Thanks Brucey!
A few questions:
Where can I get a spacer with cut-outs in it for the new #1 sprocket from?
It looks like quite a few (not all) cassettes have loose sprockets for the #8 position, that can probably be removed easy enough, but many seem to have the #1 sprocket fixed to a carrier (like my current Shimano XT 11-32 cassette, in fact all sprockets are fixed to a carrier for that cassette), not sure how one can be sure when buying a cassette with a 32T sprocket whether that sprocket (and the #8) is easily removable?
Where would I source a different lockring from? If, for example, I'm trying to make a 13-32 cassette, does that mean I need to use a locking from a cassette that starts on 13 (e.g.a 13-25)? If so, then this implies you'd have to use 3 cassettes to make a 13-32 one, or can lockrings be purchased seperately?
Where can I get the sort of spacer mentioned in point 4?
Not sure I fully understand point 6...
This is starting to look a bit too complicated for me and my limited workshop skills... :-(
Also, looking at geat calculators and thinking about my use cases, I think a 12-32 may actually work better for me than a 13-32 - with a 46T front ring the highest gear would 112.9" for 11T, 103.5" for 12T, but only 95.5" for 13T - this compares to the 103.1" I currently get from an 11T cog with a 42T front ring, which is a gear a use every morning when cycling down a long hill to get to work (could even do with a bit higher). I don't think I would want to reduce my highest gear to less than 100". IRD do an off the shelf 12-32 cassette in their lower-end "Comp" range (SJS sell this) - the small gaps between the gears sound quite nice, but is the smoothness and speed of shifting likely to be worse than my Shimano XT 11-32 cassette? The IRD cassette is certainly heavier!
IRD Comp 12-32 (Shimano-compatible)
12, 13, 14, 16, 18, 20, 24, 28, 32T
Shimano XT 11-32
11, 12, 14, 16, 18, 21, 24, 28, 32T
So the IRD would have smaller gaps between 12 and 14 (due to the additional 13), and only 2T difference, instead of 3T, between 18T and the next cog. The gap between 24T and the next cog down is one larger, but that's less of an issue.