A question came up as to whether or not a 3d printed key could be used in a real lock and this is my first try at answering that question. As demonstrated in the second photo it does actually work the lock (and was used multiple times) though I wouldn't count on it lasting long. It flexes considerably due to the spring tension. Quite a bit hinges on how much torque is needed to be applied to work the lock, but it certainly can work.

Out of an excess of caution I printed this at 0.10mm using 100% fill to maximize strength. And forgot that the design got flipped: this should be printed so that the blade is touching the build plate.

Of course, this key only works a matching lock. The process I used to make it was:

• Scanned key (though a picture would work as well)
• Imported image as background into modeler
• Outlined image with a line
• Measured key dimension and scaled object to match
• Added thickness
• Measured and added key channels

The print has some significant variation from the model. If the key hadn't work I would've tweaked the model to fit the printer and filament, but (at least for this lock) it was not necessary.