Adapting 10 speed gearing to retro friction shifters
There are these little "caliper to cantilever" brake adapter things that increase the cable pull by roughly 33% length, and they can also be used to addapt 6 speed friction thumb shifters to pull a derailleur accurately over a Shimano 10 speed MTB cassette. They say, "You can't friction shift reliably above 9 speed." Yeah, right. It's just about pull length and cog pitch, so there are always ways. These little adapters can be had for AU$17 on eBay and will change 1.2mm pull per cog thumb shifter to modern Shimano 1.6mm mountain cog pitch.
The way they work is, the cable enters the pulley on a small diameter section, where a small movement results in a particular angular change. The cable then wraps around that small pulley and transfers to a larger pulley, fixed to the smaller one, such that the angular change results in a longer travel around the larger pulley so, as the cable exits the larger pulley, it creates a larger travel on a brake lever... or on a derailleur.
The image (courtesy of eBay seller, LilyBeiBei) shows the working, in this case, on a cantilever brake being pulled by a road leaver. (Useful for drop bar conversions of flatbar road bikes.) The eBay search term I used to find this device is, "cantilever brake adapter." Keep on hacking ugly.
July update: This will be very useful for my Triceratops One recumbent trike project, as I plan to run a 1x10 narrow/widerange gear setup on it using 6x friction thumby.