A openscad parametric rotary encoder.

It features two options to drive this encoder.
First option is over the shaft. Second options is to use the encoder as a wheel. If you change the wheelGrooveDepth parameter, a rubber O-Ring can be put on to the encoder.
Openscad file "encoderWheelMK1Oring.scad" is a example configuration for use with a O-Ring.

Changeable parameters, with default values:
shaftDiameter = 3.30;
wheelDiameter = 28;
shaftMargin = 2.5;
shaftHeight = 5;
shaftBevel = 0.3;
wheelHeigh = 0.75;
wheelGrooveDepth = 0.0;

encoderInnerRadius = 9.5;
encoderOuterRadius = 13;
encoderSlitWidth = 0.8;
encoderSlitMargin = 0.8;
encoderSlitCount = 35;