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Fanning Mill
Brief description
A fanning mill (or winnowing machine) is a post-harvest agricultural machine that uses a hand-cranked or belt-driven fan combined with oscillating wire sieves to separate threshed grain from chaff, weed seeds, straw fragments, and dust.
Use / Function
- Grain Cleaning: Cleans harvested wheat, barley, rye, oats, and rice after threshing.
- Seed Sorting: Sorts seeds by size and weight, selecting heavy, plump seeds for next season’s sowing and eliminating weed seeds.
- Scale: Farmstead to agricultural cooperative level.
Operating principle
- Feeding: Threshed grain and chaff are poured into an upper hopper with an adjustable metering slide.
- Air Separation (Winnowing): As grain falls past a hand-cranked paddle fan, a steady airflow blows lighter chaff, dust, and dry straw husks out the back of the machine.
- Screening (Sieving): The heavier grain falls onto a series of inclined, reciprocating wire sieves (riddles) agitated by an eccentric cam mechanism on the fan shaft.
- Grading: Large debris (twigs, unbroken heads) rolls over the top sieve; good grain passes through fine screens into a clean spout, while small weed seeds drop through the bottom screen.
How to create it
- Construct the Frame and Hopper: Build a sturdy wooden frame from hard Wood with an upper funnel-shaped hopper equipped with an adjustable slide valve to regulate grain flow.
- Build the Rotary Fan: Mount a hand-cranked wooden paddle fan inside a cylindrical fan housing, connected via a drive belt or gear to double its rotational speed.
- Assemble the Oscillating Shoe: Suspend a movable wooden box (shoe) below the fan exit using flexible wooden springs or leather straps.
- Install Sieves and Cam Linkage: Fit interchangeable woven Wire or perforated sheet metal sieves in the shoe, and connect the shoe to an eccentric cam on the fan axle so cranking the fan agitates the sieves back and forth.
- Add Separation Chutes: Position inclined wooden chutes beneath the sieves to direct clean grain, tailing chaff, and weed seeds into separate collection buckets.
Materials needed
- Frame & Housing: Hard Wood (oak, pine) and fasteners.
- Fan & Shaft: Iron or Steel axle with wooden paddles.
- Sieves: Woven Wire mesh or perforated Sheet Metal.
- Drive Mechanism: Cast iron gears or wooden pulleys with leather belts.
Variants and improvements
- Manual Hand-Cranked Mill: Operated by one person turning the crank while another feeds the hopper.
- Power-Driven Mill: Driven by a water wheel, treadwheel, or small engine.
- Combined Thresher-Cleaner: Integrated directly into mechanical Threshing Machine and modern combine harvesters.
Limits and risks
- Fan Speed Sensitivity: Cranking too fast blows light grain away with the chaff; cranking too slowly leaves chaff in the grain.
- Screen Clogging: Wet grain or sticky weed seeds quickly clog the fine wire mesh screens.
- Dust Hazard: Generates dense airborne agricultural dust, requiring ventilation and dust masks to prevent respiratory irritation.