resin kit for beginners, and I won't lie - it will stretch your skills if you haven't done it before. But it is worth learning how to do, it will embolden you to try harder and harder models as you master these skills. Besides, how hard can it be? 14 year-old Korean girls do it all the time.
Seriously now - you will probably be discouraged by your results the first time. Go into it expecting that, but also knowing that it took you a long time to learn to ride a bike too. You can learn to do this, and very soon you will do it well. You can take a lot of the anxiety out of leaning by practicing on an old styrene kit before you actually work on a resin kit. Throw the old styrene car away when you have built your skills up, and no one will ever see the mistakes. Grab irons are cheap, so are nut-bolt-washer castings and after you’ve done a dozen or two you’ll be comfortable with putting them on anything.
The instructions should help you decide when to apply certain details, but common sense should help here too. For instance, it is much easier to put in the grab irons on a boxcar before the floor is glued into place. The brake wheel and underframe levers and wires shouldn't be applied until the model is almost done. Trucks and couplers don't go on permanently until after the model has been painted. The same rules apply for these parts - use glue sparingly and only where needed. Obviously you need to be careful handling the car once you start putting on details like this.
If you don't already have one, go out and get a decent pin vise and a small drill index. Radio Shack sells a nice one with a small bunch of bits that store in the handle for under $15, it's a good choice. You'll also want to get a good index of bits in a storage case from sizes 61-80. And you will want to find somewhere you can get extra bits, specifically in size 77 and 76. You will use these sizes a lot in HO scale for applying wire details. One source is www.microfasteners.com, but there are others as well.
Why buy extra bits? Because I guarantee you will break them, usually one or two per model, especially when you are learning to drill. Get used to it, don't fret over it. Look at them as consumables. It's like changing hobby knife blades (you do keep a very sharp blade in your knife, right?). Wire bits get used up and broken fast. You'll want to be able to throw away the broken bit and replace it in a moment or two without breaking your stride. The last thing you want is to have to use the next size up, or try to drill with the broken edge of the bit. Buy them in sets of 6 or 10, and don't hesitate to order more when you start to run low.
And while you are out buying tools, get a decent needlenose pliers and a wire cutter. At Home Depot you can find a two-piece set of Crescent brand tools with excellent quality pliers and cutters in a blister pack for about $20 - they are also great for hand laying track. These will be extremely useful for working with brass wire often used for grab irons, truss rods and brake lines. Having the right tools will help you have success with these techniques sooner, and bolster your confidence.
In many cases the model will come with formed grab irons, almost always 18 scale inches wide. You may need to plot out where the holes for the grabs go on the side or end of the car. If so, use a sharp pencil and write directly on the side of the car, marking the places you need to drill holes. You will wash off the graphite with soap and water after drilling the holes so don't worry about marking up the car.
You are not ready to drill holes yet. Take a sewing needle (steal one from your wife or girlfriend) and mount it in the pin vise. Don’t use a pin - sewing needles are really hard and really sharp, and you need that here. Carefully locate the tip where you want the hole to be drilled in the resin part, and press it into the resin firmly. What you are doing is deforming the plastic to create a starter hole the bit will center in as you start to drill. This will keep the drill bit from skating along on the surface and making a hole where you don't want it. Some models have divots or depressions already located on the car, I suggest you use the needle anyway - it will work better than not using it. And it is easy to do so why take a chance?
Replace the needle with the appropriate drill bit (usually #77 for grab irons), set the bit into the needle hole and start to drill. Hold the vise between your thumb and middle finger at the center, and place your index finger on the top. Use the index finger to help hold the pin vise perpendicular to the part, and the thumb and middle finger to rotate the pin vise. You do not need to turn the pin vise in complete revolutions. A back and forth motion of about 1/2 revolution or more is adequate to keep the drill working. Try to apply even pressure with the index finger, avoiding side stresses on the bit (which will break it). You don't need to stop pushing down when the bit is rotating backwards. Work slowly and consistently until the hole is drilled through the part. I always set the part on a block of wood so the hole is backed up and doesn't blow out as the drill bit passes through the back of the part.
When applying grab irons, it's usually a good idea to use a spacer of wood or styrene under the rungs to hold the iron a consistent distance from the car side. Set the rungs into the holes, and bend over the back of the wires inside the model to lock it in place. (On a model where the back edge of the grab can be seen, cut the extra wire flush to the back wall.) Cement the grabs in place with epoxy - as a part subject to a lot of handling, CA is too delicate for this.
When separating small castings like NBWs from their sprues, be sure to leave a bit of the stem on the part. This is usually how you are supposed to locate the part on the model. The stem goes into a hole you drill, and then you touch it with a dab of CA before driving it home. It makes for a strong connection without a pool of glue around it that won’t easily be knocked off by careless fingers. Oh yeah – make sure the hole is deeper than the stem or you’ll be doing this again.
Drill out holes for NBWs the same way you did for grab irons, but know in advance that handling the tiny parts can be maddening. I often use the point of a very sharp hobby knife blade to poke them gently, which holds them on the tip, where I can maneuver them into place and slip the stems into the holes. I have heard a bit of sticky beeswax on the tip of a toothpick works even better, I intend to try that out very soon. Any waxy residue should come off in warm soapy water when you clean the model for the final time.
Apply any other detail parts as well, using CA or epoxy where appropriate. Use cement sparingly especially around detail parts, as it will show up when people look closely at them if not applied well. Refer back to the instructions often to ensure you understand how to apply the parts and in what orientation. Once again, go slowly, enough to allow the previous cemented-on part enough time to set firmly before applying other details, making it harder to knock something off as you work on the model.
One thing about resin kits - you'll probably never find one pre-painted in the scheme you want. That's because they almost never come painted! Again, it's up to you to put a realistic finish on the car you have built. This is another area where you will start stretching your skill set and learn to do some new things that will help you in the future.
After construction of the model is completed, you'll want to wash it once more to remove any oils from your fingers or beeswax and pencil marks on the surface. Also some resins may 'bleed' an oily film for some time after they are cast, and these things will keep the paint from sticking well. I wouldn't suggest immersing enclosed cars into water, but a soapy scrub and rinse probably won't trap much water inside. Blot dry with a paper towel and let the model dry out thoroughly before the next step.
Select an automotive primer to coat the model with. Why auto primer? It is designed to stick well to plastics, it is usually a very fine pigment that will not obscure details, it dries very fast, and it provides a good surface for subsequent color coats of almost any kind of paint to stick to. I have heard excellent reviews of Wal-Mart's $1 aerosol primers, which are said to have very finely ground paint solids, great for model work. Primers are available in four colors; white, red, black and gray. Select the appropriate primer color based on the color coat you intend to put on finally, and start spraying. Apply a couple of very light coats of paint rather than one thick coat, waiting about 15-20 minutes between each coat. Stop when there is no exposed resin showing any longer. Paint the top, bottom and sides of the car. Let the primer dry thoroughly, it should not take more than 4-12 hours. Consult the can for better information about drying time.
From here you can paint the model with any type of paint you wish, with brushes or spray paint or airbrush. Primer is designed to be a solid base for most paint, but it might be a good idea to spray a scrap part with primer and test your color coat over it to ensure it will not react badly. Again, if spraying, several thin coats are better than one thick coat. If you are going to decal the model after painting, use a glossy paint or coat the flat paint with a gloss coat before decaling. Dry transfer decals do not require a gloss coat.
Why the glossy finish? Because decals will not go on well over a flat finish. They work best when they can settle evenly onto a smooth glossy surface. Decals applied over flat paint will usually 'silver', or develop silvery areas under the decal film where the adhesion of the film to the paint is poor. Its well worth a thin coat or two of gloss to ensure the decal job looks good, then throw a thin coat of flat finish over that. The final flat finish will not only make the model more realistic, it will protect the decals from being chipped or rubbed raw by handling, and any weathering you do won't build up around the edges of the decal either.
Apply the decals by wetting them, then sliding them off the transfer paper onto the model near where it will be placed finally. I use a paintbrush to pool water under the decal, floating it and making it easier so slide around on the model. When it is in place I touch a corner of a paper towel to the edge, wicking out the pool of water. Then I blot the decal down onto the surface, pressing it gently into the bumps and ridges on the model. I quickly coat the sides and top of the decal with Walthers Solvaset or Microscale's Micro-Set, a solution that softens the decal and helps it snuggle down onto the surface, it also prevents silvering. I usually use 2-3 coats over the decal to set it in place firmly. When the decals are dry, coat the model with the flat finish.
From here, simply add your couplers and trucks to the model, weather it to your taste and put it on the layout! You'll be more proud of every model you turn out that you put your time and effort into, and your friends and visitors will be impressed that you have something unique running on your layout that can't simply be bought off the shelf and placed on the rails. A resin car kit will provide hours of enjoyment in the building and detailing, and dollar for dollar may be one of the best entertainment investments you can make in the hobby.
I hope I've inspired you to try out the world open to you in resin model building. If you are looking for a project, several of the models available from AmesvilleShops.com are excellent candidates for first-time modelers, unique cars that are simple to build and come with clear instructions. I hope you'll take a look at our kits and try one or more out, I don't think you will be disappointed.