Prop Making 101, with Sarah Kaiser – Part 1

At Warhammer Fest this year, attendees could get their photos taken carrying full-size replicas of a Primaris Space Marine bolt rifle and plasma incinerator. These amazing props were built for us by Sarah Kaiser, a prop maker from the United States. We invited Sarah to tell us about the work that went into crafting them, and – as always – she did not disappoint. As some of you will know well, there’s quite a lot that goes into even simple props, and over the course of these two articles, Sarah explains her process from start to finish. Here’s what she had to say:

Sarah: Hey Warhammer Community!

I’m Sarah Kaiser, long time Warhammer 40,000 fan, illustrator of fan comic Eagle Ordinary and occasional propmaker. I recently put together a plasma incinerator and bolt rifle for Games Workshop’s Community Team, and it’s probably one of the coolest things I’ve ever been asked to do!

I’ve had the pleasure of working with the Community team before and this email, like others, found me dazed and struggling to consciousness first thing in the morning.

“Would you like to put together a couple of props for us in the next month?”

This was a complicated question. Prop work can be as simple or difficult as you make it, and a month is tight for someone with a job and some side-hustles in the mix. That said, this was literally a dream commission, so the answer was pretty simple.


What would follow was a month of late nights and early mornings, experimentation, close calls, beer bribes, and one of the most hair-raising trips through border control I’ve ever had.

Spoilers for everyone who didn’t see the shots from Warhammer Fest: things turned out alright. Here’s an account of everything it took to get those two props from reference image to execution, and from one side of the Atlantic to the other in less than 30 days.

First off, I would be remiss if I didn’t acknowledge my workshop and some of the people who gave me a hand.

Making sometimes takes a village, and my village is Artisan’s Asylum out in Somerville, MA. Thank you to Andrew Anselmo who made my wiring less terrible, patiently re-taught me prototyping basics I never picked up when I fell butt-first into microelectronics as a little girl and did the lion’s share of Arduino programming at the 11th hour. To ‘Science’ Bob Pflugfelder and Jason Kuehl, who saw my plans to transport the props in bubble wrap and cardboard, and gifted me with two excellently crafted transport boxes without me even asking. And Ted, who drafted out a stand for the plasma incinerator with me on a dusty concrete floor at 3am and had it cut out on the CNC and ready by the next day.

I’m ever so lucky to know you all, thank you.

Step 1: The Frame

Depending on how the prop will be used, you’ll want to consider different trade-offs concerning weight and durability. I didn’t know the bolt rifle and plasma incinerator would spend most of their time in the Warhammer Fest photo booth, but I did know they wouldn’t need to be carried around the con. This meant that the prop’s weight would not need to be feather-light.

In fact, if they were too light, they would feel fake or cheap to someone who was only picking it up in passing. (Think of the last time you picked up a hollow plastic-cast or toy, versus a resin- or metal-filled piece. Light feels cheaper.)

Since this job was all about feel and first impressions, I chose to fit them with an MDF core that would give them some strength and heft, without being overly cumbersome for smaller kids. These were cut on a bandsaw by hand, although in the future I may use a CNC (computer-controlled saw) instead.

Step 2: Bulking it out

That said, there is such a thing as too heavy. To bulk out the prop and give it a form to work over, I chose one of my favorite crafting materials: extruded polyurethane, also known as housing insulation foam. It’s about the same shade as Screamer Pink.

Relatively safe compared to fibreglass and Bondo, extruded polyurethane is cheap, light, and resistant to impacts. “Pink foam”, as it’s sometimes called, is easy to shape with sandpaper and a breeze to cut and plane with retractable razors. This stuff is also perfect for making custom terrain boards, and chances are you’ve played on top of pink foam before without even knowing it. I love working with the stuff.

As you can see from the shot below, I carved out the basic shape of the plasma incinerator by glueing a couple of layers of foam together and planning them to fit my frame. This will provide a structure over which I can form sturdier, nicer foam later.

Step 3: Electronics Testing

Though I list them later in the process, electronics were the first thing I shopped for and started tinkering with. I’ve learned that it’s best to start with the hardest parts first, and though the Community Team hadn’t asked for lights and sound, I wanted to surprise them. So I figured this was one of those “aim for the moon and land amidst the stars” type projects since I had a very limited amount of time and consider myself an electronics programming novice. I assumed some things simply wouldn’t make it into the build and would have to be saved for another project.

Shopping List

Arduino Mega: A tiny computer with onboard memory, inputs and outputs. A hacker’s playground.

Waveshield: Module that attaches to an Arduino to help it process and play sound.

Amp + Speakers: Makes the sound LOUDER.

An addressable APA 102 LED strip: A smart strip of LEDs that can change color and dim independently from one another.

Diffused LED Panels: For the side indicators. Basically what they use to make digit displays light up!

Various switches, sensors and buttons: Including one of those super sweet light-up ones with the hood – always wanted to use one of those.

With a month’s worth of evenings and weekends to split between electronics, making, painting and packing, I knew what was possible would be determined by my success in the first week of tinkering, so I’d have to work quickly and efficiently.

To justify the risk of investing time in any one feature, I’d quickly need to make a “proof of concept”, or test it out at an individual level to see how difficult it would be to execute in the actual prop.

For example, I strung up my LED strip and downloaded its code libraries to see if it would be simple enough for a novice like me to muck about with. If this was something that would take up more than a weekend of work, I’d need to mitigate the risk by using a solid-color LED strip instead. Way less cool, but way less work. On a time crunch like this, you can’t let yourself disappear down rabbit holes on any one feature.

Fortunately, APA102 is a pretty standard chip, and a couple hours of tinkering and some draped tissue paper later it looked pretty close to what I wanted. If it looked good here, it would look good later when integrated inside the prop.

Part of the rapid prototyping process involves eliminating as many unnecessary risks and time-sinks as possible, such as crafting a custom working trigger from scratch. Instead, I chose to use a +++REDACTED BY THE INQUISITION+++, which was inconveniently attached to the rest of itself – so I introduced it to a band saw. That got a lever switch epoxied inside of it, and after some quick testing, it was wired up and epoxied over later for a custom shape. Not the most elegant solution, but it would be durable, and it saved a buttload of time.

The battery was another challenge.

Before this, as I’d always been crafting for myself and I have a Bachelor of Arts degree, my engineering method had been to add more torque, more epoxy, and bigger batteries until something worked. Clients deserve better, so I called up some friends, did some research, and worked out the approximate watt-hours that would be required to run the hungry, hungry plasma incinerator for an entire day. (Hint: It’s a lot.)

To make it more tricky, I had to fly from the US to the UK, AND I wanted it to be effortless for the Community Team to manage. That took Lipos and specialized high-performance batteries off the table, leaving wasteful standard alkaline batteries and tedious (and easy to lose) rechargeable batteries. Then the thought struck: what about phone battery banks?

A high-performance battery bank could provide the 5 volt, 2.4 amp supply my LEDs required, output a constant, regulated voltage without the trouble of step-up/step-down converters to protect my sensors, and high-quality power banks limit maximum power draw in case of a short. Plus, simple to charge! Score! (To anyone who wants to try this, it’s important to note that most power banks also have a minimum draw and will shut off to prevent power leakage if this is not met. These numbers are hard to find online, but can be worked out with some LEDs on a breadboard on a case-by-case basis.)

But then, yet another challenge. How to determine how much power was left at any given moment without opening it up and fishing out the battery?

While I might have been able to open up the battery and bust out its LED indicators, that would ruin the Community Team’s ability to easily change the battery out should it ever have a problem, or if they acquire a backup. Monitoring the battery’s output with a current sensor and calculating remaining power was also a time sink – it would require time to set up and calibrate, and would grow inaccurate as the battery grew older.

So instead, I soldered together a line of photoresistors (which sense light) to monitor when an LED indicator was turned on. It only took a couple hours, and it worked! And as they say, if it’s stupid and it works, it ain’t stupid.

Buttons were tested and attached, LEDs were glued and wired with resistors in-line, and a super sweet light-up toggle switch with hood was screwed on (and then played with, vigorously). Though I’d chosen to use some plywood as a backboard to attach everything, I think if I’d had some more time to think on it, I would have used acrylic instead. Even after painting, the texture still seemed too obvious to me.

And soon all the variables were sorted and tested, and freakishly… everything worked. Independently. The next part would not be so easy.

Step 4: Assembling the Electronics

For an electronics novice like me, this is where things got hairy. I work with parts all the time, but to make a reliable system, you need experience, forethought, tools, and time. I only had a couple of these things, and with them, I did the best I could.

This is the part where I can tell you, for a fact, that a day of molexing your connectors and managing your cables will save you a lifetime of head and heartache. I did not have a day, but fortunately, I had luck and good labelling. This time. I learned a lot from this project, and will certainly use them next time.

Step 4B: Bolt Rifle Shenanigans

With the plasma incinerator, I knew I had a challenge, so I started early and gave myself time to order new parts if I needed to. The bolt rifle only needed sound, and I’d done sound before. I even had an amp, trigger, and speaker all wired up and ready to go, so I ordered a supposedly super simple Audio FX board from Adafruit and saved it for last. I have since learned my lesson.

The Audio FX board came dead on arrival and, discovering my simple solution had failed near the final hour, I was faced with borrowing a friend’s Arduino and wave shield instead. I was effectively using a nuclear bomb to swat a fly, as all I needed to do was pull a trigger and play a sound, but this thing would have (four times) more computing power than what went up with the first space shuttle.

As I was three weeks in, rather sleep deprived, and left with a week to finish and paint I was ready to cut my losses and leave it without sound. Andrew, my Arduino advisor, slapped some sense into me and more or less pushed it through at the last moment. I remember running around my makerspace making celebratory ‘pew pew’ sounds at around 2am on a Sunday as it finally came together.

To my complete shock, every component I had planned for had been integrated into both guns and was working. I hadn’t needed to compromise on any aspect of the electronics. I’d call it a Candlemas miracle, but in truth, it was merely many sleepless nights, a workshop full of resources, and an invaluable team of patient friends and advisors.

But that’s only part of the story!

We’ll be back next week as Sarah explains how she turned her pink foam and NASA-grade electronics into wargear fit for the Angels of Death…

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