The majority of non-SLA resin 3D printers, certainly at the hacker end of the market, are most certainly LCD based. The SLA kind, where a ultraviolet laser is scanner via galvanometers over the build surface, we shall consider no further in this article.
What we’re talking about are the machines that shine a bright ultraviolet light source directly through a (hopefully monochrome) LCD panel with a 2, 4 or even 8k pixel count. The LCD pixels mask off the areas of the resin that do not need to be polymerised, thus forming the layer being processed. This technique is cheap and repeatable, hence its proliferance at this end of the market.
They do suffer from a few drawbacks however. Firstly, optical convergence in the panel causes a degree of smearing at the resin interface, which reduces effective resolution somewhat. The second issue is one of thermal control – the LCD will transmit less than 5% of the incident light, so for a given exposure at the resin, the input light intensity needs to be quite high, and this loss in the LCD results in significant internal heating and a need for active cooling. Finally, the heating in the LCD combined with intense UV radiation degrades the LCD over time, making the LCD itself a consumable item.
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The ability to duplicate keys with a 3D printer is certainly nothing new, but so far we’ve only seen the technique used against relatively low hanging fruit. It’s one thing to print a key that will open a $15 Kwikset deadbolt from the hardware store or a TSA-approved “lock” that’s little more than a toy, but a high-security key is another story. The geometry of these keys is far more complex, making them too challenging to duplicate on a consumer-level printer. Or at least, you’d think so.
Inspired by previous printed keys, [Tiernan] wanted to see if the techniques could be refined for use against high security Abloy Protec locks, which are noted for their resistance to traditional physical attacks such as picking. The resulting STLs are, unsurprisingly, beyond the capabilities of your average desktop FDM printer. But with a sub-$300 USD Anycubic Photon DLP printer, it’s now possible to circumvent these highly regarded locks non-destructively.
Of course, these keys are far too intricate to duplicate from a single picture, so you’ll need to have the physical key in hand and decode it manually. [Tiernan] wisely leaves that step of the process out, so anyone looking to use this project will need to have a good working knowledge of the Abloy Protec system. Hopefully this keeps bad actors from doing anything too nefarious with this research.
Once you have the decoded values for the key you want to duplicate, you just need to provide them to the OpenSCAD library [Tiernan] has developed and print the resulting STL on your sufficiently high-resolution printer. Generally speaking, the parts produced by resin-based printing have a high tensile strength but are very brittle, so perhaps not the kind of thing you want to stick in your expensive Abloy lock. That said, there are some “Tough Resin” formulations available now which produce parts that are at least as strong as those made with thermoplastics. So while the printed keys might not be strong enough for daily use, they’ll certainly work in a pinch.