I used to make fixed wheels out of old (schwinn or whatever I could find at the dump) road wheels. I would dismantle and pull the whole freewheel assembly off the hub, remove all the cogs except one of the threaded ones that are used to hold the whole thing together, then I would put it back together and weld the internals, then the cog to the freewheel assembly, then rotofix it to the hub. Worked ok up until I started running ~85 gear inches, then I started bending axles on tough climbs. (couldn't re-dish the wheel because the assembly was the same size as a 5 speed). Finally have a proper track hub and can't belive the difference.

Also made a bunch of choppers and tallbikes from scrap.