Pete,

Medical OC's have been, and continue to be used for glass working (beads, etc). Most seem to be rated for 3 to 5 LPM @ 7 to 9 PSI. (I typically braze at 2-3 LPM @ 5-6 PSI). Oxygen purity varies from machine-to-machine. Just about anything above 85% purity seems to function fine, the higher of course, the better. My first was an older, $150 Invacare, but I happened across a low hour, DeVilbiss 505DS w/OSD with a cracked HEPA filter a few years back for $20 at my local secondhand - cost me $25 for a replacement filer. Most OC's have hour meters so look for low numbers (below 10k is preferred). My old Invacare has 37,000 and still works fine. Be patient and selective and spend time on Craigslist.