As part of a long-term project to put together a costume from the Star Trek Online MMORPG, I've been making a set of combadges and rank pips.
Like most MMOs, Star Trek Online allows players to customize their in-game character by mixing and matching costume pieces from different eras. However, in my case I'll be sticking with the "official" 25th Century designs used in promotional materials.
The combadges are 2.5" high and 1.67" wide, with four variants:
- Plain (civilian consultants / Starfleet Intelligence)
The plain combadge is the base model upon which the department variants are derived from, so any fundamental changes to the former will automatically apply to the latter.
Both the 2409 and 2410 combadges have the same physical design, but will be rendered in different materials - brass for 2409 and aluminium for 2410.
The combadges will be affixed to a costume using two pairs of neodymium magnets, to help the wearer orient the badges on the uniform quickly and correctly without futzing around in front of a mirror.
As for the rank pips:
- The 2409 "Sierra" version are worn on the right chest, and consist of brass parallelograms 0.625" high and 0.5625" wide.
- The 2410 "Odyssey" version are worn on the right collar, and consist of aluminium bars 0.625" high and 0.3125" wide.
The pip/rank convention pretty much follows what was in TNG/DS9/VOY, with a Captain wearing four solid pips.
To turn the CAD models into actual badges and pips, a process called "Cold-Casting" is used, which is similar to regular resin casting.
There are three main stages:
- Master molds are made via CNC Milling or 3D Printing
- Negative "daughter" molds are cast from the masters with flexible RTV silicone rubber
- The final items are cast from the silicone "daughters" with a mix of polyurethane resin and metal powder, then trimmed to remove sprues and excess flashing
The "daughter" molds can be reused several times before wearing out, at which point replacements can be re-cast from the master.
For my first attempt at making master molds, I turned to 3D printing via an online 3D printing service platform, which put me in touch with a local guy with a printer.
Unfortunately, despite the guy's reassurances, the prints turned out quite poorly - many of the pins for the sprue lines snapped due to poor packaging, and the coarse texture of the prints completely obliterated the desired surface details of the items. He was also put the wrong recipient name on the parcel, and then blamed me for "changing my requirements" when I pointed out the quality issues.
In the end, the online 3D printing service ruled in my favor and gave me a full refund, so the exercise wasn't a complete loss. That being said, I will never be using that printing service again, especially not with that printing guy.
ASIDE: The print on the top right was treated with acetone vapor polishing, which did not mitigate any of the issues.
Several months after I started this project, I managed to get my hands on a Nomad 883 Pro Desktop CNC mill by Carbide 3D. This meant I could now machine higher-quality master molds myself, instead of engaging the services of a machine shop, as most local firms are not interested in small one-off jobs anyway.
Here, I'm roughing one of the combadge masters out of Renshape, a medium density polyurethane tooling board more commonly used to make fibreglass mold plugs. I invested in a small collection of various solid carbide endmills, including some micro endmills with extra long reach to get all the fine details and deep features.
The completed master molds, coated with acrylic clear gloss paint to seal the pores in the Renshape.
Closeup of the Command combadge master mold.
Closeup of the 2409 Pips master mold.
Note the smooth chamfers and radii in the pips, as well as the crisp recesses in the half-pips.
The daughter molds were made from Smooth-On Mold Star 30 RTV silicone rubber, which has a mix ratio of 1:1 A:B by volume.
Silicone mold casting in progress.
Mold Star 30 generally does not need degassing, but I would pour the mixed silicone into the mold as a very thin stream to break up any air bubbles. I also periodically sloshed the silicone around to coat the mold surface evenly.
The cured silicone rubber daughter molds.
The white spots on a few of the molds was a goof-up on my part - towards the end of a tub, I didn't mix/scrape the bottom properly. That said, they seemed to have cured properly anyway.
For my first resin casting trial, I chose to start off with the combadge backing piece.
I sprayed some Mann Ease Release 200 release agent, brushed it gently over the entire mold surface to ensure an even coat, then left it for five minutes before hitting the mold again with a second mist coat.
I'm using Smooth-On's Smooth-Cast 325, tinted with a couple of drops of So-Strong Black tint. Smooth-Cast 325 has a very short pot life (2~3 minutes), so one has to mix and pour very quickly.
A syringe helps make depositing mixed resin easier.
To improve the final strength of the casting, it needs to be post-cured around 50°F / 65°C for a few hours.
As I do not have a proper lab drying oven (and I'm not keen on using my kitchen oven, either), I cobbled together a ghetto hotbox out of a simple wooden enclosure with an old incandescent light bulb.
My first resin part!
A few minor dimples and a slight orange peel finish, but since this backing piece will be hidden inside a costume, this isn't a major issue.
Casting the 2409 and 2410 pip backing pieces.
The 2410 pip backing is a two-part mold, so I held the mold halves together with some scrap acrylic and rubber bands. In hindsight, I should probably have covered the one-part 2409 pip backing mold with a weighted polypropylene sheet to ensure a crisp flat rear surface.
Demolded combadge and pip backings, with sprues and flashing not yet removed.
For the 2409 Combadges, I'm using Smooth-On's 325 mesh brass powder. The mesh size is quite important because the powder needs to dispense properly in the resin, and fine powders would give better finishes once polished.
To further improve the surface finish, I dusted the mold with brass powder, tipping out the excess for reuse.
Working with metal powders is no laughing matter - they are classified as eye and respiratory irritants, so invest in a good pair of safety goggles and respirators with the proper dust filters.
Also, make sure to change your filter cartridges regularly as per local ordinances - in New Zealand, it is six months from when cartridge is first removed from its packaging (according to WorkSafe regulations).
In this test, I'm using a 1:1:1 volume ratio of Smooth-Cast 325 Part A : Part B : Brass Powder. I'm also adding a little So-Strong Brown tint, as some folks on the RPF claimed this would give better definition to my castings.
The trick here is to mix the metal powder with the Part B first, and allow air bubbles to come out first before adding the Part A - once the cold cast resin is fully mixed, you only have a short time before it starts to gel and become difficult to work with.
This is where I dun goofed.
Originally, I estimated the volume of resin and powder required based on the volume calculations of the mold cavity in SolidWorks, plus a little bit of tolerance for material left behind in the mixing container. While injecting the mold, however, I thought I didn't mix enough cold cast resin, and so in my panic, I declared this as a short "shot", and didn't weigh the mold down.
Around ten minutes later, the resin already in the mold started to expand a little, filling up the rest of the mold.
Demolding my first (trial) cold cast. The dull mustard-like appearance is expected, as the resin has seeped into the dusted brass powdered mold surface, which we can polish later.
Back of the trial cold cast, showing how the mold halves were pushed apart by the expanding resin.
I gently buffed the casting with some 0000 grade steel wool, followed by a rag soaked in Brasso metal polish. The metal lustre of the dusted brass powder came out, but the brown tint made the casting a shade too dark, giving it a somewhat aged brass appearance.
With this knowledge, my second attempt was far more successful, and closer to the desired appearance of the final product.
- Left: Second attempt with untinted cold cast resin
- Right: First attempt with So-Strong Brown-tinted cold cast resin
As of time of writing, I have finished all the 2409 brass badges, and halfway through the 2410 aluminium ones.
Final photos coming soon!