Scratch Builds: Tips For Molding/Casting Your Own Parts

Discussion in 'Tutorials and How Tos' started by REDLINE, Jan 28, 2008.

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    REDLINE longer days, plz? Veteran

    Dec 2, 2004
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    Tips For Molding/Casting Your Own Parts

    "The_ONE" dropped by the Radicon forums and posted this INCREDIBLE explanation about how to mold and cast YOUR OWN TF parts:


    Why would I want to mold and cast my own parts? Good question! Here are some of the things that motivated me to try it out:
    You can make multiple "chips" of Transformer pieces and try out different paint schemes on them. This let's you see all the paint schemes at the same time and you don't need to strip the part between tests.
    You may want to modify part of a Transformer. You can cast the part that you want to modify and instead of modifying the original you can modify the cast. You can try a number of different modifications. If you don't like any of the modifications then you can still use the original part.
    When sculpting your own items, like a base, you can cast the part when it is done so that you have a robust final part. Sculpey remains fairly soft and bendable even after hardened and is still too fragile to use as a final part.
    If you are sculpting your own items you can make casts at various stages so that you won't lose much work if you make a mistake or damage the fragile hardened Sculpey.
    By doing it yourself you can see how the different types of artifacts (seam lines, air bubbles, warping, etc) can occur. You can also see how long it takes and how much it costs. These things can bring a better appreciation of the reasons behind the quality and price of Hasbro/Takara Making Molds and CHANGES to a mold.
    And as if that isn't enough, it's pretty fun to do it!
    So What Are We Going To Do?
    To keep things simple I'm going to use a very simple Energon Weapon for the master part. This means that we can make a 2 part mold. Remember this article is for beginners!

    Before you start on a project like this one you need to make sure you have all of the materials that you will need. Here is what I used for this project: cardboard, tape, scissors, two plastic tubs, two craft sticks, mixing cups, 4 marbles, Vaseline, Resin Dye Experts Choice two part mold material, and Fast Setting two part resin. That's it!

    The sequence of steps to mold and cast a part is pretty simple:

    Make a box to hold your master part to be molded
    Mix and pour the mold material
    Pull the master from the mold
    Mix and pour the casting material
    Pull the cast from the mold
    Of course, the details of how to do each step can be pretty complicated. Let's not waste any more time, now we'll jump into the details!

    Make a Box
    For this project I decided to make the mold box using cardboard and tape. It's cheap, easy to work with, and does the job. When laying out the box, make sure you leave enough room around the part so that the mold will be thick enough to keep its shape. You can simply create a rectangular box that will hold your part.
    If your part is large and irregularly shaped then you may want to add some filler to take up some of the unused space. It's worth the effort to add the filler because the mold material is fairly expensive. A good tip: recycle old molds by cutting them up into parts and using them for filler.

    When your box is built you can set your part in it and move on to mixing and pouring the mold material. Since we are using a weapon, we want to make sure that the box is on a level surface so that the mold will be level when it is done and we can easily pour the casting material into it without having to worry about leveling the mold. Next you need to take blob of clay and place it in the mold box. Coat your Weapon with a fine layer of Vaseline to prevent sticking of the mold/clay materials then Press your weapon onto it gently just so the bottom is covered. This will act as a barrier for the mold to set around so your weapon is not completely sorrounded by the mold materials.

    Mix and Pour the Mold Material
    There are some really quick hardening mold materials available. These are great if you are making casts in the middle of a project or only want to cast a couple of parts. For a final part where you want to make a lot of casts you would use a different type of mold material.
    I used Experts Choice Quick N Easy A&B Low Viscosity Mold Putty in this case. It cures in 20 minutes, is good for a small number of casts, and doesn't require the use of any release agents. It is very easy to use, simply mix equal amounts of part A (black) and part B (white) in one of the plastic tubs. Stir slowly so that you don't introduce air bubbles. When the mixture turns a uniform gray you are ready to pour.

    Pour the mixture slowly and let it run into all of the cracks. It's kind of like pouring syrup on pancakes. Take your time and let it spread all over so that air won't get trapped anywhere. . This is a 2 part mold and you will need to make 2 sides to the mold. Then you just need to wait 20 minutes until the material has hardened.
    Flip The Pancake Mold
    Ok its been well over 20 minutes and you first half is now dry. It is now time to flip your mold over to complete the second half. To do this just simply flip the mold over so that the top now becomes the bottom. Gently remove the clay from the weapon and get ready to pour the second half of the mold. Again Place a fine layer of vaseline on the top of the whole mold and weapon you have just cleaned to prevent the new mold materials from sticking to the bottom half of the mold you just created.Take the 4 marbles you have and coat them in a fine layer of vaseline. Place 1 marble in each corner of the box. And repeat the pouring process to complete the mold itself.

    Pull the Master
    Since we are molding a weapon we end up with a 2 part mold that is really easy to use. Cut the tape around the edges of the box with an X-acto knife and then peel away the bottom and sides. Now you should be able to see the seam of the 2 part mold. Bend the outer parts of the mold away from the part to loosen them up. Then just bend back one side of the mold and start to work the part out of the mold. Don't bend the mold too far or the mold material may crack. Now you are ready to cast some new parts!

    Mix and Pour the Casting Material
    I used 2 part clear resin to cast my parts. This is a two part resin consiting of Curative (clear) and Isocyanate (light tan). When the two parts are mixed a chemical reaction takes place that heats the resin and causes it to cure. Thicker areas in your cast will cure more quickly because they have more material and thus generate more heat. Thin parts will cure less quickly.
    2 Part Resin is easy to use, just mix equal amounts of Curative and Isocyanate. Place resin Dye in the mixing cup Stir slowly for 30 seconds so that you don't introduce any air bubbles. Now slowly pour the mixture into the mold. Again, take your time and let it spread all over so that air will not get trapped anywhere. But don't take too long because you only have a couple of minutes before the mixture will begin to thicken. Then step back and watch it "kick"! It should get cloudy then turn white. It gets pretty hot when it kicks, so be careful.

    If you will be pouring more than one cast you might want to use two measuring cups: one for part A and one for part B. Then pour both parts into the plastic tub to mix them. Since you never mix the two parts in the measuring cups you can reuse the measuring cups over and over without having to clean them.

    Pull the Cast
    In a matter of minutes the part should be hard enough and cool enough to pull from the mold. To pull the cast follow the same method as used to remove the part. First loosen up the cast by pulling back each edge of the mold. Then bend back one side of the mold and work the part out of the mold.

    Consume Beer and Doughnuts
    And there you have it, a casting of your original part. Time to celebrate by consuming some beer and doughnuts!

    Wow that went smooth! A perfect part the first time, cool! Um, er, well, maybe I edited things up so that it would be easy to read. I did have a couple of problems.
    The first problem was I didn't have enough mold mixture to cover my part and fill my mold box! So I had to quickly grab some filler and try to stick it in the big gaps. Next time I'll make sure to do a better job estimating the amount that will be needed. I'll also make sure I have some filler on hand before mixing and pouring.

    Just Do It
    There are lots of uses for reproducing parts for kit builders as well as sculptors. With the great materials that are out there it is easy and fun. Molding and casting should be a skill in every modelers bag of tricks!
    Warning Warning!
    OK, kids: don't try this without an adult helping out. Both the molding and casting materials can be dangerous.

    Do not take internally. Keep out of reach of children.

    As a saftey precaution, all Por-A-Kast systems should be used in a well-ventilated area and skin and eye contact should be avoided.
    Thanks Guys!


    Once again, thanks to The_ONE for this information.


    =>More tutorials, with pics

    A bit larger-scale, but it still applies:
    =>Sci-fi prop making - even has a video!

    Another how-to process, although the end product is a bit corny:
    =>Roman forts in resi

    Hint: I googled these links by searching for "How to sculpt resin parts." The techniques for sculpting in resin carry over between toymaking and model-kit making, for the most part. The only difference is the type of resin you're using. FYI.
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