I am glad you are enjoying it.I have included some math in response to ChristianSi's comment for determining the travel (pitch) per revolution based on bearing angle and shaft diameter.
In my original design I pretty much kept modifying the bearing spacing until I got the result I wanted. in my later design I put a split in the holder so the spacing is not as critical. I have been adding the shaft diameter and the bearing diameter then dividing by two and subtract about a mm to provide some tension. That is the spacing of the bearing center line from the holder center. that get's me in the ballpark.
Hope that helps.