You can easily get caught up in the bike industry's definitions of things and start arguing in their terms, forgetting to analyze problems at their most basic level. Nowhere does this seem to exert more control than in drive trains.
I spend a lot of time getting people's shifting to work. I spend time getting other things to work, too, but shifting occupies a lot of brain space, working out compatibility issues and remembering what can and can't be fixed at all.
Aside from the fixed-gears, my other bikes have seven or eight speeds. My faithful old road bike had seven because I had never re-spaced the frame to 130 mm and I had a wheel with a seven-speed hub without too many miles on it. But commuting to work I discovered two things: First, I wanted a slightly lower low gear. The old 26-tooth cog, even with a 34 ring up front, was good enough for the relatively easy commuting route, but gave me no reserve for longer, nastier climbs. Second, I liked the 50-26 (The Ned), but I feel guilty using it.
I wondered if I could build an eight-speed cassette from nine-speed cogs and spacers that would then fit on a seven-speed freehub.
Yes I can.
Miche cogs and spacers came today I test-stacked them on a seven-speed hub from the box of salvage in the basement. Perfect! But would it work with my eight-speed chain? Not a big deal. Nine speed chains are a little more expensive, but still cheaper and more durable than 10- and 11-speed chains. I'd done some experiments on particularly troublesome drive trains that indicated you could run eight on nine and nine on ten in a pinch. And that was on indexed brifter systems. Shifting in friction opens up a lot of other options. If I didn't mind joining the Chain-of-the-Month Club I could make 11 on eight. Ten, anyway, but that's not exotic.
The road test disclosed no problems. I can shift the whole range from both chain rings. I've got my former Ned as a legitimate choice. The new Ned works, too. The chain was long enough.
Of course the disclaimers say you should never mix brands and types of cogs, bla bla bla. If you needed precise indexing performance that would be true...ish. I've mixed cogs for special needs indexing customers as well as friction shifting privateers. It's dicier when indexing is at stake, and downright impossible for the obsessive shifting-geek who thinks a Wippermann chain is "too noisy and slow." Someone that addicted will sell an organ and a couple of kids to have a directional Dura Ace chain when he needs it. Face REALITY, dude! You need help!
Shifting a crowded cluster in friction takes a light touch. Actually, this latest Frankencassette is not as touchy as I though it might be. The Campy Veloce derailleur was already very quick compared to the agglomeration on my Cross Check. Closing up the spacing and adding a cog has not made it unmanageable.