" And so, the question: Has anyone here had success with this scheme before? If so, any hints or suggestions? Am I aiming for the 5mm pitch spacing required for a campag set-up, or something between this and the 4.8mm shimano requirement?"
I've thinned spacers to make a fracansette
Mine was all Shimano, but I'm using EIGHT 7 speed cogs on an 8/9 speed free hub body to make my home brew 8 speed.
I did all the math, but it didn't work out. Fortunately, I needed to thin the spacers a bit more, so no problem, It's difficult to make them thicker again
1st- DO NOT use power tools! They are faster than you are.
I had a 100 grit emery belt for a belt sander. After destroying the first spacer, I took the belt off and laid it flat on the bench.
The Shimano spacers have the 3 holes that the rivets pass through, so you can use them for reference.
I started off with 20 strokes, rotate 1/3 turn, 20 more, rotate 1/3 turn and 20 more. MEASURE in 3 places to make sure it's not getting lopsided.
I did all the spacers, and when I thought I was getting close, I assembled the cassette onto the FH. Since I have friction shifters, my main concern was getting them even and enough to seat the lock ring properly.
After going through the first step with all spacers, you have a real good idea how much pressure to use and how much you remove per X number of strokes.
I had to repeat 2 more times, but I wanted to "ease in" to the right stack height.
When you measure, compare ALL the spacers. You'll probably find a couple thou variation, so you can adjust that in steps 2, 3...etc.
The spacers I had, had "ridges" on the flats, so the ridges sanded down quite rapidly, compared to the rest of the spacer. Probably .004" per side?
Just take your time and check often for parallelism and spacer to spacer consistency.
Not ALL 7 speed cogs are exactly
the same thickness. You might check your cog thickness. Both my "parts cassettes" were Shimano, but different quality levels.
I'm still probably about 1/2 turn from seating the lock ring "properly, but it seems to work fine enough, so I called it good.
BTW, standard SHimano 7 speed spacing is 5MM.
Also, maybe the alternate cable routing method may be of some use?