This article will discuss the ins and
outs of one method to duplicate an articulated limb through molding and
casting, and retain the functionality of the hinge joint. This is
a technique that was first discussed by the customizer Skyflight, and I
have attempted to flesh out that technique and illustrate it here.
It should be noted that this technique
involves quite a bit of labor and materials, and is therefore a little
impractical if you only need a single joint for a project. If you
only need one joint to transplant into a custom, I would just recommend
finding a donor figure and using its joint.
That being said, there are
uses for casting your own articulated limbs. For this article, I
will be duplicating a hinge-joint arm from a 7" DC Direct Amazo figure.
In this instance, there are several reasons that justify the work involved.
First, the Amazo figure is about $18 in any store, so the math works out
that it's cheaper to make my own copies. Second, the DCD Amazo has
arms that are very generic, in that they are bare with the exception of
the wristbands, and their size and plain pose means they would work for
many 6-7" customs. Third, the elbow joints are of a good size, so
they could be transplanted into many larger 6" or smaller 7" figures.
Finally, it is not within the scope
of this article to discuss the finer points of molding and casting in general.
It assumes that the reader is already familiar with the techniques involved
in creating a two-part silicone mold and casting a duplicate with liquid
plastic casting resin. If you are not yet familiar with this process,
there are many good articles already on the web that cover the topic.
So, without further ado:
Step 1: Start with the articulated limb you would like to duplicate.
Remove it from the figure torso by your method of choice, either cracking
the torso or boiling and popping the limb out.
Step 2: Close the hinge joint as far as it will go. Using an
X-acto knife, carefully slice the inner loop of plastic that covers the
hinge pin. I try to make the incision as close as possible to 180-degrees
away from the base of the loop. By doing this, when the joint is
reattached the seam will be hidden within the joint, and will therefore
not be visible.
Step 3: Carefully pry the cut loop of plastic around the hinge pin,
separating the two parts of the limb. Most limb plastics are fairly
soft and the piece should separate without too much trouble. If it
seems like it doesn't want to give, or if it feels like it's going to crack,
place the limb in a pot of boiling water for about 30 seconds, to soften
the plastic, and try again. Continue until the pieces come apart.
Once they are separated, use superglue to repair the seam you cut in the
loop of plastic.
Step 4: Using the rubber molding compound of your choice, create
a separate two-part mold of each half of your limb. Many figure limbs,
especially in the hands, have severe undercuts. To prolong the life
of your mold, I suggest carefully inspecting each individual piece and
locating the seams from the original factory mold. Use this as a
guide to demarcate where the two halves of your mold will meet. This
will help lower the chances that your mold will tear when you remove a
fully-cured casting.
Step 5: Once your molds are ready, create a casting of the limb half
that does
not contain the hinge pin. In other words,
you are casting the limb half that contains the plastic loop you sliced
in Step 2. Once it has cured, set this piece aside.
Step 6: Next, create a casting of the other half of the limb; the
half that does contain the hinge pin. Once it has cured,
remove it from the mold. Using a Dremel, carefully grind out a part
of the section of the limb that houses the hinge pin, so that one end of
the hinge pin is free and exposed. I find the easiest attachment
to use for this is a Separating Disk in your Dremel, which lets you create
a nice, clean separation line.
Step 7: Now turn the cut section of the limb towards you. Using
a small drill bit attachment in your Dremel, drill 2 or 3 registration
holes into the cut surface, 1-1.5 mm deep. I also like to CAREFULLY
drill a registration hole into the direct center of the hinge pin.
Make sure the drill bit is small enough that you don't just obliterate
part of the pin; you want to leave a definite wall around the hole you
drill. Try to drill the holes straight down; if the holes are not
all more or less parallel, you could run into trouble later. Finally,
make sure all the holes are oriented in the same direction. In other
words, don't drill any holes into the other cut surface.
Step 8: Clean any dust/plastic pieces away from the prepared limb.
Put a good layer of mold release on all surfaces of the limb casting you've
just prepared, making sure to get mold release down into each of the registration
holes you just drilled. Place the prepared limb back into the silicone
mold. Put the two halves of the mold back together, and refill the
empty space with a fresh batch of casting resin.
Step 9: Once the new resin is cured, remove the casting from the
mold. Please ignore the terrible casting void I've created in the
new section of the limb! ;) It looks like a new, complete limb.
However...
Step 10: Because a layer of mold release was placed on the original
section, the new portion of resin did not bond to the first piece.
Carefully pry the new section out of the original. Using a carving
instrument, carefully remove any plastic flash that is around your casting.
Note in this picture that the second portion of resin filled the three
registration holes drilled in Step 7, and created three small pegs.
Step 11: Articulate the prepared section of limb with the other limb
half that was set aside in Step 5. This is done by lining the hinge
pin up with the hole in the plastic loop of the other limb half, and pressing
them together.
Step 12: Now, place the other small piece into the prepared section,
lining the small pegs up with the registration holes. Superglue this
piece on, making sure you don't get any glue on the upper half of the limb,
or its plastic loop. Hold the small piece tightly down until the
superglue sets. If you hold the piece down securely, the seam should
be virtually invisible.
Final: Once this is done, you will have a complete duplicate of the
original arm. Because it was molded and cast in such a way that the
hinge pin and plastic loop were each duplicated separately, you also have
a functional hinge joint. (Ugh!....please continue ignoring that
horrible casting void!) At this point, you can attach the appropriate
shoulder peg and use this arm in a different torso. Or if you're
so inclined, you can cut away the upper and lower portion of the arm leaving
just the functioning hinge joint itself, and transplant this joint into
a different figure's limb.