How to Build a Fanning Mill
A fanning mill is a filtering device for cleaning shelled corn. It removes dust, hulls and corncob from falling shelled corn so it can be cleanly burned in a pellet stove. They were originally built on a gravity-fed process that screened out the larger pieces of waste material. The semi-cleaned corn then fell through a chamber and air was forced, or fanned, though the chamber to blow out hulls and dust as the corn fell. All this was done so that the corn could be efficiently burned without producing soot and smoke.
Build the cabinet
Use a framing square and pencil to measure four pieces of 3/4-inch plywood. Two -- the side panels -- should be 12 inches wide and 40 inches long. The other two should both be 13 1/2 inches wide. The front panel should be 22 inches long while the back panel should be 40 inches long. Cut them with a circular saw and sand all the edges.
Draw two diagonal lines on both of the side boards. These lines should be from side to side with the first line starting 4 inches below the top and extending down at a 40-degree angle to the other edge. The second line should start 1 inch below the endpoint of the first line and running back in the opposite direction, also downward at 40-degrees. These are mirror-image lines inside the boxed frame; the left side lines run from upper right to lower left and the right side lines run from upper left to lower right. These will support the 1/4-inch screens.
Draw another line -- squared and horizontal -- on each of the side boards 3 inches down from the top. Drill three 1/8-inch holes on all the lines, equidistant apart, on both boards. Turn the boards over and power drill two 1/2-inch wood screws through all the holes. The parts of the screws that extend into the cabinet become the support points for the 1/2-inch screen.
Measure and mark the drill spots on the outside -- without the lines -- of the side boards, at the edge, for connecting screws. On the back panel connections there should be one hole 2 inches from each end and three holes -- at 10, 20, and 30 inches. The front panel should have only three drill spots -- at 2, 10 and 20 inches. Assemble the cabinet with right-angled corners. Hold one side vertical against the back panel lying flat. Drill a 1/8-inch hole -- 3/8-inch from the edge -- through the vertical board and into the center of the back panel lying flat. Power screw one 1/2-inch wood screw to connect the boards at the corners.
Draw a horizontal line on the sides of the cabinet 15 inches up from the bottom. Drill three 1/8-inch holes equidistant apart in each line on both sides. Drive two 1/2-inch wood screws into the holes, which become base-plate supports on the inside of the cabinet. Measure and cut a piece of plywood 12 inches by 12 inches for the base-plate.
Measure and mark a 5-inch arch at the bottom of the cabinet sides to form the side feet. Do this by laying the cabinet on its side and holding an old CD at midpoint on the bottom edge of the cabinet, drawing a pencil line around. Use a keyhole saw to make the cuts on both side panels.
Measure and cut a piece of the plywood 2 inches wide and 13 1/2 inches long. Drill and screw it to the front of the cabinet sides 2 inches below the bottom edge of the front panel. This piece forms the lip that the right-angle duct will rest on as it is inserted into the space above it.
Measure and cut a hole in one side of the cabinet with a 2-inch hole-saw (circular) bit. This hole should be 20 inches from the bottom of the cabinet and near the front panel. It is the vacuum exhaust port. Cut a 2-inch piece of 2-inch PVC pipe to fit inside the hole and connect to your shop vacuum.
Assemble the Mill
Measure and cut two pieces of 1/4-inch galvanized mesh with tin snips. Both of them should measure 12-by-17 inches. Measure and cut a 12-by-12-inch piece of 1/2-inch galvanized mesh.
Insert the two pieces of 1/4-inch mesh, and weave the edges onto the top screws to prevent the screen from sliding down. There should be a 1-inch slot at the bottom of the screen that allows the non-screened corn to fall through. Trim or re-cut as necessary. Insert the square piece of 1/2-inch mesh and ensure that it lays flat on the support screws. This screen catches anything larger than 1/2 inch.
Insert the plywood base plate at an angle and allow it to settle against the support screws. Insert the 2-inch PVC pipe into the cabinet and seal both sides with wood putty. Insert the HVAC 90-degree end boot into the 2-inch slot above the plywood strip at the base of the front panel. It should fit snugly without calking. Connect your shop vacuum to the PVC exhaust pipe. Place a 3-gallon bucket under the end boot to catch the corn.
Things You Will Need
- 3/4-inch plywood
- Framing square
- Circular saw
- Power drill
- 1/8-inch wood bit
- (1) 1/2-inch #8 wood screws
- (2) 1/2-inch #8 wood screws
- Power screwdriver
- Keyhole saw
- 2-inch hole-saw bit
- 2-inch PVC pipe
- 1/2-inch galvanized 19-gauge wire mesh
- 1/4-inch galvanized 23-gauge wire mesh
- Tin snips
- Wood putty
- HVAC 90-degree 2-by-12-by-6-inch End Boot
- The vibration of the shop vacuum will keep the corn moving.
- Consider adding an optional hinged lid.
- Wear hearing and eye protection when using power tools.