understanding 3 speed gearbox conversions

[JonE]

  gearbox photo 1.jpeg (Size: 78.75 KB / Downloads: 812) There is a lot of literature on 3 speed conversions but it is difficult to understand exactly what happens from the various diagrams and descriptions. Can anyone eluicidate for the non-engineer, from first principles? This diagram I think is Mike Phelan and has been the most helpful one from the web. Woodrow and the Green book don't actually manage to explain; they preach to the converted.

1. I can't work out how reverse actually works from the diagram. What is the relationship between the 12 and the 16 there? Or is the 16 just a different position of the central lower 16 cog pictured a little to the left?

2. Andes Gears. Mentioned on web from discussion from Vince Leek and Andrew Bird, 18/24 or 20/24 2nd gear pairs. Do these just plug and play into the position of the 20/22?

3. Close ratio conversions otherwise seem to involve the input shaft being machined to replace the 14 (and 28 as a result to maintain the pair)

Would be interested to hear what others' explorations have found. Thanks...