Keyslink Auto is a spring loaded version of my original Keyslink. The key fires out from the front when the button is pressed and is retracted manually. You will need some springs which you can get in a small kit or individually or from other devices, as well as a couple of machine screws and nuts.The key modification is the same from the previous keyslink version, only the back is ground to be more flush with the height of the key (you can tweak it accordingly to fit into the carriage). Here is a video of it in action https://youtu.be/vNWh6GCM_as (if the video doesn't work let me know).

Doesn't Matter

Doesn't Matter

60 - 90 gives good solid construction

Orient the parts to print without supports. Assemble the parts according to the picture (the tiny carriage slot is super-glued into the bottom of the carriage to lock in the key) and drill in the spots where there is solid infill, then screw them together. You can also glue them together (a little more messy) with epoxy.