To test the 3D printed Facade overlay, we first created a design probe---a 3D printed sheet in PLA plastic of buttons labeled with Braille acronyms, attached to the microwave. We used an inverted cone shape for buttons, with the radius of the top surface corresponding to the actual size of the original button, and the radius of the bottom surface smaller. Thus, the design reduces the pressure required for blind users to press on the top surface to activate the original buttons on the microwave. To minimize assembly time, we attached the buttons in a grid with connectors between buttons, so that they could be batch printed, and also attached to the physical interface as a whole. We also made the connectors very thin so that the plastic buttons deform more easily when pressed. All of this design work was done by hand, but in a style that can be automatically generated for Facade.

We tested this design with the same participants from our formative study, and identified the following issues:

• Some unexpected 3D printed artifacts on the edges of the top surface made the Braille dots feel overly rough, reducing readability.
• Due to print resolution, Braille dots had different heights, reducing readability.
  
• The plastic buttons were too hard to push.
  
• The button set did not attach to the microwave panel well and fell off after several times of use, due to the small contact regions.
  
• Because PLA does not deform, the connector bridges broke after pressing for a few times.