First off, here’s the end result:

The 3D model I used for this was this design from Etsy. It was well-designed, and looked like a closer match to the on-screen prop compared to the other models I saw.

Like the jetpack, I printed it in plain white PETG on my Bambu Lab P1S, then followed the same steps for sanding and painting from my previous post. (side note: the weld lines are part of the 3D model itself.) Unlike the Veepy jetpack model, this one came segmented in ways that would result in visible seams. Or at least it would with my printer — it did include a model of the whole helmet at once, if that’ll fit on your print bed.

Here’s a comparison picture between the old and new helmets, which also shows the (taped-together) sections of the new one:

To deal with the seams, I originally figured I’d use some classic Bondo auto-body-repair stuff, but at one point when I was picking up supplies, I happened upon the much more appealing plastic resin goo that cures immediately under ultraviolet light. I was an instant fan of that stuff — take your time applying it, it won’t harden until you want it to, at which point you can cure it immediately and not wait to continue working on it. It’s nice and sandable after curing, too. I used that stuff to cover up the seam lines, as well as to smooth out the top surface lines on the jetpack flaps, and even to extend part of of the central section of the jetpack that didn’t quite print perfectly.

This may have been a mistake, but I painted the top fin separately from the rest of the helmet, and then tried to glue it in place. Even after sanding the relevant spots, it was an incredibly tight fit. If I redid things, I’d try attaching it before painting.

The lenses were another tricky element. Those are tinted acrylic, thermoformed to the appropriate shape. The shape you’re using to press the hot acrylic sheet against is called the Buck. You wouldn’t want to 3D print the buck itself, because it would deform the printed plastic. The 3D model for the helmet included a model for an inverse mold of the buck, into which you can pour Plaster of Paris to make a solid buck that can survive oven temperatures.

Once the paster bucks were made for each eyepiece, I cut some pieces of 1/8″ thick tinted acrylic sheets to slightly larger than the shape I needed. I heated up an old toaster oven to 450-500F, and put in the buck with the acrylic piece on top of it, and waited a few minutes for the acrylic to visibly sag, indicating it was suitably bendy. It won’t droop enough to just flow over the buck like melted cheese — you need to force it into the shape. The best solution I found for that was to take a smooth silicone project mat and lay it over the piece, then press down hard on it with both hands. The silicone mat got warm, but not hot enough to burn me. Once the lenses were the right overall shape, I trimmed them down to the exact right shape with a dremel tool.

I wanted something to black out the mouth holes without restricting airflow, because otherwise I knew from my previous helmet that it would fog up the inside of the lenses pretty quickly. I had tried a few different solutions on the previous helmet, but eventually landed on the thing I used for this one as well: I took a black N95 mask from my COVID-days stash and cut out the outer black layer of it. It lets air through just fine, and doesn’t cause the lenses to fog up as much.

The inside of the helmet has a bunch of generic helmet padding stuck on it so it doesn’t rattle around on my head, and I made a quick fake leather chinstrap for it. I’ll be replacing the strap now that I’m starting on the leather work for the jetpack harness.

Oh, one last thing. For the first helmet, I was concerned about it being awkwardly sized, so I improvised a method of determining the proper amount to scale it in each direction such that it fit my head, but just barely. I took long LEGO plates and built a bit open rectangle and adjusted it in or out until I could just fit it over my head without issue. Then I measured that. Then I printed the single-piece version of the original helmet at about 30% scale, and measured the head opening with calipers, and scaled that up to 100%, and did the math to determine to appropriate scaling in each dimension. For the new helmet, I did the same thing, using the same LEGO frame as before. And once I printed the 30% version an scaled up its measurements, I found that its head opening was within a couple of centimeters of the target size. So no scaling needed. Fortuitous!

All of the pieces were printed using plain white PETG filament, so everything came out looking this this:

Painting anything like this was a new experience for me, so I learned a number of lessons along the way. I don’t have an airbrush, so I was going to be using regular spray paint cans, which can give a good metallic-looking finish if the surface is sufficiently prepared for them. Spraying chrome paint on the parts straight out of the printer would look awful, because the surface needs to be smooth. The shiny reflective paint will highlight every non-smooth detail on the surface, and every one of those will make it look less like metal. That means the visible layer lines from the 3D printing process have to be smoothed out, and so does any other disruption in the surface.

I went through some trial and error through the project, but in general I worked over the parts with a low-grit sandpaper (always wet sanding, to avoid making a cloud of plastic particulates), then put on a layer of sandable filler primer to help fill in the gaps, then (wet) sanded that with a medium-grit sandpaper, then repeated those two steps if it seemed necessary. Once I got things looking about as smooth as the primer would get, then I’d put down a layer of glossy black paint, and then go over that with a high-grit sandpaper. Then I’d bring out the chrome spray paint, doing lots of quick passes from slightly further away than the rest of the paint. Before any spray-painting pass, I’d wipe the surface down with a microfiber cloth, then with a tack cloth to make sure the paint wouldn’t hit some errant bit of dust or lint.

Once I got this process down, the pieces started looking incredibly metallic:

This was the first piece that I successfully got a good metallic finish on, and at this point I was stoked. I always intended to make something better than the first jetpack attempt, something that would make the first one look like a toy. But at this point it became clear that I could potentially make something indistinguishable from the on-screen props, and that inspired me to put in a lot of extra effort. I think this was also the point when I decided to add electronic effects to it.

The downside of that metallic finish was that it was _fragile_. Handling it rubbed paint off on my hands, and it dinged visibly and easily. I needed to protect things, so I grabbed a can of clear-coat spray protectant from the same brand of spray paint.

This was a mistake. Do not do this.

This was one of the first big lessons I learned here: I guess the clear-coat spray paint can be used successfully over regular colors, but using it on top of metallic paints just ruined the finish. I eventually found an explanation: the metallic spray paints are basically clear paints with tiny metallic-looking particles suspended in them, and when you spray it on something, the metallic particles stick to and coat the surface that you’re painting from inside that suspension, which is why it needs to be that smooth. But if you then spray the clear coat on it, it uses the same solvent as the metallic paint, so it just loosens up all of the metallic particles and lets them float around loose in the suspension, losing the smooth shiny surface. I saw some reports that you could successfully do this, but the steps were very fiddly and seemed to rely on a lot of luck.

Trying to find what people used as an alternative was tricky, because a) lots of people who are serious about this sort of thing are using airbrushes, which have different constraints, and b) the main product that people recommended no longer exists. The product in question was Future Polish, some brand of clear floor polish. It’s gone now, but I picked up a random brand of clear floor polish, squirted some onto a paper towel, and wiped the pieces down with it, and that seems to be working out well so far. It doesn’t look quite as good as it did with just the paint, but it’s a lot more durable.

So the main body of the jetpack was all done using chrome Rust-oleum spray paint. I tried their silver option, but that had a glittery finish that didn’t look right. The nose cones are a slightly different color in the movie, and based on a tip I saw online, I used Tamiya TAM85075 spray paint for those, and it seems like a perfect match. For the helmet and fan blades, I used Rust-oleum’s “metallic champagne bronze” and it seems fine.

If this was the kind of project I did with any regularity, I’m sure I’d pick up an airbrush and it would help. But I’m happy with the output of this process.

I have long been a fan of the 1991 film The Rocketeer, and especially the iconic design of the hero’s jetpack and helmet. A few years ago, I thought “why do I even have a 3D printer if I’m not going to make a replica jetpack?” So, I found some decent free STL files and printed them out using metallic-looking “silk” PLA filament. The proper approach to something like this would involve a ton of sanding and painting to get a realistic metallic look, but I wasn’t going to commit to that kind of effort. The end result was pretty satisfying and well-received:

That’s them hanging on my office wall. I filled in various seams on them with metallic-looking hot glue that did a reasonable job imitating welding lines. The harness was pretty rudimentary, just consisting of some woven nylon straps and metal buckles.

Towards the end of that project, I found a much better-designed 3D printable model of the jetpack, but it would have required actual sanding and painting — the silk filament looks reasonably metallic at a distance, but not if you put it next to actual metal, and the better design used a number of metal components. So I purchased the improved design and filed it away for the next time I felt the need for a really obsessive project. A couple of months ago I decided it was time, and I’ve been very pleased with the results. So now it’s time to start documenting the project.