Making Bo-Katan Part 1: 3D Printed Matrix Molds

We have received a lot of questions about how we make and finish our helmets, specifically how we did the 3D printed shell for our mold. Part one will cover everything from the 3D printed shell to having a fully finished mold. Part two will cover fully finishing a raw resin kit!

To start with, we want to give a sincere thanks and shout out to Sean Fields of Project 842 whose base Bo-katan models we used to create our helmets. You can purchase his models at his shop if you want to print your own! That being said, even when we start with a licensed file, we typically tend to make at least a few modifications – either for screen accuracy, to make molding and casting easier, or some combination of both and this helmet was no exception.

We made three main changes to the model after first printing. We modeled our own version of the rangefinder and stalk (not pictured) and the more significant change we made was to modify the lower part of the earcaps. To do this, we used our rotary tool to chop off the existing ones on the print, and then modeled our own to fit the existing helmet and top ear cap pieces. Once we were happy with them, we set to work on the fun (long, arduous) process of sanding, filling, and smoothing out parts to prep them for molding.

And this was where the desire to try something new stepped in. Like many folks, we’re often short on time, but doing something faster, does not always mean better; however, we are always keen to find ways to improve efficiency of process to get the same results with less effort (which tends to equate to faster). So we had the, potentially, brilliant idea to do a 3D printed shell for this helmet so we could pour the mold versus doing the brush on layered technique we did on our Armorer helmet (you can read up on and watch our video series detailing that whole process here).

Before going into detail on the specific process for our helmet, we wanted to cover the basics on why this can be a valuable, efficient tool for any mold.

1. A cavity pour mold itself will always be faster than a brush on mold for no other reason than you can pour the mold once and wait the cure time versus having to brush on and wait between layers.
2. Pouring the silicone once is also less labor than brushing on multiple coats.
3. With a 3D printed shell, the shell itself can be created by our robot minions while we work on other things (like finishing the master). We’re always looking at ways to do more parallel versus serial work.
4. When modeling the shell, we can calculate the exact volume of silicone needed to fill the cavity between shell and master, potentially reducing wasted materials (or ensuring you don’t run out before finishing!)
5. If you are doing a large production run and need multiple molds, a 3D printed shell makes it much easier and faster to produce several copies, potentially all at the same time if you have enough printers!

Granted there are some cons and potential pitfalls to this method versus the traditional way, and we definitely experienced some of them and learned some lessons – all of which we will cover as we go through our process below. And hopefully we can save you a headache or two if you choose to try a mold like this.

Step one was to plan the shell and mold before ever even touching Fusion 360. We did a few sketchea of the general idea to figure out how many parts we wanted to make the shell on and approximate where we’d put registration keys, pour spouts, etc.

We then printed a 1/6th scale version of the helmet and the initial rough shell model just as a very basic proof of concept and everything looked very promising! (Thanks to Sabine for stepping in to help with testing).

With our design and prototype squared away, we then flushed out the specific details. The way we modeled the shell was to actually model the silicone around the helmet model first! We ensured a uniform thickness all around the helmet, added registration keys and bars, and air vents (to ensure air could get out while we were pouring the silicone).

Once the silicone was modeled we then modeled the shell as a solid, paying attention only to the outside size and shape as we then subtracted the silicone model from the shell model, creating all of the vent holes and registration indentations that would be filled with silicone during pouring.

The final step of modeling the shell was to cut it into three pieces – left, right, and bottom – and to add the flanges and bolt holes for putting them all together for making the mold (and later holding the mold while casting).

With the model complete, the files went off to our robot minions to print while work on the master continued.

We aren’t going to cover this part of the process in detail as there are hundreds of tutorials and videos about finishing 3D prints, but rest assured there was a lot of sanding, filling, priming, etc. to get the helmet master ready for final painting and molding.

Because the shell is so large, we did have to split it up into multiple pieces to fit on our printer, but that wasn’t a big deal since the shell didn’t need to be perfectly smooth, especially on the outside. Here are all the shell pieces, mostly assembled. The one thing not shown here is that the inside of the shell was coated with XTC-3D to smooth it out and prevent the silicone from locking into the print lines. And now we run into our first big hiccup in this process…

While the shell was printing, we had the bright idea to modify the master! We decided to further modify the earcaps so that one base helmet could be used for either Bo-Katan or Koska with as little work as possible. This meant splitting the Bo-Katan upper earcap from what would be the continuation of the lower earcap as well as modeling a Koska upper earcap to fit the helmet. Great, no problem, right? Well, except the part where the new earcaps now did not fit inside of the shell we’d just finished printing and prepping! Yes, while it may seem very obvious in hindsight, changing your master after you’ve modeled and printed your shell, can defeat a large part of the purpose. Thankfully because this change was small, we modified our shell model, then sliced off and printed just the part that needed to be changed. We cut into the shell, glued on the extended parts over the earcaps, and resealed that part of the inside of the shell.

With a finished, and properly fitting shell and a master worthy of molding, the final steps of preparation were upon us. Because the model files include a visor template, we printed it out and glued it into our helmet to seal up the visor cut-out area while also making a nice clean spot for cutting out the resin casts later. We also glued a bottom lip piece we modeled inside the bottom edge of the helmet to make a resin catcher around the bottom of our helmet – a lesson learned from our Armorer helmet – to ensure a nice even bottom edge. Lastly, we glued the helmet, via that bottom lip, to the bottom piece of our 3D printed shell. The master was ready to go!

One of the things to keep in mine with a cavity pour mold like this, is that your shell needs to seal up so that silicone does not leak out while its being poured in. We decided to use our plastalina clay (the stuff we normally use for claying up masters for molding). Our first step is always to make ‘clay bacon!’ This just means putting the clay through our pasta maker to get a pile of thin sheets of clay. In this case, we cut strips off of those sheets and put them around the edges of where the sides and bottom of the shell would touch. The clay is only about a millimeter thick, but plenty to seal it up once we screwed everything closed. We also hot glued straws into all of our vent holes. This allows for silicone to flow up and out and force out the air bubbles without immediately spilling everywhere. Once the silicone level in the straws is above the level of the silicone inside the shell, they can be capped off (otherwise the silicone WILL pour out of them as gravity keeps pushing down the silicone being poured in). The final step before mixing silicone was to spray the master and the inside of the shell with mold release. Don’t forget your mold release!

With the master and shell all ready to go, because of the amount of silicone we’d be pouring and due to all of the undercuts and potential places for air bubbles to form against the master, we decided to start with a brush on beauty coat just as you’d do with the traditional brush on method. Once that was brushed on and tacky, we closed up the shell and then started the process of filling the entire thing with silicone. We used TC-5024 from BJB Enterprises. It’s a tin cure silicone that we use for almost all of our molds.

After pouring ALL the silicone, it was time to cross our fingers and wait for Schrödinger’s mold. The next morning, we removed all of the screws, cracked open the shell, and voila – a helmet mold was born!

We put up a quick video that shows a speed run of the silicone part of the above process as well!

But wait! Not all was perfect or well, and here’s where we come to the failures and lessons learned. We had a couple of spots where the shell was not sealed as well as it could be and silicone leaked into the shell. It would be an understatement to say that getting the shell off was difficult do to this and resulted in the master taking some damage as well (mostly just this ear cap getting broken – an easy enough fix if we ever needed to remold it – oh no, foreshadowing!) We also had a harder than expected time getting the silicone to get into the shell. We realized we should both have used a silicone thinner to help the silicone flow better as well as having more air vents. Both great lessons for next time.

While our first pull from the mold was virtually perfect, we quickly realized another issue. While the bottom lip idea worked pretty much as planned to give the bottom helmet edge a nice uniform thickness, because the lip we glued into the master was not very thick, at some point the weight of the silicone had actually partially dislodged it and so the bottom lip of silicone was very thin along the back edge. Not the end of the world as the only part of the cast that was uneven and thin gets trimmed off anyway, but we saw it as a weak point that would not last long.

After the first cast, and standing the mold upside down in a box between layers, we realized we could very quickly and easily model and print a stand for the shell! By the time our next helmet was done, we had a nice little stand that popped on and off of the shell while adding very little weight.

Remember that earlier foreshadowing? Well, after the first handful of pulls, the bottom silicone lip tore just as we’d expected. Still not a deal breaker because casting worked fine, it just meant more trimming the bottom edge of the casts before they were in a condition we’d send them out. However, we knew it would be a matter of time before that torn edge worked its way into a critical part of the mold and the whole thing failed. While it was very discouraging to have a mold that we spent so much time and effort on failing, we decided to take all the lessons learned and make a new mold sooner rather than later!

Fast forward to a newly modified and printed 3D shell – this time with the earcap adjustments baked in from the go along with more air vents and a couple of extra registration keys. We also repaired the master while the new shell was printing (and yes, we painted the fixed master orange instead of blue – doesn’t everyone have paint in their company colors on hand?) We also made a new bottom lip for attaching the master to the shell base that was double the original thickness and with a wider attachment footprint.

Bam! And there we had a brand new mold and shell and a perfect resin cast. While the casts from the new mold that we send out the door are identical to the ones we sent from the first mold, the bottom edge is a lot cleaner and casting and demolding is much easier on us. The new mold will also last a lot longer (and already has survived more pulls than the first mold).

And that’s the whole story! Want to get one of our resin kits or a fully finished helmet? Check out our shop! Hopefully we answered any questions about our process, but if we missed something, feel free to ask below in the comments or reach out to us on any of our social media!

Coming soon – Making Bo-Katan Part 2 : Finishing a resin cast helmet.