Educational Tool for teaching Fractions to the Blind. Source: Archive.org Alexander Mell, Der Blindenunterricht. Vorträge über Wesen, Methode und Ziel des Unterrichtes in der Blindenschule, 1910 This is just a first quick draft. You probably need to adjust minimum thickness and gaps for this to work on your 3D printer. I didn't have the opportunity to 3d print this, yet. In case you do, please let me know how it worked out!