Resin Model Preparation

After receiving your model the first task is to unpack it and verify that you have all the necessary parts. If any parts are damaged or missing you should notify your supplier so that they can deal with any delivery or quality issues. Resin models are expensive and you should expect reasonable castings even if you are ordering recast products.

Next, dry fit the parts to determine if there are any assembly issues that you need to be aware of. At this time you should be forming a plan as to how the model must be assembled and painted. Look for ways to fill joints and seams before painting, particularly if the parts can be painted as a unit. You should also think about any required assembly sequence, as parts most often have to be put together in a particular order.

Dry Fitting

The following photos show an initial dry fit of a 1/5 scale recast model of Naru from Love Hina, ordered through E-Bay from a company in Thailand. If you look closely you can see many problems. There are casting issues and fit issues. The most serious problem is the fit of the skirt, as shown.

Repair work is required to correct these defects prior to beginning the painting process. The description of the build process for Naru shows how these faults were corrected.

Now, when I dry fit, I try to pin most pieces together. This means that I drill holes into most pieces and insert small nails or wires that will help secure the pieces together. Pinning the model lets me assemble it before I start to paint it. Pinning also lets me ensure that the pieces will be properly positioned when assembled.

When I first started building resin figure models I didn't think pinning was necessary. But some models have close tolerences for fit and it becomes a real problem to correct fit errors at assembly time. I have also seen some glue bonds become brittle with time. So pinning becomes a self preservation exercise. Once again, the extra time spent at this stage, in preparation, pays dividends at later stages.

Mold Lines and Sprues

On all models you will have mold lines and casting sprues to remove. The following photos are representative of the problems you will see, even on better models. These pictures were taken during the build of Haruka Suzumiya.

	You can see the small sprue at the tip of the shoe that needs to be cut off and sanded.
	Every part has mold seams. All seams need to be sanded smooth. The mold seam on this part runs along the top of the leg, even though it is hard to see. The mold line for the other side is hidden in the back. When you sand these lines do not rub horizontally, along the line. Instead, sand across the line. This cuts away the high part and reduces the risk that you will over-sand the piece as you try to get rid of that last little mark that just won't seem to go away.
	You can also find holes and other flaws in the casting. These have to be filled and sanded before painting. I use a product called Mr. Surfacer 1000 from Gunze to fill holes like these.

Sculpting

There are times when you need to become a sculptor and repair cracked or improperly molded resin. Fortunately most jobs are reasonably straightforward, as shown in the picture below. You don't have to be an artist and create a new part from nothing. All you have to do is mix up a little bit of epoxy resin and repair a broken piece.

I use a two part Tamiya soft resin epoxy. Each part comes in a flat strip like chewing gum. You cut an equal portion off each strip and roll them together so they mix. You can then stick the mixed filler resin to the piece and form it as required.

Look for a resin filler product that can be sanded and sculpted and does not shrink as it dries. You will need to let the filler dry overnight before you try to sand it smooth.

I can't yet advise on more significant sculpting, or 'kit-bashing' as it is called. I have not worked up enough skill to do this, although some modelers are very adept at changing a character's pose.

The best I have done is to heat resin to try and change its shape slightly. The few times I have done this I immerse the piece in boiling water for a minute or two, then try to move it into the desired shape. Be careful if you try this. The resin approaches the temperature of boiling water and you will burn your fingers. Other people have used a heat gun or hot air blow dryer but I haven't tried this yet.

Sanding

You will need three different grades of sand paper - 200 grit, 400 grit, and 600 grit. I use a wet-dry paper because this type of sandpaper is stronger and the grit will not come off the paper quite so easily. You should also know that unused sandpaper is coarser and rougher than used sandpaper, so plan on it and sand lightly when you are using a new piece of paper.

The 200 grit or coarse paper is used to initially sand down large sections of the model such as mold seams or filled areas. This paper will remove material quickly. Sand lightly and carefully because some resins are softer than others. Be careful because coarse paper can easily remove fine lines and other details cast in the model. 200 grit paper on soft resins will remove material very quickly. Don't worry too much if you do remove some detail because you can always redo the lines. I often use my modeling knife with a bladethat the tip has broken off to scratch out new lines.

400 grit or medium sandpaper is used to remove the sanding marks left by 200 grit paper. You must sand with 400 grit paper even if the resin appears smooth. Paint will show the underlying material texture. If you do not remove the marks left by coarse sanding you will see them.

600 grit or fine sandpaper is used to polish the work before painting. This type of paper will not remove any visible flaws so do not expect to correct defects by sanding with fine sandpaper. Your 200 and 400 grit papers do all the actual work. The 600 grit paper is meant to remove the marks left by the 400 grit paper and leave a polished sheen on hard resins. This polished look should be similar to how the piece originally looked after it was cast, as can be seen in the pictures above.

If you require a highly polished surface take some used or partly worn down 600 grit paper and wet sand the work. Keep the paper moist as it will dry out as you work. I put a jar of water on my workbench and soak my paper in the jar before I use it. Wet sanding with a fine sandpaper is equivalent to sanding with a very fine paper.

Thus, you will sand your work not once, but three times and possibly four. Plan on it, take your time, and make sure that all flaws are corrected before you even think about painting the model.

Pinning

So you have this model from hell where the figure is supposed to dance on air or balance on its fingertip? Well, there is only one way to fix this, and that means you have to insert pins in the model to hold it up. Divine intervention simply will not work.

Not only that, but you should really pin almost all your pieces such as arms, legs, heads, and clothes together, too. When I started making these models I didn't bother to pin. Then, I found out later that if you don't pin your model together it can fall apart. Cyano-acrylate cement (super glue) is brittle and the bond will break if subject to shock. Epoxy glue may work better, but the strongest combination is pinning and gluing. If you ever intend to move your model or mail it somewhere then you should pin it for protection.

You can pin things together by using nails with their head cut off, paper clip wire, steel rod, or even wooden toothpicks. Some people claim that pins can rust and eventually stain your model. This may be true for humid climates, but I have never seen this happen in my part of the world. And I try not to get my models wet by playing with them in the bathtub or taking them outside.

The pin adds extra strength to the joint. The pictures below show how pins can be inserted or removed from the model. Simply drill a hole the same size as the pin and jam it into the model piece.

These pictures show a technique called 'blind pinning'. You insert a small pointy pin into the pinhole and then press the pin into its mating part. This pointy pin can be the end of a nail. This pointy part will leave a small mark on the mating piece show you where to drill the matching hole. When blind pinning, make sure that you don't drill too deep a hole for the pointy pin. You don't want to push the pin deep into the part while you are pressing it into its mating piece.

The next problem with pinning is to drill a straight hole in the mating piece such that the two pieces align properly. It's always hard to get one mating hole to be plumb to the other. Fortunately, if you mess up your hole alignment and the pieces don't fit properly, this can be fixed. Simply drill out one of the holes so that it is large enough so that the pieces align correctly. Remember, the other hole is proper sized and will hold the pin tightly. However, before going on, lubricate the end of the pin that fits into the proper sized hole with cooking oil and insert the pin into this piece. Then, fill the drilled out big hole in the mating piece about two thirds full with quick setting epoxy. Put the two pieces together and hold them until the epoxy sets. This will glue the pin in its proper place in the big hole. The cooking oil will also tend to ensure that the pieces don't bond if a little bit of glue gets where it is not supposed to be. Leave the piece to cure overnight. The next day you can pull the pieces apart because the tight fitting lubricated end is not glued. The pin will be now be set in the mating piece in exactly the right place.

There is another way to get your holes to align properly. Simply drill completely through the two parts that are to be pinned. In this case you will have to fill and patch one end of the pin so that it cannot be seen, but you will most certainly have a straight hole for the pin.

Washing and Mounting

All your model pieces need to be washed and polished. Wash your pieces in warm soapy water. I use an old toothbrush to ensure that every piece is clean. Once they are washed you will have to mount the pieces on toothpicks or other supports so that you can hold them during painting. From this point forward the pieces are never touched by human hands and are always held by their mounting supports.

Toothpicks are glued to areas of the pieces that are not going to show. I use cyano-acrylate cement (super glue), as it will actually bond the wood to the resin, even though this is sometimes difficult. If the bond doesn't take, simply try again. It usually takes a few seconds for the bond to form.

Large pieces are too heavy for toothpicks. Use 1/8 inch wood dowel and prepare mounting holes as required to ensure that you have a strong enough support to hold the piece. You may have to drill a mounting hole in the piece. The photo above shows the pieces prepared for Ruri Hoshino.

Summary

Model preparation is tedious and half of the work of building a resin model. The time expended in the preparation stage is critical. PAINT SHOWS ALL FLAWS. If you have pinholes or sanding marks these will become immediately obvious once the model is primed and painted. In fact, you should expect to go back and correct flaws after the model is primed and base coated, because it is difficult to see everything in advance.

The picture below shows that filling, sanding, painting, observing the results, and going back to correct flaws is a constant cycle of activity.