Labels are used to generate a 3D model for a tactile and pressable button layer, matching the original controls, and the users can specify settings of the printed overlay in the Facade iOS app once labeling is completed. Informed by our study, we allow individual buttons to be customized using Braille, embossed letters, or embossed symbols. This allows users to mark specific buttons with their own conventions with the VoiceOver functions on iOS. Although embossed capital letters were not mentioned in our study, blind participants did mention using shared machines at home and at work with sighted people, which embossed letters allows for co-located access. Embossed letters also improve access for non-Braille readers, who can recognize capital letters almost as well as Braille readers recognize Braille. Finally, users can customize the abbreviation strategy (i.e., which letters are used to represent a word or phrase); whether a legend is generated; which buttons are labeled or which buttons will remain flat; and the shape of buttons (useful for differentiating special buttons such as numbers).

Based on the results from our formative studies, we decide by default to detect and use different shapes for function (rectangular) and number (spherical) buttons when generating the 3D tactile overlay. Following common numeric keyboard or button pad accessibility conventions, by default we only label number 5 with a dot on the spherical button for the numbers.

The settings and the crowd-generated labels are then passed to our automated design tool. We implemented an OpenJSCAD script to generate the final STL files of 3D models of the augmented buttons for printing. The input to the program is a generated JSON object including the dimensions of the tactile overlay, average button size, as well as the dimensions, positions, labels and preferences of each button. With this data, the script first generates groups of 3D buttons with labels.

We determine the depth of the buttons to be proportional to the size of the buttons. To get the scale factor for Braille and letters, we first divided the button width by two to situate two characters, and divided each area to hold two columns and three rows of dots including spacing. Compared to the standard dot radius and spacing size, the proportion is defined by this scale factor, and applied to the size of letters and symbols.

If short acronyms are not provided for each button label, the program automatically generates the abbreviations. By default, when adding Braille on top of the buttons, we use two characters for each button due to the limited surface area and the size of Braille characters: a word (e.g., `Clock') is abbreviated by the first two letters (e.g., `CL'); and multiple words (e.g., `Power Level') are abbreviated by the initial letters of the first two words (e.g., `PL'). When requested, a separate STL file is generated containing a legend detailing the abbreviations of the button labels, with the first column being acronyms, and the second column being the full words for a button label.

Our automated design tool then places buttons on top of a thin (2 layers in Gcode, 0.8mm) flat sheet, which creates a flat surface below the buttons that is easily attached to appliances with adhesives. Then, the program splits the tactile overlay into separate groups according to the 3D printer's print bed size limit, and combines all sheets, buttons and embossed labels in each group into one piece for printing. The script can also merge multiple pieces as one print job based on print bed size to reduce print time. Our system exports files in ready-to-print STL format, which can be printed at the blind user's home or through a commercial 3D printing service. The overlay design was finalized after several design iterations as we detail in the other logs.