Using the manual Baesa Corn mill installed with a 1/2 HP motor and burrs with narrow teeth. The teeth were flattened and made more even on a lathe machine.
The cocoa nibs should be ground while still warm or the cocoa butter is still in melted state. Roasted cacao today, winnowed tomorrow and ground immediately after is still good. If let past for another day, the motor will have a very hard time reducing the nibs to smaller sizes and waking the oil up. It is going to clogged most of the time. Dropping the nibs little by helps but makes the grinding very very slow. Reheating the nibs using mild heat is recommended. Take good care not to overroast. The first grind pass should be fluid enough to be driven by the auger for the second and subsequent pass. If not, it needs a push, like what meat grinder and ice crusher are doing. I am hoping it is as easy as writing few sentences.
Using the portable mill, 1.5 HP with grinding stones.
I was wary at first. Rotating stones when touched each other might broke. I was glad my thought was wrong. The grinding stones are easily scraped by an iron file but never when rubbing against each other. The high rotational speed of about 1700+ rpm is not enough to cause breakage. If run for a long time without a load or on a too tight setting will result to a burnt odor typical of a cigarette butt.
It can grind newly roasted and winnowed cacao fast. Almost triple the time required using the ordinary mill above. Second pass seems okay. The trouble comes in the third pass. Cocoa liquor seems like Elmers Glue holding the two stone faces together and stopping the motor rotation. The liquor flow should be regulated to the point that it never put too much burden to motor.
Grinding stones, unlike metal burrs never heat too much. It is beneficial for preservation of delicate flavors but not to grinder operation. Cocoa liquor is indeed liquid when hot but becomes viscous as temperature gets colder up to the point it hardens.
The machine is easy to disassemble and clean but the food debris on the stones are really hard to removed. The cocoa color just stays there no matter how many times I wash it.
I have not fabricated yet my very own grinding machine design. I think I have to make modifications in advance.