Cast resin parts can be a great alternative for the budget builder. They are much less expensive than the metal originals that they are cast from, are relatively available "on demand" and can be made to order when you want them. I use an ultra-low viscosity casting resin that yield castings that are bright white and virtually bubble free. Vacuum degassing is not necessary with this type of casting resin meaning your parts will have little to no bubbles in them. Some pieces are cast under pressure to further reduce the chances of bubbles that can become trapped within undercuts inside the mold. Fully cured castings are tough, durable, machinable, and paintable. They resist moisture and mild solvents making them an ideal medium. The following text contains tips and recommendations on how to use your resin parts.
-PHYSICAL CLEANING AND TOOLING-
Resin parts can be SANDED, SAWED, DRILLED, and FILED as required. They easily accept screws if pilot holes are properly used. Without the use of a pilot hole, you may crack or split the part due to its density. If you begin to hear a horrible squeak and it becomes almost physically impossible to turn a screw into the material by hand, you may need a slightly larger pilot hole. Drill holes for bolts as well but do not over tighten physical connectors where it is likely to crack the resin under to much pressure. Most of the parts I make do not require a lot of tooling to work with them but some parts may require the removal of extra resin required in the molding process. This extra resin is a result in casting. Some molds require a "gate" or "sprues" in the mold which is a hole or channel in which the liquid resin flows into. When a mold requires sprues, you can always assume it will have a "vent" somewhere else. As the molds are filled, the resin flows up through the sprues, cures, and will look like strange growths or legs on your parts. They are not pretty but the serve the function of casting and without sprues, the resin could not be poured into enclosed two-part molds. They allow air to escape when the mold is being filled so that it doesn't become trapped inside, preventing the mold from being completely filled. If your part has some strange or foreign looking piece of extra material on it that looks out of place, such as modeling clay or a dowel rod, you must remove them from your part before assembly. Parts can also include "Flash" or flakes of cured overflow that are easily removed by hand. Simply sand those areas clean. Parts that will include sprues during casting will be RADAR EYES (Four on the back), ANKLE CYLINDERS (Two on the flat side), BATTERY BOX HARNESS (A small one at the base), The LARGE DATA PORT (One on each side of the back) . The OCTOGON PORTShave a small base around them of extra material to reinforce them during casting. You will only need to remove the extra material from the bottom side that sits on the floor of the body inside your droid. I have placed the sprues so that they do not effect the cosmetic appearance of the part and can easily be removed using small hobby saws or a DREMEL tool with a high speed cutting attachment. Always use caution and take the proper safety precautions when working with power tools. Use safety glasses and a dust mask when using the high speed cutter or electric sander. You will generate a lot of airborne dust particles or flakes which can be harmful to your health. I also recommend that if you are using a DREMEL tool with a high speed cutting attachment that you take your time grinding away at the resin. If you press into the material too hard, this will make the tool dig in and produce a lot of heat and smoke. If you begin to see this, back off the material and slowly chew at it instead. You definitely do not want to be breathing in any of the dangerous gasses that high heat produces when grinding on resin. For best results, please use caution and do not generate a lot of heat.
WORKING WITH RESIN PARTS
-THIS TEXT CONTAINS IMPORTANT INFORMATION REGARDING THE PROPER USE OF YOUR PARTS-Failure to read and follow this information may lead to undesirable results.
In some cases you may want to sand your parts when you are filling pinholes or removing flash. I recommend using the wet sanding technique as it washes away the dust from the part and you can keep a close eye on what you are doing, giving you better control. Be very careful when sanding your parts, you can remove a lot of material very quickly and if you are not careful, you may sand off way more material than you need to. By using the wet sanding technique, you benefit by not breathing in the harmful dust created from dry sanding. Use a dust mask if you must dry sand your parts to prevent breathing in the material. I tend to use sanding cloth or emery cloth. I find that it lasts much longer than paper backed sanding materials. it can be ripped into different sections that you need quite easily but will remain strong during wet sanding. It can be found in all the standard grit varieties as regular sand paper and is usually found where automotive cosmetic tools and supplies are sold.
-USING ADHESIVES AND FILLERS-
Pinholes and gaps can be easily filled using Bondo, fiberglass, and a variety of spot fillers designed for auto body repair. Some adhesives such as J.B. WELD also make good fillers. it is always easier however to fill a bigger hole than a smaller one so if you have a tiny area that needs filled in, it may be easier to open it up a little bigger with a hobby knife or DREMEL tool. You may want to score the area with the blade or sanding paper to help the filler material stick where the resin is smooth. You will have a much better bond between the resin and the filler material if the area has been roughed up. This is also true when it comes to using a two-part epoxy to bond parts together. Always sand or score areas where you will be gluing to create a good bond between gluing points. In saying this, never glue painted areas onto other surfaces as the bond will only be as strong as the paint on the surface of the part. Allow filler material to fully harden before you continue sanding or shaping of the area.
-HOW TO REMOVE MOLD RELEASE FROM YOUR PARTS-
Assemble all the materials you will need first and place them near your kitchen sink. You will need a BATH TOWEL, COTTON BALLS, A BOTTLE OF ISOPROPYL RUBBING ALCOHOL, DISH SOAP, A ROLL OF PAPER TOWELS AND A TOOTH BRUSH. Group all of your parts on the bath towel next to your sink and arrange your materials so they are easy to get to. Fill your sink with WARM water and a generous amount of dish soap.
-DO NOT USE BOILING OR EXTREMELY HOT WATER ON YOUR PARTS FOR THIS PROCESS-
Using a fresh cotton ball, wet it thoroughly with rubbing alcohol and wipe down each one of your parts in a circular motion. This is to loosen any release agent that may be present. Mold release is silicon based and the alcohol will break it down. Failure to complete this step will not remove all traces of mold release from your parts. You will want to use a fresh cotton ball for each part as the build up of mold release will increase over time. Now place the part into the sink full of soapy water and proceed to the next part until finished. Once all parts have been wiped down with alcohol , Simply use the toothbrush to scrub each part with soapy water. Brush all areas before returning the part to the sink and let them continue to soak until all of your parts are done. You must complete both steps to successfully remove the mold release. Rinse your parts and dry with a paper towel. Once your parts are fully dry, they will be ready for any mild sanding and or adhesives and paint.
-CHOOSING THE RIGHT PRIMER FOR PAINTING-
You have many options when it comes to the choice of primers used on resin parts. I strongly recommend that you use a sandable scratch filler primer typically found in the automotive section of many retailers. I personally use Rustolem's Sandable Automotive Primer on a lot my castings and it gives great results. I discourage the use of "plastic primers" that are specialty formulated for certain types of plastic materials. They did not work well and I have had less than desirable results when trying them. In general, hobby primers tend to lack the desired solvent strength to stick well to resin parts. Another benefit to using the sandable primer is that it goes on thicker than regular primers. This helps to fill any pinholes or scratches that may be present and will give you a smoother overall finish. Apply a light mist coat and let dry before attempting to apply the first coat of primer. This will help the primer stick well to the part. A mist coat should be thin enough to still show some of the white of the resin through it. Sandable primer typically comes in three color choices, a rusty red or terra cotta, black, and lastly, grey. Depending on what brand you use, you will occasionally find white. Ipersonally like using the grey as I find it is an all around neutral basecoat for whatever color you are putting on top of it.
-A WORD ON MOLD RELEASE AGENTS-
I use a spray mold release on certain parts to help in the de-molding process. Not all of the parts I cast require a mold release agent but some parts do benefit from its use. Mold release basically acts as a lubricant that is sprayed onto molds before resin is poured into them, helping them come out of the molds easier. This also extends the life of the mold, and allows for a much cleaner part. It may be impossible to tell what parts may or may not have traces of mold release on them. The most overlooked and critical step in working with resin is to clean the parts and remove any possible traces of mold release before you attempt to glue or paint them. Mold release is colorless, odorless, and may very well be on the parts without showing any sign that it is there. Your parts may appear dry but the release agent can be remoistened via the painting process causing all kinds of trouble. The paint may crack or easily flake off, discolor, orange peel, fish eye, or very possibly, not dry at all. Surfaces should always be clean and dry whenever you glue or paint them. As an insurance to your part investment, please be sure to follow the steps outlines below. Taking the time to clean your parts should not be avoided and will greatly reduce undesirable painting results.
-BENDING AND RESHAPING-
Resin can be bent or reshaped by using boiling water or a heat gun if have something that may need to be reshaped. The BOOSTER COVERS generate a lot of heat when curing and can sometimes warp the "prongs" that form the open U shape at the bottom. This is due to shrinkage that takes place when cooling down after the curing process. This can easily be fixed using very hot water or a heat gun when you need to reshape a part. Never use an oven or any kind of open flame to reshape a part. In addition to possibly destroying the part, you may release dangerous gasses that can be harmful to you. If you do plan to use a heat gun, use caution as parts can become way to hot very quickly and you may easily scorch the part before you realize what happened. The best method I have found is to boil water and immerse the part into it. Let the part get warm and gently bend it in stages until the desired position is achieved. Keep in mind that large pieces require longer immersion times. Always wear protective gloves as the resin can get quite hot. it is a good idea the then immerse the part in cooler water once you have positioned it where you want it. Just run it under the faucet on your sink. Considering that resin parts are sensitive to very high heat, never leave your parts in excessively hot temperatures. I have seen parts warp out of shape from being left in the car on a hot summer day.
This should cover the basics of working with resin parts. If you take your time and get to know the properties of the material itself and what you can do with it, you will quickly learn that it looks harder than it really is.
-USING CYANOACRYLATE AND ACTIVATOR-
Cyanoacrylate or "Super Glue" works well bonding resin to resin but not as well as two-part epoxies such as J.B. Weld. It does however fill holes and gaps quite well and when used with activator, you will be able to fill them at a much faster rate. When using two part epoxies, you must wait up to eight hours before you can effectively sand it down again. Cyanoacrylate glue and a spray activator will cure almost instantly and can be "built up" until you fill the gap or hole. The activator is a small spray bottle of liquid that instantly cures the Cyanoacrylate. It will smoke and sometimes pop as it becomes very warm. This glue is found at most hobby and model shops and typically comes in three thicknesses consisting of THIN, MEDIUM, and THICK. The Activator will be sold separately and is typically found where model car and airplane kits are sold. It is usually available in what looks like a small spritz bottle and may be packages in a clear tube or small spray can. This stuff is really fun to play with but be careful when using it. Cyanoacrylate can instantly bond your fingers together and it can get hot enough to burn your skin when it does. Play with different glue thicknesses and try to fill gaps on some scrap material first until you get the hang of it. I have found overall that the MEDIUM and THICK work the best. Instead of trying to completely fill a larger hole in one shot, try to fill it in layers. Let the activator do its job but do not over saturate the area that you are filling. You may want to give the activator a chance to dry or evaporate before attempting the next layer. If you are going too fast and activator is present where you bring the nozzle of the glue to the contact point, you may easily clog it instantly as the glue inside will instantly cure. After a little practice, you should have no problems learning how Cyanoacrylate and activator can be the ideal filler for small pinholes and cracks. It is widely used in the model building community for just this kind of application as well as joining small parts. I find that it works much better than other materials and can be easily sanded once cured. Bondo can shrink and crack over time and tends to be very soft. Cured Cyanoacrylate is as hard as the resin itself and if cosmetics are done correctly, will form a seamless blend under paint.