Anfim Super Caimanos have been rocking an amazing set of 75mm burrs for around 10 years now (I can't remember when this was posted: http://espressovivace.com/equipment-rev ... o-grinder/ it could be longer but I can't dig up any documentation to support that). I'm a huge Anfim SCB fanboy despite having moved on to other grInders.

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!

A/C motors usually require a variable frequency drive for lower RPM. This also requires lowering the applied voltage in step with the frequency reduction or you will let the magic smoke out of the motor. Just reducing the voltage to lower speed is also usualy a fail as the torque drops dramatically and the internal heating goes way up.

Rich, good point... but I'm too lazy to look for a VFD and don't know much about them. Besides, I have the variacs already
The motor in the SJ looks really substantial and has big, heavy armature... I was hoping the torque would be sufficient even when slowing down simply due to the sheer amount of rotating mass inside the thing. Will find out the hard way, I suppose... only one way to find out.

Bigpaul, I'm not sure about a 12v solar application. Solar seems to be standardizing around a few select voltages, 24v and 48v seem to be very popular. I have a small 24v system myself... 4 golf cart batteries wired in series. It powers my chest freezer with 3 solar panels but in real use, it seems that most days, I end up switching that freezer back to mains power before going to sleep... around 11pm. Then, I switch it back to 'solar' in the morning before leaving for work. The thought is to use the free sun power during the day... but batteries are expensive, so I only have a minimum set to buffer the power sytem flow, and not really set up to use them at night for very long, since that would require a much larger set of batteries than I'm willing to pay for (they require changing the entire set every few years). I stayed away from 12v because it shows too much voltage sag, especially when you turn on big power hogs like blenders (or coffee grinders... or heaters of any kind, like my Strega, dammit!). Stand alone solar NEVER pays for itself, its much much much much much too expensive when you consider the cost of the batteries. My system that I put together was for me to gather more data to see how much the real world costs would be over a few year period. Supplemented solar (connected to the power grid) is a different story, though... if the daytime 'banking' costs are reasonable with your power company.

a Vairac will likely not work that smooth as Rich mentioned, VFD is cheap nowadays; 70$ https://www.ebay.com/itm/220V-0-75kW-Si ... SwhcNaXW7Y
(no clue if this example will work, I plan to tinker with some used VFDs on my mazzer -a friend of me has some lying around for a turn table project)