A love of making stuff is something Will and I have in common. For Fanfest 2016 I made half a dozen sets of cufflinks in the shape of Revelation dreadnoughts as gifts. Asher Kagen asked me to write up a post explaining how I did it.
Making the cufflinks is a three stage process: printing a master, making a mould, then pouring the metal.
Step 1. Making the Master
In order to make a mould, we need a master – something in the shape of the cufflink we finally want. With the advent of 3d printing this no longer requires art skills, so it’s within my reach. The first stage is to assemble a CAD model of the shape. In this case I used geometry extracted from the game client using TriExporter and imported into Autodesk Inventor. It would be easy to write a large essay on this topic alone, but for now we’ll gloss over it and perhaps I’ll write it up some other time.
Printing requires a model that is “manifold” (a watertight model where all the edges of a face meet the edge of another face) – the Eve ship models are intended for a surface renderer that doesn’t require them to be manifold and there may be a lot of cleanup required at this stage. In many cases, it may be easier to build the model from scratch than try and fix all the errors.
With the model complete, it can be exported in STL format and sent to a 3d printer. Since these masters were small and a good surface finish was important, I used an OBJET3D UV-cured resin polyjet printer.
Some 3d printing technologies are more suitable than others for this sort of application. Polyjet and SLA give good surface finishes; SLS and FDM printing are likely to give rougher surfaces that would require polishing.
The beautiful resin masters out of the printer (and before removal of the surface jelly that you get out of a polyjet printer.) Because I’m lazy, and because this was an experimental process, I only made a mould for one of them, and the cufflinks aren’t a mirrored pair.
Step 2. Making the Mould
It is possible to cast pewter in an open-backed one-piece mould, but I’ve tended not to get very good results with it. It’s better to use a closed two-piece mould even though that’s slightly more complicated to make. I used RTV-101 high temperature silicon rubber to make the mould, ordered from tiranti.co.uk because they have a shop very close to where I work. Aside from the RTV-101 and its curing agent, you will need: plastic cups, scales accurate to 0.01g, a sponge, a disposable stirrer, a small amount of Vaseline and some LEGO.
The first stage is to build a mould case. I like using LEGO for this; it’s convenient, it seals pretty well and the nodules form really good locating points between the two halves of the mould.
You want to leave about half an inch of space around the master, with maybe an inch on the side you’re going to cut the pouring channel into (in this case, the right hand side; I actually went back to remake this mould later) to give you a good long channel. A long pouring channel increases the pressure in the mould, which means the metal fills small gaps better.
Use a lump of bluetack (or plasticine) to support the master, and make sure it comes up to the outer edge. You don’t want any overhangs or it’ll make the mould hard/impossible to separate. Make sure you leave pretty much a complete row of LEGO nodules around the outside edge; they’ll serve as your locaters.
Mix your silicon rubber up in accordance with the instructions. Some handy tips I learned the hard way:
- Estimate the amount of silicon you’ll need by the length/width/depth of the mould case (up to half an inch above the top of the master) and only mix up that much. No sense in wasting silicon.
- Be really careful when measuring your quantities – this is where those 0.01g scales come in. If you get these wrong it won’t cure, and that’s a shame.
- Mix like crazy. If you don’t mix thoroughly it won’t cure. I set an alarm for two minutes and vigorously stir the whole time.
- Paint a thin layer of silicon over the bottom surface of your mould with a sponge (see below) and leave it for a minute to let bubbles pop through the surface. I’ve found this really helps give a good inner surface without air inclusions.
- Pour the rest of the silicon in slowly into one corner of the mould case and let it slowly flow over the rest of the mould. This minimises air inclusions, which remain the enemy.
Once you’ve poured the first half, there’s nothing to do but leave it overnight to cure. Resist the temptation to poke at it – give it a full day and come back. Then dismantle the mould case around it, check it’s cured, and prepare to make the second half of the mould. Don’t remove the master!
To make the second half, you want to flip the first half upside down and rebuild the mould case around it, ensuring that you have walls more than half an inch high than the top of the mould. Paint the exposed silicon of the first half with Vaseline to prevent the second half bonding to it, then repeat the mix-paint-pour process. If you’re making cufflinks, your master will have a block sticking out of the back the size of the cufflink’s bar. Make sure you don’t pour higher than the level of this block!
Once you have the two halves cured, you can separate them, remove the master and cut the pouring channel. You want this to be about half an inch wide at the top, a mm or two wide where it touches the cavity, and to touch the cavity at a place where the sprue will be easy to cut off and clean up. For the Revelation, I cut the channel so it touched the cavity at the extreme back end of the Rev.
Step 3. Pouring the Metal
THIS STAGE IS DANGEROUS.
DO YOUR RESEARCH
USE PROPER PROTECTIVE CLOTHING.
BEWARE STEAM EXPLOSION.
DO NOT DO THIS IF YOU ARE A MINOR, DRUNK, IRRESPONSIBLE OR IT’S NOT YOUR KITCHEN.
I used lead-free pewter, which has the advantage that it melts at a temperature you can reach with a kitchen gas stove. It’s still a sufficient temperature to cause yourself really severe injuries if you touch it though, so be helluva careful.
For this stage, you will need: a casting ladle and some lead-free white metal (both of which you can buy at Tiranti.co.uk) a metal baking tray to work on, some kind of clamp to hold your mould together, cufflink backs (available from eBay), talcum powder, probably a set of bolt croppers to chop the white metal ingots into comfortable sizes (and who hasn’t always wanted a reason to own bolt croppers?) pliers to handle the hot cast, safety glasses (seriously, don’t risk your eyes here) and welder’s gloves.
A kitchen gas stove is sufficient to melt pewter. Set the ladle up over a gas ring, and put a couple of chunks of pewter in it. While that’s heating up, prepare your mould. Dust the inside lightly with talcum powder, and push a cufflink back through the hole in the mould. Plug the hole with a spare bit of cured silicon.
Mate the two halves of the mould together, and clamp them. You can use a DIY clamp, or for something this small, just wrap string around the outside. Once the metal has melted in the ladle and it’s good and hot, pour it carefully into the pouring channel in the top of the mould. Be careful not to overfill, or it’ll flow down and potentially knacker the cufflink back.
Give it five minutes to cool down from “molten metal hot” to merely “burn your flesh if you touch it hot” and you can open the mould up. Take off the string and pull the two halves of the mould apart.
It’ll take a bit of work to extract the cast from the mould because of the cufflink back. Remove the silicon plug, straighten the back, and push it out carefully. Use pliers because it’s still hot enough to burn you. Leave the cast on a metal surface, reassemble the mould before it cools too much, and you can pour the next one.
With the mould extracted, all that remains to do is cut the moulding flash off using side cutters, then clean up the area with a fine file or sandpaper.
Et voila – a beautiful thing to give to any menswear-loving siege enthusuiasts you may know. (Or, y’know, may randomly accost in the Harpa.)