A binary ink developer assembly includes a plurality of rollers, gears, and end caps. The rollers are in contact with each other to form a nip. Each roller includes a plurality of bearings. The gears include gear teeth. A respective gear has an involute tooth profile and applies a gear force at a pressure angle corresponding to the involute tooth profile to rotate at least one roller. The end caps are coupled to the bearings. At least one slot arranged to form a slot angle substantially equal to the pressure angle and to receive a respective bearing to support a respective roller.