Take, for instance, the PanOceania Indigo SpecOps model for Infinity. This is one of the first models that they've ever released that encourages conversion. It comes with two heads, one with a beret, and one with a six-optic helmet. It also has a multi-rifle, a heavy machine-gun, and a spitfire in addition to the combi-rifle in the model's hand.
Here's where the problem comes in. In the rules, a SpecOps mini can be armed with multiple weapons. But the basic weapon of all of the units from which Indigos are drawn is the combi-rifle, so the only bit that includes the arm is the combi-rifle. All the other weapons are modelled without the arm, so they can be attached to the model's back, or wherever.
I don't fancy the idea of a pile of additional weapons on my Indigo's back or base. What I'd most like is to have each weapon modelled with an arm, so that I can magnetize each one and swap out arms as necessary.
Sculpting the arms from scratch would be one answer, but that's a little beyond my abilities. Instead, I've decided to make a mold of the arm with the combi-rifle, so that I can cast it and cut out the rifle and replace it with the other weapons.
The first step is to make a box. I've cheerfully accepted Bruce Hirst's customer's suggestion of using Legos for this purpose, as you can see here.
Then you fill the bottom of the box with modeling clay. I try to fill it as close to halfway as possible; this will let me use the height of the Lego box as a guide to the size of the eventual mold. When the clay is ready, you press the piece you wish to mold into the clay. Try to ensure that the bit is halfway submerged, and that the clay forms a tight seal around the edge of the piece. If there are any gaps around the edge of the bit, the liquid rubber is likely to flow down into them.
In this picture you can see three more important features of the mold-making process. First, the round depressions made by the end of a paint brush handle will form registration keys. These keys will be reproduced on both sides of the mold, and will force it to line up, helping to prevent miscasts and off-set flash around the edge of the model.
Second, I've made a little pipe of clay running from the edge of the box down to the tip of the gun barrel. This will help to form a vent for the air to escape. If the void the resin fills forms a simple depression, then even a low-viscosity resin will find it hard to flow around all the bubbles that can form. However, if there are vents that the air can flow out of, then the resin will be much more likely to penetrate every nook and cranny, doing a much better job of preserving detail.
Third, in that photo you can see a shiny finish on the clay around the outside of the bit. That is a mold-release compound. The silicone rubber that I'm using cures (hardens) in the presence of tin, which can be a problem when making a mold of a metal piece made primarily of tin. In the first mold I attempted, the rubber cured to the surface of the bit, and I wasn't able to free the piece from the mold. I ended up having to cut the bit out and scrape the rubber off its surface. The mold release forms a barrier between the rubber and the surface of the bit so that they come apart easily.
At this point, you can mix up the first batch of rubber. It goes slowly over the top of the clay, filling in all of the details. The cure time of the rubber I'm using is six hours (your mileage will of course vary); I then went to bed.
In the morning, I broke up the Legos to reveal a block of half silicone rubber, half clay. The halves separated easily, revealing the bit still stuck in the clay. I freed it, cleaning the remnants of clay from it, and then turned to the rubber.
Just like the clay served as a support form for the silicone that became the first half of our mold, the first half will now support the second. I re-made the box, and placed the rubber face up in it. I then painted a layer of mold release into the impression of the bit, and pressed the bit into it. This wet mold release will help to form a seal around the bit, again preventing the wet rubber from soaking into crevices. Then, I painted three coats of mold release across the face of the mold, waiting for each to dry before painting the next. Silicone bonds very well to itself; the mold release is necessary to enable you to break the mold into two pieces again instead of entombing the bit forever in a solid if wiggly block of rubber.
After the mold release is dry, mix up the next batch and pour it slowly over the top of the mold, filling up the top half. Another six hours, and you'll have something like this:
I say "something," because in the right half you can see a negative impression of the "pipe of clay" I made earlier. The left side will have a positive impression that fills up and blocks the vent. With a hobby knife, I shaved off the positive impression, leaving the channel open when the two halves meet. It is also possible to make the mold without vents or channels, but then you'll likely have to cut them into the surface of the mold with a hobby knife.
Here is the result of the process: two casts of the arm (with the extra resin from the vent removed), ready to have the combi-rifle removed to make way for an alternative weapon choice. I've been thinking heavy machine-gun, at least initially. We'll see!
The first step is to make a box. I've cheerfully accepted Bruce Hirst's customer's suggestion of using Legos for this purpose, as you can see here.
Then you fill the bottom of the box with modeling clay. I try to fill it as close to halfway as possible; this will let me use the height of the Lego box as a guide to the size of the eventual mold. When the clay is ready, you press the piece you wish to mold into the clay. Try to ensure that the bit is halfway submerged, and that the clay forms a tight seal around the edge of the piece. If there are any gaps around the edge of the bit, the liquid rubber is likely to flow down into them.
In this picture you can see three more important features of the mold-making process. First, the round depressions made by the end of a paint brush handle will form registration keys. These keys will be reproduced on both sides of the mold, and will force it to line up, helping to prevent miscasts and off-set flash around the edge of the model.
Second, I've made a little pipe of clay running from the edge of the box down to the tip of the gun barrel. This will help to form a vent for the air to escape. If the void the resin fills forms a simple depression, then even a low-viscosity resin will find it hard to flow around all the bubbles that can form. However, if there are vents that the air can flow out of, then the resin will be much more likely to penetrate every nook and cranny, doing a much better job of preserving detail.
Third, in that photo you can see a shiny finish on the clay around the outside of the bit. That is a mold-release compound. The silicone rubber that I'm using cures (hardens) in the presence of tin, which can be a problem when making a mold of a metal piece made primarily of tin. In the first mold I attempted, the rubber cured to the surface of the bit, and I wasn't able to free the piece from the mold. I ended up having to cut the bit out and scrape the rubber off its surface. The mold release forms a barrier between the rubber and the surface of the bit so that they come apart easily.
At this point, you can mix up the first batch of rubber. It goes slowly over the top of the clay, filling in all of the details. The cure time of the rubber I'm using is six hours (your mileage will of course vary); I then went to bed.
In the morning, I broke up the Legos to reveal a block of half silicone rubber, half clay. The halves separated easily, revealing the bit still stuck in the clay. I freed it, cleaning the remnants of clay from it, and then turned to the rubber.
Just like the clay served as a support form for the silicone that became the first half of our mold, the first half will now support the second. I re-made the box, and placed the rubber face up in it. I then painted a layer of mold release into the impression of the bit, and pressed the bit into it. This wet mold release will help to form a seal around the bit, again preventing the wet rubber from soaking into crevices. Then, I painted three coats of mold release across the face of the mold, waiting for each to dry before painting the next. Silicone bonds very well to itself; the mold release is necessary to enable you to break the mold into two pieces again instead of entombing the bit forever in a solid if wiggly block of rubber.
After the mold release is dry, mix up the next batch and pour it slowly over the top of the mold, filling up the top half. Another six hours, and you'll have something like this:
I say "something," because in the right half you can see a negative impression of the "pipe of clay" I made earlier. The left side will have a positive impression that fills up and blocks the vent. With a hobby knife, I shaved off the positive impression, leaving the channel open when the two halves meet. It is also possible to make the mold without vents or channels, but then you'll likely have to cut them into the surface of the mold with a hobby knife.
Here is the result of the process: two casts of the arm (with the extra resin from the vent removed), ready to have the combi-rifle removed to make way for an alternative weapon choice. I've been thinking heavy machine-gun, at least initially. We'll see!
