@jason.fisher: It is worth a look. However, I won't trust it until I build a test axis. I found a professional version and they claim that the forward pitch vs the backwards pitch are within 2% of each other. Maybe we can do better. I don't know. (They seem to be concerned with compact drives instead of accurate ones.)
From their literature...
This is why I hesitate.
From their literature...
Quote
The maximum difference in pitch for the two directions of travel is 2 %. We therefore recommend the use of positional sensors for positioning applications.
This is why I hesitate.