I made a right mess of the first design, not only did I get the angle wrong but the second opto is also at the wrong radial distance, which is why its amplitude was less. So I had to redesign the bracket, here is my second attempt: -
The correct angle for quadrature needs to be (K + 0.5)(180 / n) where n is the number of slots in the wheel and K is an arbitrary integer. The first convenient angle which straddles the bolt through the motor is 45°.
A single coat of BBQ paint seems adequate to block the IR beam.
A bit of a pain to wire up! If it proves to be a useful encoder I will design a pair of PCBs.
The waveforms are now both full amplitude and in quadrature: -
The edges are slow because I am using 4 pin optos, Zach seems to have bought up the world's supply of the five pin ones for the RRRF! The five pin versions have a built in Schmitt trigger to square up the waveform before it goes down the cable. Most micros have Schmitt trigger inputs these days but the disadvantage is that any noise in the cable will advance or delay the edge slightly, giving a timing error. Given the imprecise nature of this encoder I don't think it will make much difference.