big paul, I treated myself to some wake up therapy and decided that instead of building something up from scratch (I had actually priced out a treadmill on amazon which I was on the verge of ordering, in order to cannibalize the dc motor and control electronics to use in my grinder, about $300) I could just cut to the chase and... use something else that someone else has already designed and built to do the same thing, as a starting point. I bought a used super jolly off the 'bay and have been modding that... its under the thread "Attack of the 75mm frankenjolly" but its not complete... its a/c though, but I haven't done any calibration tests yet. I want to fire the tach at it to get a baseline speed, then plug it into a variac and see if it will retain enough torque to do a good grind job if I slow it down to near 400rpm. that will be an interesting test, and costs me nothing since I already have a couple spare variacs on hand since decommissioning my air popper/roaster (bought a kaldi roaster). but there's SO MUCH to do. I was going to try to use the 75mm mythos burrs in the SJ.... and found that actually, I COULD... but but but. The burrs actually appear to have the same bolt pattern, so you actually COULD bolt on a set of 75mm mythos burrs into any SJ... on the top carrier. And the burrs DO FIT into the grinding chamber of the SJ (lower carrier). Just barely. So on the bottom carrier, it will fit... but the 75mm burr 'floats' on the tops of the sweep fingers (3 of them) that normally are there to sweep the grinds into the chute. The ground coffee exits the burrs on the periphery of the burrs, so you are supposed to have a small space there, and the SJ has small aluminum 'fingers' that sweep the coffee toward the hole which then turns into a chute to exit. But the 75mm fit is so tight, it just barely fits into the chamber and the only way to bolt the 75mm burrs to the lower carrier would be to cut the fingers off. I played with the idea of doing that, then enlarging the grinding chamber diameter slightly, then rebuild the 3 fingers a little bit farther out into the newly cleared space... but then, you wouldn't be able to take out the lower burr carrier if you cut the chamber slightly larger... the 3 fingers would now bind as you tried to lift it out for servicing/cleaning. Sooooo... what that means is, you'd have to cut the chamber slightly bigger all the way to the top, which has the fine threads for the grind adjustment. New threads would have to be cut... and the existing top burr carrier would no longer fit, so you'd have to make a sleeve for THAT and cut the same new threads. Just a huge can of worms, and I'm still chewing on it... is all that really necessary?? Almost easier to just build from scratch with the dimensions I want, so I'm back to square one.
Cwd, the alignment of the parts in motion doesn't really scare me. People do it every day, all the time.... just that most of the time, such alignment exists in machines not purpose built to grind little beans. They're called lathes and mills, and usually they grind pieces of metal... but alignment is critical in that environment and its not unusual to see tolerances approaching tens of millionths of an inch. Easily more accuracy than I'd need for a coffee grinder, just that I don't want to build my coffee grinder around my mill or my lathe. Then every time I needed a cup of coffee in a different place, I'd have to hire a forklift to move the machinery
AND wipe all the coolant and oil off the coffee grounds. What a mess!