Source: http://www.oocities.org/Pentagon/6985/casting.htm - Updated: 10/22/1998

Casting and Forming

Contents


Introduction to Casting

Check out smooth-on.com. They have pretty decent instructions on various types of mold making. In addition, they produce molding and casting materials; silicones, urethanes, etc. They also have a list of distributors for their products. You're not likely to find these things in stock at your local hardware store, so you'll probably have to mail order them.

Most folks make molds out of silicone because it's fast, relatively easy and produces good results. It is more expensive than urethane or latex though. With silicones (and urethanes) you need a triple beam scale, because the mix ratios are usually by weight and you can't eyeball them. Try, and you'll end up with a gooey mess. Silicones vary by hardness and elasticity (among a slew of other specifications). Generally, the softer the material, the easier it is to demold, but the fewer pulls you'll get from a mold. It's a good idea to have a vacuum chamber to degass silicone before pouring so your mold won't have bunches of air bubbles.

Silicone molds can capture deep undercuts that are problematic with rigid metal molds. However, silicone molds don't last for much more than 50 copies.

For casting, most people use rigid polyurethane resin (like Alumilite, Ace, or Synair Por-A-Kast 2). These are pretty easy to deal with because they mix in a 1:1 ratio by volume, and cure within about 3 minutes. For casting rubbery things -- I haven't really sampled very many products so I can't recommend anything specific. I have used some compounds distributed by Burman Industries, but they're too soft for boots -- intended to be used for fake flesh (BJB F25?). All in all, these products are really moisture sensitive and prone to trapping bubbles. Ideally, for solid pieces you'd use a pressure pot to compress the bubbles while the material cures. You'd want to cast something like a boot while rotating a one-piece mold so you get a "skin" instead of a solid boot-- this would steer you in the direction of a quick curing compound. Many of these compounds have a gel time in the neighborhood of thirty minutes to an hour (longer than you'd want to manually rotate a mold), so that should simplify your search (and subsequent trial & error) somewhat. Unfortunately, sample chips do not come in the form of a GI Joe boot.

A final caution -- the materials have a fairly short shelf-life -- six months to a year. Once you open them, they start to degrade. And they aren't cheap. A gallon of GI1000 silicone costs approximately $115. You can usually buy in pints, but it costs more per ounce. So have your stuff lined up before you buy supplies. I'm assuming that you've already taken the time to sculpt or kit-bash your master patterns, right?

I'm providing this basic information hesitantly, so it's up to you to read, learn, spend & experiment.

Unfortunately, I've become jaded by the evil stuff that many humans use this knowledge for. Instead of u"sing it as an adjunct to creating, it's often used as a quick way to make a buck and cheat the creators out of what's due. -- Jimbob


30 Minute Disposable Vaccuum Former

Principles of vaccuum forming styrene

Heating a sheet of styrene (standard modeling plastic) to the point that it is soft and flexible, then shaping it down around a model master by applying a vaccuum from underneath.

This is the cheapest, most ugliest vaccuum former you can make, but it works perfectly every time, and it's easy to make and use.

Materials

First thing is to get the materials. All of them are available at your local home supply store and local craft/hobby shop. The vac former will cost right at 10 dollars, and the Evergreen brand sheet styrene usually runs about 2 bucks a pack depending on sheet thickness.

  1. You'll need 2 pieces of oak planking, 2 inches wide x 1/4 inch thick x approx 24-36 inches long. This is what your vaccuum former box is made of, so plan how big you want to do it and buy enough wood to suit. The 24 inch long oak pieces will run approx 2.50 each at Lowes, and are sold in the flooring section and the hobby section. Pine works ok, but get it in thicker pieces since it may warp/scorch when heat is applied.

  2. Next, a piece of 1/4 inch thick pressed particle board as big as your box is planned to be. That's your box bottom.

  3. A piece of wire window screening cut to fit into your vaccuum former box.

  4. Some liquid latex or rubber cement to serve as your sealant

  5. A box of thumbtacks or wire tacks to hold your styrene in place.

  6. A bottle of glue. Cyanoacrylate is best if you're in a hurry; Elmer's or carpenters glue if you're not.

Construction

  1. cut your oak planks to the size your box will be. The last one I made was 12 inches long and 6 inches wide.

  2. Securely glue those on edge to your baseboard, with all the ends butted tightly against the others. That forms a box that is 12 inches long x 6 inches wide x 2 inches deep.

  3. Run an extra bead of glue along all the seams to seal them, and let it all dry.

  4. Cut a hole in the baseboard for your vaccuum hose. Take the accessory hose from your vaccuum cleaner and trace the end onto your baseboard and cut it thru. Make it a snug fit.

  5. Tack the piece of wire window screen down to the baseboard inside the vaccuum former box.

Use

  1. Take your model master and secure it to the baseboard inside the box. Sculpy or fimo works perfectly.

  2. Run a bead of liquid latex or rubber cement around the entire top edge of your box, and thumbtack a sheet of styrene down over it. Try not to leave any styrene overhanging the edges. It will melt and waste the styrene.

  3. Heat your kitchen oven to approx 300 degrees. The temperature isn't critical since youll be watching it the entire time.

  4. Place the vaccuum former box on the top rack with the oven door open!

  5. Keep an eye on it. The styrene will melt in a matter of seconds!

  6. You should have your vaccuum cleaner right beside you in the kitchen and turned on right now.

  7. When the styrene tacked to the box begins to sag and get wavy, it is melted. Take the box out of the oven. The box won't be hot enough to need a pot holder. It's been in the oven 20-30 seconds.

  8. Immediately insert the vaccuum cleaner hose into the hole you cut in the back of the baseboard. The melted styrene will vaccuum down over your model master and youll have your first vaccuum formed item. Congratulations.

  9. Inspect it to see if its ok before you remove the styrene from the vac former!

    If the styrene didn't vaccuum down completely, you may need to let it heat/melt a bit more the next time. You can put this same one back into the oven again and let it melt a tad more this time before you vaccuum it. The oven heat will cause the used styrene to melt and relax back to its original shape. You can heat/vaccuum the same piece of styrene several times until its right. Just leave it sealed on the vaccuum former until you're satisfied.

    Also try using different thicknesses of styrene. Thicker ones melt slower.

    Improvements

    For a more permanent, or more used vaccuum former, consider making a top frame from 1/4 inch square oak strips, and hinge it onto the vaccuum former box you made. I route out a groove in the box top edges, and glue a length of nylon window screen rubber grout into it to use as my gasket/sealant. To use it, simply clamp the sheet of styrene down with the hinged frame and use as above. No latex or rubber cement is needed. -- Richard A. Lewis


    Using the Vaccuum Former to Make a Helmet

    1. Take a resin head you've cast, or a scrap commercial head (it will be destroyed most likely, so use a scrap one), and sculpt your helmet master directly onto the head with sculpy or fimo.

    2. Spot glue it with cyanoacrylate to a pizza pan or oven safe plate - neck down, standing up, so it doesn't flatten on one side if its laying down.

    3. Bake it in the oven as the modeling clay package says,

    4. When its cool, sand it reasonably smooth. The finish on the master isn't really important in vaccuum forming, but add more clay and bake it/sand it until it's the correct size and shape.

    5. If you used a resin head for your master, it will be ok to vaccuum form directly over it. If you used a commercial plastic head, then gently remove the melted head from your fimo master and fit that master down over another head. It won't be damaged in vaccuum forming, so its ok.

    6. Fix the head/helmet master to the inside of your vaccuum former you made and have at it.

    A single sheet of styrene runs about .50 cents, so that one helmet will cost about .50 cents to make.

    If you decide to make several helmets from that one master, then consider casting that head/helmet master out of resin a dozen times or so. Glue all those resin masters on a piece of particle board side by side, about an inch between each of them, and vaccuum form them all from the same sheet of styrene. A 12 inch x 6 inch sheet of styrene can do approx 12 helmets if vaccuumed all at once, so those helmets are only about 5 cents each.

    As the last step to producing a helmet, simply make an interior webbing for the helmet and you have an accurate, detailed helmet of any type/style you choose. As an alternative, simply stick a small piece of sculpy on the inside of the helmet to keep it spaced up off of the head realistically. -- Richard A. Lewis


    Casting a Head

    The easiest way to do a mold is to kneed the modeling media until its soft and flexable and encase the entire head in a ball of it, making sure to press it into the features. Talc powder is the only mold release you need, but be sure to powder the head well before applying the clay. Then sit it in a cool spot for an hour or so and the clay will restiffen. Then take an xacto knife and cut along the sides of the ball of clay all the way around to form a 2 piece mold. You then fire it in the oven for approx 30 minutes for the fimo.

    To use that mold you just made, wait for it to cool and then talc the interior of it - front and back Take a small ball of softened fimo and press it into the facial features. Do the same with a ball of fimo in the hair part of the mold. Use an xacto knife to level the fimo in both sides of the mold and press them together.

    Rubber band it in place and sit it somewhere cool to stiffen back up. After a few minutes, you pull the mold apart and you have a perfect copy of the original head that is still flexible enough to sculpt.

    When you're done with the modifications you plan to do, simply pop it into the oven and cure it. After the piece is cured properly, it will be quite hard and very permanent, but still have a tiny bit of give to it so that it won't chip or fracture as resin sometimes will. It's also not as toxic as resin or as messy and smelly as latex and resin are.

    Latex and resin are great if the head you want is pretty close to the original, but sculpy and fimo allow you to modify the piece before curing it. -- Richard A Lewis

    Sculpt your head with Roma Plastalina clay. Sculpy tends to be hard to manipulate to exact specs. Roma, an oil based non-hardening clay, is professional modeling clay. It comes in big grey or white blocks and 4 hardnesses.

    Cover your clay head sculpt with Clear Coat (a spray that's sold in art stores for pastel drawings) then cast your 2 piece silicone mold over that. Then you can cast hard plastic positives out of the mold for a professional end product. -- Sean


    Using a Mold

    If you have the master done then you can go two ways with the molds, you can use silicone RTV rubber. This sytem will require you to make a two piece mold so if you don't mind cleaning up a seam then this is a way to go. I like it because you don't need a mold release and pulling the finished piece out is a snap. Call Alumilite Corporation (616) 342- 1259 and they'll tell you the best type of RTV to use, ask for their booklet on how to make a two piece mold.

    The second way is the one piece latex rubber It takes a while to make because you have to brush on the latex in layers at a time waiting for each layer to dry before each coat. If you got the time this is a less expensive way to do it. If you havn't tried it use Sculpey 3, FIMO requires some kneading before it's workable. I recommend this for the beginning sculptor. Another thing to keep in mind is you might want to make a plaster support mold for the latex mold. This insures that the head will not come out mishaped specially if the piece you want to reproduce is large. Your local craft shop should also have a booklet on how to make molds using latex rubber. -- Robert Decastro


    Rob Sorrels Resin Casting Instructions

    TOOLS, EQUIPMENT, AND STUFF REQUIRED:

    1. MAKING THE MOLD Safety equipment (glasses, mask, rubber gloves, etc), Disposable paint brushes, Liquid latex rubber, GI Joe head, Cardboard, Glue (Superglue, Elmers, etc), Baby powder.

    2. MAKING THE RESIN COPY

    Safety equipment (glasses, mask, rubber gloves, etc), Mixing cups (I use measuring cups for this), Popsicle-type sticks, Toothpicks (sometimes), Resin & catalyst.

    3. FINISHING THE RESIN COPY

    Safety equipment (glasses, mask, rubber gloves, etc), Hobby knives (X-acto or equivalent), Rotary tool (Dremel or equivalent) with selection of bits, drills, etc., Sandpaper, A template with a bunch of different size round holes in it (office supply store should have them), Rubber O-ring (Size #91 - 11/16x7/16x1/8 for males heads), Wire, Acrylic paints, Clear (matt, semi-gloss, or flat) spray paint or lacquer.

    Before getting into the "meat" of this article, let me caution you that some of these procedures, equipment, materials, etc can be dangerous if you don't use caution. PLEASE be careful, use safety equipment, and think about what you are doing before you do it. This should be fun, and a trip to the emergency room is never fun!!!

    I. MAKING THE MOLD:

    1. Take the head (that you want to copy) off the body. Usually you can just twist and pull and it will come off. You may need to warm it up to make the plastic a little more pliable. Marx heads can be removed by first removing the spring holding the arms to the body. The Marx head will slide out after you remove that spring.

    2. Using your glue (I like to use gap-filling superglues), glue the head neck-down to your cardboard. I like the cardboard to be about 6" square so I can pick it up easily as I work with it. To duplicate Marx heads you will need to cut a hole in the cardboard for the neck to fit down into since the Marx necks are about 2" long! I use electrical tape on the bottom of the cardboard to hold Marx heads to the cardboard.

    3. After the glue dries, start painting on the liquid latex with your disposable brush. Make the first coat thin and make sure you get the latex into all the little nooks & crannies like the nose, ears, eyes, etc. Be sure to cover the entire head and paint out onto the cardboard into a circle about one to two inches around the base of the neck. Let this first coat dry for at least a half-hour. Throw away the disposable paint brush, it's too much trouble to attempt to clean out the latex!

    4. Keep applying thin coats to the head and the area around the base of the neck. Try to get even coverage over the entire piece. Allow at least a half-hour between coats so the latex has a chance to dry. Setting the piece in front of a fan will help speed-up the drying process!

    5. Apply about a dozen coats to the mold-to-be. After the last coat, allow the mold to dry for at least 24 hours.

    6. After letting the mold dry/cure for at least 24 hours, dust it well with baby powder. This will keep the latex from sticking to itself as you take it off the head.

    7. Carefully peel the latex away from the cardboard around the edge of the mold. Peel it away up to the head all around. Dust the freshly exposed latex with baby powder.

    8. Now firmly grasp the base of the mold with both hands, put a thumb on the top of the head, and peel the mold off the head. Pull on the base of the mold as you push with your thumb. Allow the mold to turn inside out as you take the head out of it.

    9. Dust the inside of the mold with baby powder. Turn the mold right-side out. The mold is complete at this point.

    10. To make the mold tougher you can bake it in your oven, but I've never felt the need to do this. As you cast the resin copies, the resin curing will generate heat and cure the latex so that it'll get tougher over time. Eventually the mold will rip, tear, or just generally break down to the point you'll need to make another one. Some of my molds have broken down after only six copies and others are still in good condition after almost 20 copies.

    11. To make a cardboard support for the mold, take two pieces of cardboard that are about 6" square and cut a "U" shaped cutout in one side of each (see below for a crude idea of what they look like) but smaller than the circular base of latex. Also make the "U" channels long enough so that when you slide them together around the neck of the mold, they overlap a bit. When we turn the mold upside down to pour in the resin, the mold will rest on these pieces of cardboard. I use clothespins to keep the cardboard pieces together where they overlap.

    II. MAKING THE RESIN COPY.

    1. Put the cardboard supports around the mold. Place the mold, head down, on a cup, mug, or other suitable (and sturdy) holder.

    2. Mix the resin per the instructions that came with it. Use a popsicle stick to mix the resin in an appropriate size mixing cup.

    3. Pour resin into the mold until it is about half full. Turn and rotate the mold to get the resin in all the ears, nose, etc. Take the popsicle stick that you mixed the resin with and poke it around in the mold to break up any air bubbles in the nooks and crannies. Don't poke so hard you bust the mold, just enough to get the resin into all the small spaces. The usual places air bubbles appear are on the ears, nose, and chin. Finish filling the mold with resin. Poke around (massage!) the ears, nose, etc to get all the bubbles out.

    4. Let the resin cure for about a half-hour or so. The mold will be warm due to the chemical reaction of the resin.

    5. Remove the resin duplicate from the mold in the same manner as you removed the original head. If you attempt to do this too soon, the resin will distort. If you do this after the mold cools down, you'll have a greater risk of tearing the mold. After practice you'll figure out a good time interval to allow before pulling off the mold.

    6. Let the resin copy continue to cure. I usually let mine cure overnight. Put it on a piece of cardboard, newspaper, etc to cure.

    7. The first copy from a new mold is usually trash. The baby powder that you use to keep the latex from sticking to itself is picked up by the resin and ruins the finish of the first duplicate. I just plan on tossing the first head into the trash. The heat from that first copy cures the latex enough so that it doesn't stick to itself as readily as fresh latex does.

    8. Let the mold cool completely between casting copies. It will last longer that way. Remember the heat toughens the latex.

    9. I use cheap plastic mixing cups to mix my resin in, and popsicle sticks to mix it. After pouring the resin into the mold, I just let the excess resin cure in the mixing cup. Once it hardens, you can flex the mixing cup and the excess, now-cured, resin will pop right out. You can also leave the popsicle stick in the excess resin and use it as a lever to help get the cured stuff out of the mixing cup. If you wait for the resin to cure, clean up will be a breeze!

    10. If you have too much resin left over from one head mold, and you don't want to waste it, you can pour it into another mold and leave it there. Later when you have more resin left over, you can pour it into the same mold, on top of the previous resin (now cured). A nice property of resin is it will stick to itself so well you'll think it was poured at one time. I had my router grab a head I was working on and it pulled the head out of my hand, spun it around a few hundred times and threw it across the room. It ricocheted all around the hard floor and concrete block walls. It turned out to be a head that I had poured from two different resin batches like described above. No damage at all to the head! (This also illustrates why safety gear is required!)

    III. FINISHING THE RESIN COPY.

    (NOTE: mounting technique applicable to HOF and CC Joes, others will require different techniques!!!)

    1. If you use the same type resin I do, finishing the copy is fairly easy. The resin works just like styrene plastic. Start by sanding the base of the neck flat. Place a sheet of medium or course sandpaper on a flat surface, then just rub the copy back and forth until the base is flat and at the height you want it to be.

    2. If you're making copies of old Marx heads, you'll need to use the sandpaper and/or hobby knife to clean up the mold line that Marx left on the heads. If you don't want to do this with every new copy, then use a cleaned-up copy as a new master and make a mold from it.

    3. Take the template with all the round holes in it and find the hole that is just a tiny bit larger than the mounting peg you will be mounting the head onto. Place that hole over the bottom of the neck and center it up. Use a pen or pencil and draw that circle on the bottom of the neck.

    4. Take your Dremel tool and using a drill bit, drill a series of small holes around the inside of the circle you drew on the bottom of the neck. Make the drill holes longer than the height of the body's mounting peg.

    5. Put a barrel-shaped router bit on the Dremel tool and use it to router out the neck and head to the diameter of the drawn circle. Make sure the hole is deeper than the mounting peg is tall. The head should fit loosely over the neck peg at this point.

    6. About 1/8th inch from the base of the neck, router a slightly deeper edge around the inside of the hole you made in step 5. A cone-shaped bit is best for this. This slightly deeper portion is where the rubber O-ring will eventually sit. The inside of the neck should look something like this:

    7. Put a rubber O-ring on the body's neck mounting peg.

    8. Wrap a small piece of wire around the mounting peg, above the O-ring. The idea behind these last two steps is that the O-ring will fit into the small groove we made in step 6 and hold the head onto the mounting peg. The O-ring's inside diameter is larger than the peg's diameter so it allows the head to flop around on the neck. The wire wrapped above the O-ring keeps the O-ring down tight on the bottom of the mounting peg and keeps the head snug so it won't flop around. The O- ring mounting allows the head to turn side-toside just like the original. Some folks cast the heads directly to the body, but that eliminates the articulation.

    9. Test fit the head to the body.á Make any adjustments necessary to get the head to fit snugly onto the body. Then remove the head for final finishing.

    10. Wash the head well with dish soap. This will get your finger oils off the head and help the paint to stick better.

    11. Paint the head with acrylics.

    12. Allow the acrylics to dry well, then spray the entire head with clear spray paint.

    13. Allow the spray paint to dry well (usually overnight) and then mount the head back onto the body.

    14. Dress your new troop and enjoy!

    MISCELLANEOUS RAMBLINGS ON RESIN CASTING

    1. I use resin from Ace Resin, 7481 E. 30th Street, Tucson, AZ 85710-6338 website: http:\\www.crystaltower.com/aceresin Like I said earlier, this is easily workable with hobby tools. If I want to make several duplicates with changes to the original head, like removing scars, mustaches, etc, I make a mold of the original, then cast a good copy. I take that copy and make any changes to it that I want, then use it to make another mold for the changed head. I can now use that mold to cast a bunch of heads different from the original. Some of the ones I've made are: Sgt Savage without the bandaid on his forehead, Roadblock without his beard & goatee, Marx Silver Knight without goatee, and the CC head sculpt without hair (bald).

    2. Don't put any unfinished resin parts on your furniture. I did one time... when I picked it up again a few hours later, the furniture's finish came up with the head... down to the bare wood..á my wife loved that... :-(

    3. The resin takes about 3 - 5 minutes to begin to set up. You have about that amount of time to get all the air bubbles out of the mold. If you wind up with a bubble, when you take the copy out of the mold it will have a hole in it where the bubble was. You can fill this hole with model putty or even auto body putty if you want to save the head.

    4. Ace also sells RTV mold-making material. This is a two-part liquid rubber material that you mix together and then pour over your item (in a suitable box to contain the mess!) to make a moldá I haven't had much luck making molds with this stuff, and it's many times more expensive than the brush-on latex! I get my latex from Hobby Lobby and it costs about $10 for enough to make approximately 25 - 30 head molds.

    5. The cheapest brushes I've been able to find for mold-making are the ones with plastic handles that you can find in hobby storesá I found a great source called "Everything's a Dollar" where I get a pack of 24 brushes for $1.00. That's enough for two head molds. Hobby Lobby also has brushes like this, but they get a few more cents for theirs. I also got my cheapo measuring cups that I use to mix the resin in from Everything's a Dollará Hobby Lobby sells popsicle sticks in a box big enough to last you for several years, or you can get them in small sizes, too. You can also save them from your popsicles and/or fudgesicles! ;-) -- Rob Sorrels


    Using Sculpy

    I used sculpy to make a mold for the Fender logo on my amp. It worked with the polyester resin that I used. You need to use a mold release on it! -- Jerry Brownlee


    Miscellaneous Comments

    The problem with a rigid outer over a latex inner mold is getting the molded piece out afterwards. The mold has to be flexible enough that the molded piece can be worked out of the latex mold after its finished. A solid one piece plaster casing won't work. The two piece plaster mold casing works perfectly but you have to be absolutely sure you get the plaster casing lined up over the latex inner perfectly, or the plaster casing will deform the latex mold and ruin the piece. I get around this problem by attaching a few index pins made of this styrene rod to the latex mold and latex over them to secure them to it. When you replace the plaster casing each time you are ready to mold something, simply get the pins into the corresponding holes in the plaster casing. Rubber band the two piece plaster casing together and you're all set. -- Richard A Lewis

    I tried my first head mold with liquid latex. It work pretty well, but the jaw balloned out. Suggestions?

    Apply three or four coats to the head and let them dry, then apply the next coat and layer it with a single ply of gauze. Do the same for the next coat as well and you'll have a pretty permanent mold. One thing, some latex mold making material requires vulcanizing to properly strengthen and cure the mold. If yours does, then follow the directions and boil the mold in water for however long it says. -- Richard A Lewis

    The best thing to do is make a mother mold (out of plaster) to keep the latex mold from shifting in shape. This can be two pieces. You can even use plaster bandages for it. This should keep it from moving at all. -- Sean

    I had the same problem, except the whole head balloned out. It was pretty funny actually. Part of the problem was the latex mold, it wasn't thick enough. The main reason is that the resin I used expanded a fair amount (foamed a bit). I made a new mold and switched to a different resin. (Alumilite) -- Scott

    Make sure the alumilite not make contact with moisture. Water for instance, even tiny spots of it, will cause alumilite to foam. -- Robert Decastro

    Where can I learn more about doing all this?

    Contact Synair in chattanooga, TN. They sell casting resins (pour-a-cast resin systems) and vidoes on mold making and casting. I recommend "G.I.-1000" RTV silicone rubber for making molds and any PTFE release agent will do (avoid silicone oil based release agents). When pouring the other halve of your RVT mold use a vasoline based release agent on the contacting rubber sufaces only, not on the parts. -- Jim