Learn How a Modern Door Lock Works with this 3D Printable Pin Tumbler Lock Model

A standard pin tumbler lock mechanism

The modern tumbler lock is one of the most common mechanical devices in the world, but very few people know how they really work. The design was first patented in 1848 but is derived from concepts dating back as far as 4000 BC in ancient Egypt and it remains the most common method of securing doors. The mechanism uses spring loaded pins of varying lengths that prevent the lock from opening if the correct key isn’t used. The modern key, usually flat and serrated, is cut to match the exact length of each individual pin. So when the key attempts to turn to open the lock, if each edge isn’t the exact length of each individual pin the lock mechanism will stay locked.

This design works so well that over 150 years later locks based on it have become virtually ubiquitous and will most likely still be the standard for many years to come. But as with just about any mechanical device, being secure doesn’t necessarily mean that it is unhackable. Lock picking has become somewhat of a growing hobby–not for illicit purposes, but simply for fun. Learning to pick a lock without a key is often seen by enthusiasts as a game or a puzzle to be solved, and considering the types of skills required to pick a lock it is pretty easy to see why.

This 3D printed pin tumbler lock has a cutaway so the internal mechanism can be observed

When Thingiverse user and Finland native Ceravyn first started exploring the hobby of lockpicking, she admits that it was basically inspired by her own boredom. But what initially started as a way to alleviate that boredom quickly turned into a fun, random skill that she could teach herself. Ceravyn (or Sara) told me that she has a passion for learning how things work and why they work the way that they do. She’s found that the best way to do that is to just start taking stuff apart and seeing what you find.

“Many things sound complicated at the start, are enclosed, and their action happens where you normally can’t see it. Whether the thing in question is a transmission of a car, computer hard drive, or a pin tumbler lock in your front door. You can of course search pictures of all of those things, but what that will tell you is that a transmission has a bunch of gears inside, hard drives have round discs and some sort of weird metal arm, and locks have pins and springs. But pictures can never help you understand how they work as easily as having a working model on your table that you can play with,” Sara explained.

So after building her own Prusa i3-derived 3D printer Sara decided to design and 3D print herself a working Pin Tumbler Lock mechanism, which she was kind enough to share on Thingiverse. Her 3D printed lock would include a cutaway window so the inner workings of the pin tumbler mechanism would be visible, and would be an easy way to understand exactly how it worked or it could also be used to improve anyone’s lockpicking skills. The design was initially a way for her to combine her lockpicking hobby and to improve her 3D modelling and design skills. Sara said that to date this is probably the most complex model that she’s ever created.

All of the models parts, including the plug and the housing, were 3D printed in PLA with a 0.2mm layer height using a 10% infill. Because of their size and the need for some precision, the driver pins and the key pins were printed with thinner, 0.1mm layers. She used springs that she salvaged from several clickable ballpoint pens to work the key pins. All that she needed to do was cut them in half to obtain the correct height needed for the mechanism. The model does not include a key as it is mainly for practicing lockpicking, but it should be relatively easy to 3D print your own working key; there are plenty of 3D printable key models available on Thingiverse.

While Sara is just now learning how to use her own 3D printer, she has been familiar with the technology for a few years. She first discovered 3D printers at a local maker event that was showing off some, at the time, new Mendel 3D printer technology. But it wasn’t until last summer when she found her local hackerspace community Helsinki HackLab (also a great band name by the way) that she decided to build her own printer and explore 3D design. While she had a lot of fun at first printing models that she downloaded from Thingiverse, Sara found herself wanting to use her Prusa i3 more as a learning tool, rather than just an expensive toy.

Her first major design and 3D printing project is her pin tumbler lock model and she designed it entirely in Solidworks. Previous to this design, she had no experience or formal training with 3D modelling or CAD, so using tools like YouTube tutorials and other online resources Sara completely trained herself. The final design took her about three hours to finish, and while she was very happy with the results, Sara says that she still has a lot of learning to do. Go ahead and let us know what you think of Sara’s model and what you think of lockpicking as a hobby on our 3D Printable Pin Tumbler Lock Model forum thread at 3DPB.com.