I have made several props from the Locke & Key comics before, and here's another one! This one is a full scale replica of the Chain Key. In the comics, it's a 90 cm long key and opens the Great Lock, wich grants access to the catacombs below Keyhouse. In the Netflix series, it's a small key, and the Great Lock is a padlock that launches a chain and can be used to restrain someone.
3D model
I made this key with my 3D printer. Of course, it couldn't be printed in one piece, it's way too big for that, and besides, a chain isn't exactly easy to print on an FDM printer. I used a reference picture for getting the correct measurements, and then broke the key down into different parts for easy printing.
When making the 3D models, there was one thing I kept in mind: I wanted to avoid supports as much as possible. Supported areas always look ugly and require a lot of post processing to look good. For this model, however, I couldn't avoid it entirely, but as you'll see, the supported area won't even be visible.
The most important part, obviously, are the chain links. I couldn't print a full chain link, because then it would be impossible to link them together, so I cut it in half. On the inside of the rounded end, I made a cutout where the links can be glued together. This is the only area where support will be needed, and it won't be visible when the links are glued together. For additional strength, I made holes in the ends that will be connected, for inserting pegs.
On the small replica I made a while ago, these pegs were pieces of filament. Needless to say, it wasn't very strong! I had glued everything together, but the key was still quite fragile. I didn't have to ship it, the client picked it up in person, so this wasn't a real problem then. For this full size replica, the pegs are printed rectangular pegs, so it will be a lot stronger!
The ends of the key were pretty simple shapes, and easy to model. The only part that was a bit more challenging was the ring at the end. The final link of the chain needs to go through it, so there needed to be a hole for the link in it. I decided the easiest way to do this was cutting the ring in half, and then glue the parts together.
Printing and assembling
With everything modeled, it was time to start printing! It was quite a lot to print, <nr> parts in total! The total printing time, estimated by Prusaslicer, was about 100 hours, and it would use about 1 kilogram of filament. For material, I used ABS. It's easier to sand than PLA, and especially the links would need quite a bit of sanding. Another big advantage is that it can be solvent welded with PVC cement for plumbing. I used 3 perimeters, 150 micron layer height, and a 25% infill.
I printed two links (four link halves) and the two pegs to link them together in one print job. I don't usually fill up my entire build plate, if the print fails for some reason I won't have wasted as much material. Each link was sanded with 120 grit sandpaper to remove the layer lines a bit, and then the links were connected. Because of the square pegs, they automatically align correctly.
Same for the ends of the key, the parts were mostly printed one by one, sanded and then put together. Sanding is a lot easier before assembly, because it's easier to reach most spots.
And then finally, all links were connected to form a chain. At one end, the ring was glued on, and at the other end, the key bit and the ball were glued on. A bit more sanding was required to clean up the seams between the link halves, and where needed, a bit of spot putty was used.
Painting
Painting started with a coat of filler primer. I can't say I'm too happy with this stuff, though. It doesn't do a very good job filling up the layer lines. It sand quite well, though, but you need to apply a few coats, and sand in between them. In the future, I plan to try out a two component filler primer. Many people use this and report excellent results; the downside is that you need a spray gun to apply it. Since I still had a few rattle cans of filler primer, I used this stuff.
As you may notice on the pictures, I had already primed most of the parts before assembly, since it would be a lot easier to sand them. So, it basically went in this order: prime, sand, prime, sand again, assemble, fill seams, sand some more, another coat of primer, aaaaand more sanding. Oh, and in case you were wondering, yes, that's a shower curtain. When we moved out of our apartment, I kept it for this exact reason!
So, yeah, it required quite a bit of preparation. When I was satisfied with the surface, I applied a final coat of primer. This wasn't a filler primer, but a general purpose gray spray primer. The filler primer isn't suitable for painting directly, you need to apply another coat of regular primer. After the final inspection, it was time for the actual paint!
The client wanted a bronze finish, so I started with a brown basecoat. There were lots of hard to reach spots, and I had to use several passes to coat everything. It's always better to use more thin coats, to avoid drips. Luckily, the paint dried quite fast. Using a fan also helps to make the paint dry faster.
After the brown basecoat, I sprayed on a coat of bronze paint. It covered quite well, and afterwards I wasn't really sure if the brown basecoat was really necessary. Ah, well, nevermind! The key looked very shiny, new and metallic at this point. A bit too new and shiny if you asked me! So I brought in my favourite stuff to make things look a little less new and shiny: oil paint! I prefer water mixable oil paint, so I don't have to mess around with smelly paint thinners that might potentially damage other paint coats.
I used dark brown and grey to apply some dirt and grime, especially in the narrow spots where the links connect. The nice thing about these oil paints is that they dry very slowly (it can take a few days for them to fully dry) and you can play around with them a lot. Even when used sparingly, it makes a huge difference!
Finished!
After drying for a few more days, the key was finished and ready for shipping to the client. It was a really fun project, probably one of the biggest prints I have done so far. Here are some pictures of the finished project!
