You can add some features or extra functionality by sacrificing a button with these custom inserts. I printed these on my PrintrBot Simple Metal (which I would reccomend btw).
The first insert will house a switch. The second is a slot for US quaters. The under side of this insert has a flat area to mount a optical sensor to builld a working coin acceptor. I will add more photos of this assembly when I get more optical sensors in the mail :)
I included the STL and AutoCAD Inventor 2014 files.
The switch an opening of 0.505" x 0.805" (+/- 0.01"). The quarter insert has an opening of 0.90" x 0.095". Quarter slot is slightly oversized to accound for tolerance issues due to PLA shrinkage and different printers. I am slightly new to 3D printing; accounting for shrinkage and printer accuracy is all over the place for me.
The STL files are in milimeters (mm).
Inserts fit 1.125" button holes.