Designing a chapter Part 4. - Resin cast custom shoulderpads

Last time I showed you how to make simple open face moulds and how to cast custom made insignia with them. Now it is time something a bit more challenging. Shoulder pads and one-piece moulds.

Reading the previous post is of course by no means necessary but there are a lot of details explained there that I will not repeat.

I have to confess I’m not very good at drawing. Somehow I lack the ability to draw too well, and even if I sometimes am able to produce a neatly painted mini, I cannot dream of producing enough freehand shoulder pads in constant quality and quantity. Perhaps decals would do, but I want the key symbols white, and  unfortunately I have no access to an ALPS printer, the only thing I know to print white (offset would be overkill). So, given my discovery of laser engraving I opted to go for perhaps a more subtle solution: custom embossed shoulder pads.

The first step is the same as before, carefully cut the symbols from the rubber core. This proved rather challenging for me as the chapter symbol is in a thin circle, and it required a lot of concentration and a fresh blade to do properly.

Once the symbols are cut, I superglued them on standard issue space marine shoulderpads from the bits box. 

This is pretty straightforward, but not easy at all; the pads have a curved surface and superglue tends to stick to everywhere. Be prepared to lose some of the more delicate symbols. Luckily you can salvage the messed up shoulderpads with the help of a small piece of grade 1000 sanding paper.
As usual there is a trick that may help: I glue only the central areas of the symbols first and place them properly on the shoulderpad. Once the glue sets and the symbol is fixed in place glue the edges with a toothpick and position them. In general it pays not to use the super glue jar on small pits and  pieces. 
Anyway here you see the outcome. I'm pretty satisfied on this point.

Next I cut a thin strip of 1mm pasticard, around 1mm wide, and glue it on it a piece of balsa wood. I use Balsa because it is easy to cut with a hobby knife. This bar will serve as the excess basin for the resin.
On the top of the wooden piece fix a tin strip of plasticard, 1 mm wide ad roughly the same of length as the balsa piece and glue it on the wood, on it's side.

Now glue the shoulderpads on the strip of plasticard at even intervals . Calculate how much and what shape of LEGO basin you will need, and build it on the base. Your mould's wall should not be very thick, because it should enable you to remove the products easily.
Cut a piece of plasticard that fits exactly into the opening between the LEGO blocks, glue the balsa stick into the middle of the plasticard piece and you have just finished your master.

Place the master into the basin, and mix some latex. For one piece moulds you need good quality durable and elastic rubber, so for this purpose I always use the more expensive T-Sylox RP. Paint the surface of the shoulderpads with some latex. Be neat and make sure that every little recess is filled.

When you are certain, that there are no bubbles in the rubber on the surface of the master build up two or three levels of LEGO blocks so that the wall should be about 5mm higher than the top of the pads. After the wall is built, pour in the rest of the latex. It seems that tapping (described in the last post) alone is not good enough for shoulderpads, as the "domes" are perfect traps for larger air bubbles. This can be avoided if you take a toothpick and move it around the inside curve of all of the shouderpads. Further tapping will likely reveal an air bubble or two surfacing.
By the way it is useful to regularly blow the surface of the latex as it explodes the bubbles. Again you have to wait at least 6-8 hours before you can proceed with casting.

Above you see the mould as it comes out from the LEGO basin, only the bottom pasticard is removed. When you remove the master from the mould you'll need to use a hobby knife to cut through a thin layer of rubber between the shoulderpads and the strip of plasticard they are sitting on. It is quite easy, be neat.
Now this is how it looks like after a bit of trimming with pirated manicure scissors:

Prior casting you talc the mould similarly to the open faced ones. The difference of course is that you have to stretch open the mould and brush the inside with the powdering brush. face down tap out the

Similarly to the insignia shown earlier your shoulderpads are best cast by a syringe. Open the mould a bit, push the tube of the syringe into the openings, and inject the resin into them, and fill up the casting basin too. Tap the mould on the side and from under, and repeatedly open and close the mouth of the mold to let the bubbles out. This should give you perfect results.

It is worth leaving the pads a bit more time to cure, it makes them easier to remove and much less prone to deformation when pulled out of the mould. A little more than half an hour should do.

This is what become of it. Some are satisfying, others are not good enough, but it is not a problem, because later I will work on the pads and sand and hand-engrave them until I'm happy with the results, when all these are ready, I make the final moulds.

You can finish the shoulderpads by hand and make a new mould of them, since if you use a good quality latex and de-air it properly the new mould should be practically the same quality. These below are the first finished products, as I want to start painting tactic squads soon. I think they are rather good.

The trial painted them for fun last night to:

I'm not really satisfied with the painting of the chapter symbol, but I know now how I will do it when I start my assembly line painting.
To sum up, one piece molds are perfect for cylindrical or spherical shapes like heads or one piece torsos, as there are no mould lines. Unfortunately complex or very delicate items can not be duplicated this way. Fortunately two piece molds solve this problem, and I will do the best I can to help you to shorten the learning curve.
See also:
Designing a chapter part 3. - Resin casting your insignia