When buying a new lock for your front door, smart people consider buying a lock with a turning knob on the inside, like this:

Photo by user BlastOButter42 on Wikipedia

It allows you to lock – not just close – your front door with a turn of the knob. Well, I didn’t, and thus I ended up with a lock where I had to put my key in whenever I wanted to lock my door.

Well, it’s never too late to fix something like this. The solution is simple: Just print a knob around a spare key. And I did. This is what it looks like:

I went with a square shape, as it’s actually easier to turn than a round one. The way I did it, is I created a rounded cube in Blender, then removed an outline of my key from the inside. I generated the gcode file, then separated it into two files – one containing the lower half, and the other containing the upper half. I printed the first file:

Then I inserted the key:

And continued printing the second half (with absolute z coordinates, the printer starts off right where it stopped before; you just have to be sure that the head is first raised to the appropriate height before moving along x and y; otherwise it might crash into the already printed part).

Here is the STL file (which obviously doesn’t work for keys of a different shape):

doorknob.stl

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