Our walnuts, Chandler, are oval. If they were circular it would be easier to size them. Last year we tried sizing them optically, but the camera and computer had difficulty knowing whether it was measuring the length or the breadth. Sometimes two walnuts landed on the same key and were measured as one huge nut.
So this year we have found another method. A small company in a small town in North Dakota makes a machine which they claim sizes walnuts. Their web-site says they have been manufacturing since 1935, presently have over 15 staff and a turnover in the millions. The dried walnuts are fed in to a hopper. From there they pass onto a conveyor with bars that gradually separate from each other as the nuts travel. The sized nut falls onto another moving belt running perpendicular to the top conveyor and into a fruit bin.
In readiness for next processing season our small farm is importing a sizing machine capable of assessing eight tonnes of nuts per day from a small company based in a tiny township in North Dakota. Wish us luck.