This report on dehulling buckwheat was prepared by Tom Kast, who was kind enough to share the information with us and asked us to disseminate it for the benefit of our other customers:
Step 1 - Get round-hole test screens from a seed testing house such as Seedburo.com. The screens are measured in 64ths of an inch. Purchase the 9, 10 and 11 64th's screens. They are 15" square perforated pieces of metal. If you pay a bit extra they come with frames, or if you want to save a few dollars you can build the frames yourself.
Step 2 - Size your buckwheat. In my experience most kernels were larger than the largest 11 64th holes, but the value in putting the kernels through this largest screen is that all the tiny kernels fell through and could be discarded (because there were not enough to work with); otherwise, they would mix into the final result and be surprises that are very hard on your teeth.
Step 3 - Take the County Living Grain Mill and set it to a very wide aperture. Take a test handful of the same-sized buckwheat kernels and run them through the mill. Check your results. The results should be (A) All the kernels have been opened or (B) There has been little or no grinding of the black hulls which would result in "hull flour", (C) - The buckwheat is as large as you would like it (for example, Russian kasha calls for whole, dehulled kernels where as buckwheat flour can be as fine as you like).
Gradually decrease the aperture of the Country Living Grain Mill until all the kernels have been opened and before the black hulls begin grinding. If the hulls start grinding then widen the aperture a bit. Once you have the result you like, keep the setting on the mil and put all your buckwheat through the mill.
Step 4 - Take the loose hulls and buckwheat and sift them through the medium-sized test screen (10 64th's). Shake the hulls and buckwheat over a cookie sheet. This will extract 90% of the hulls which you can save to make a Japanese soba pillow. Then take the cookie sheet outside and blow lightly over the pan, shaking it slightly. This will blow off most of the remaining hulls.
That's it, you're done. Use the buckwheat flour in your favorite recipe.