As many of you may have noticed, the “Help!” for Molding and "Help!" for Casting stickies were getting a little out of hand. The same questions were being asked over and over, but it was far too unreasonable to sift through the many pages looking for the answer. So, I sifted through the dozens of posts, looking for the most frequently asked questions. This thread will be those Help! threads' replacement.
As this is an FAQ thread, every single question ever asked may not be covered. If you have a question, read through the FAQs first. If your question is not answered, then you can submit a post asking that question. When someone answers your question (and anybody can answer), the answer will be edited into the question post by a moderator and all subsequent answers/comments will be deleted. This is part of an effort to keep this thread clean and easy to read over. To make it a little easier to locate a particular FAQ, I’ve broken this thread down into sections: Getting Started, Casting, and Molding (more categories may be added later). Determine which category your question falls into and look in that section. Since there is a 10,000 character limit per post, the first 5 posts have been reserved for FAQ expansion.
If you have a question that someone has already posted, but has not been answered, do not post an “I’m wondering that, too” post; simply wait for the question to be answered.
Now, onto the FAQs; there are a lot of them, but this is a complex hobby. Read them (one hint, use Ctrl+F to find a particular word to make your search easier).
What is molding and casting?
Molding or moulding (see spelling differences) is the process of manufacturing by shaping pliable raw material using a rigid frame or model called a pattern.
A mold or mould is a hollowed-out block that is filled with a liquid like plastic, glass, metal, or ceramic raw materials. The liquid hardens or sets inside the mold, adopting its shape. A mold is the counterpart to a cast. The manufacturer who makes the molds is called the moldmaker. A release agent is typically used to make removal of the hardened/set substance from the mold easier. Typical uses for molded plastics include molded furniture, molded household goods, molded cases, and structural materials.
Casting is a manufacturing process by which a liquid material is usually poured into a mold, which contains a hollow cavity of the desired shape, and then allowed to solidify.
Are there any Molding/Casting tutorials out there?
Yes. A Google/Youtube search will yield dozens of instructionals and videos. There are resources outside the 405th; we encourage you to use them if you need them. www.smooth-on.com has a wealth of information as well as supplies most forum members utilize.
I have a boot/shoulder/gauntlet that has an identical counterpart that I have not built yet; would it be quicker to mold and cast a second one, or just build another one?
It depends. If you have the molding/casting supplies on hand, and are familiar with the process, it would be quicker to either mold/cast the second one, or make a mold and cast two. If you do not have any supplies on hand or are not familiar with the process, then building a second part would be quicker.
Is it possible to mold a cast?
Yes, this is typically called “recasting.” However, take care that you do not create a mold of another person’s work without their consent. Recasting without consent is looked down upon on the 405th, and, if caught, is an offense that could lead to a ban.
Where does molding come into the whole Pep/Resin/Bondo process?
It does not necessarily need to come into the process of building a piece of armor. Molding a piece is only needed if you intend to create copies of your work.
How do I mold a weapon; like a Reach Magnum?
After building the base gun, use a similar method to create a mold as done in this video…
I’ve seen molds that are in two parts; how do I do that?
See the question above for the process.
How much material will I need to make a mold of XX piece?
Up for a little math?
Instead of buying XX product, could I just use YY product to make a mold?
We always encourage experimentation (and share your results), but the methods and materials laid out by other members are tried and true methods with a high success rate. So, while it may be possible to use cheaper materials for mold-making, the quality/longevity may not meet your expectations.
Can I buy a mold anywhere?
Not likely. People who invest the time and money to make a mold rarely sell them.
Can I mold a master that is made from clay?
I’ve seen pictures of a helmet being cast; I know that you cover the entire helmet with the rubber mold, but what is that hard shell that people put over top of the rubber? What is it made from?
That is typically called a “mother mold.” Its purpose is to keep the rubber mold in shape during the casting process. It is typically made from strips of resin-soaked fiberglass, and may be coated with bondo to give it added strength.
How long do I need to wait before I can separate the mother mold from the rubber mold?
Once the mother mold is cured, it can be removed.
I’ve heard the term, but what are registration keys?
Registration keys are "notches" in a two-part mold that allows you to line up your mold pieces together when you are laying up your fiberglass/liquid plastic/resin.
How long will a mold last; how many copies of a piece can I make before it starts to degrade?
It depends on how thick you’ve made the mold, what quality of the rubber/silicone you used, how you handle it, how you store it, etc. There are a lot of factors to consider and no real solid answer. The better you made the mold and the better you take care of it, the longer it will last.
Smooth-On has a basic guide for their products…
Can I use a finished piece (pepped, resined/glassed, bonded and painted) to make a mold without damaging the finish?
It depends on how well the piece is finished and how well the primer/paint adhered to the piece; but it is possible.
Is there anything I should do to the mold before I start to pour a cast?
Beyond making sure the mold is clean, the most important step is to apply a release agent. A release agent will allow the mold to separate from the casting once the cast hardens. Without a release agent, the mold and casting could fuse together, and you’ll have wasted a ton of money and time.
Can I cast a helmet using Rondo?
You can. However, Rondo is heavy and, by itself, very brittle. Method would be to slush a thin batch of rondo as a first coat; then slush a second batch with fiberglass strands added to the mix. The fiberglass will give the rondo a bit of strength.
How well to casted parts take to sanding?
Depending on the material you use to cast, usually, very well. In fact, casts often need a bit of sanding/touch ups to remove seams or slight imperfections.
My cast has a ton of tiny bubbles in it; how do I avoid that?
Some casting resins work best if they are degassed once they are mixed (degassing involves putting the resin into a vacuum chamber to remove any air trapped in the resin during the mixing process). Before deciding which resin to use, read up on it and see if it requires degassing.
Does the cast have to be white?
There are pigments and additives offered by many companies that allow you to tint the color of your resin. There are even additives available if you want your cast to come out looking like metal.
I notice that there are some voids in the cast; how do I patch those holes?
The same way you’d patch a hole in a Pepakura model. Add a bit of bondo or spot putty.
Can I us a clear casting resin to cast a specially shaped visor, like an ODST visor?
You can try, but in order to get the casting resin smooth enough so you could effectively see through would be extremely problematic. Vacuum-forming is the best method for this.