About a month and a half ago I picked up an used BUNN LPG from a local Italian restaurant. The owner originally wanted $350 for it, but after some time, I showed up with $160 and waved it in front of him and he accepted.
I took it home and immediately took it apart for a good cleaning. I even found a dead cockroach inside! The hopper was yellowed and cracked, the solenoid operated 'gates' were scary and the entire unit was far too big for what I was using it for, which is a cupping/Chemex grinder. I promptly removed the hopper and used a piece of PVC pipe to go over the motor assembly to prevent stray beans from popcorning out during grinding.
Then I had the 'great' idea to get rid of the solenoids and gates, get rid of the huge switches on the front and operate the entire unit using a pushbutton. The idea was that I could hold down the button to turn the grinder on, and let go to turn it off. Simple enough. Trouble was, like a tool I didn't look at the wiring diagram and I miswired the darn thing. I blew a fuse, and after a lot of time I finally connected the motor to the AC line. It 'moved' and I assembled everything back up. When I put beans it, I found that there was no grinding, the motor was moving but it was more of a vibration than a revolution. My worst nightmare had come true, the control board and fuse that I blew out during my failed experiment was actually converting the AC current to DC current, and this motor was DC!
All sorts of crazy ideas came through my head at this point. Should I get a three phase AC motor from craigslist, modify it and use it as a new motor? I already have access to 'free' AC drives from my company. After a lot of thought, I decided it would be best to scrap the entire control board, streamline the profile of the grinder and attach a Variable Frequency Drive to the motor. I wanted everything to be clean and minimalistic, and I made the top portion of the machine 'modular' when it comes to wiring. This means I can disconnect 4 wires and remove the entire top of the unit to service the burrs when need be.
Have a look, I hope you enjoy.
One more thing, the 'plug' which you see on the side is actually an 'explosion proof' unit that I took from a dumpster at our company's R&D facility. The box it came in had Japanese writing on it and when I saw the quality of it, I was shocked that they threw it out. I had no idea what I would do with it many months back, but I knew it had a purpose. Now, it belongs on the machine and looks the business.
The issue of popcorning: I start the machine with the slowest setting for the motor which is a complete standstill. From there I add a little bit more power until the shaft starts to rotate. At this point, the shaft might still lock up due to the torque required to grind the beans. I then adjust out the power until the shaft is rotating as slowly as possible but NOT locking up. I've found that at this speed, popcorning is not an issue. I've also created a temporary cardboard cutout to put over the opening just in case.
Once I put the Ditting burrs in, I would like to do some experiments to see how the speed of the grind influences its consistency.