A hand-powered backup mill keeps a village fed when the wheel, sails or animals are down, but it costs far more labor than a powered mill: a worker turning a quern grinds about 2.7-5.4 kg of grain an hour, so a village of 100 that needs 68 kg a day spends 13-25 person-hours grinding. Keep a backup able to grind a few days of coarse flour, not the whole season.
Part of Community Grain Mill
Hand-driven grinding as insurance for a powered mill: the quern, a crank on the main stone, and a walked capstan, with the labor each takes.
Hand Grinding Is The Floor, And Its Labor Sets The Case For A Mill
The carrier gives a hand quern with a 12-18 in stone at 0.1-0.2 bushels an hour (and 4-8 lb of flour an hour, which is about two-thirds of the grain by weight, so the two columns agree). At 27.2 kg a bushel of wheat that is 0.1 x 27.2 = 2.7 kg to 0.2 x 27.2 = 5.4 kg of grain an hour. A village of 100 people eating 1.5 lb of grain each a day needs 150 lb, which is 68 kg a day, so hand grinding takes 68 / 5.4 = 12.6 up to 68 / 2.7 = 25 person-hours a day, 13-25 in round numbers. The same grain on a mill that can turn for 1-2 hours takes a handful of people for part of a morning.
The effort per kilogram is the other side of the same figure. A person can hold about 50-100 W at a crank for a working spell (a recalled range, not a measurement), so 50 W / 5.4 kg/h = 9.3 Wh/kg up to 100 W / 2.7 kg/h = 37 Wh/kg. That overlaps the 15-60 Wh/kg grinding-energy band used throughout this batch, with its lower part falling below the band’s start (Bushels per Hour by Power Source).
Three Backup Forms
The rotary quern. A small pair of stones with a wooden handle (Rotary Quern) can be made by anyone with stoneworking basics and kept as the smallest backup. One person sits and turns it.
A crank on the main mill. A detachable cranked gear or lever arm fitted to the stone shaft lets people turn the full-size stones when the wheel is dead. The stone nut on a water mill can be disengaged from the drive (Clutches and Engagement); the same arrangement lets a crank take over. The crank turns the shaft directly, so it needs none of the rotation-to-reciprocation conversion that a pump or trip-hammer crank does.
A walked capstan. Several people walk a bar on the upright shaft, as a horse does. Four people at 50-100 W each give 200-400 W at the bar, and after a two-stage train at 0.81 that is 162-324 W at the stone, which is 162 / 60 = 2.7 kg/h up to 324 / 15 = 21.6 kg/h. This is the practical way to get a horse-gin’s order of output when the animals are not available.
What You Need
- A rotary quern of 12-18 in stones, dressed and ready (Stone Dressing)
- A way to couple a crank to the main mill, or a capstan bar on the upright shaft
- A rota of people, since a crank is tiring and each should work short spells
Method: Keeping The Backup Alive
Step 1: Test it every season. Run the backup at the start of each milling season so a seized crank or a dry bearing is found when nothing depends on it.
Step 2: Store coarse, not fine. A backup is for coarse meal and porridge. Fine flour takes the most energy per kilogram, so leave fine sifting for the powered mill.
Step 3: Grind to a plan. Do not grind more than the next few days’ need; whole-grain flour goes rancid within weeks.
Worked Example
A village of 100 loses its wheel for a week and needs 68 kg of flour a day. One capstan of four people puts 162-324 W on the stone and grinds 2.7-21.6 kg/h. At the high end the day’s 68 kg takes 68 / 21.6 = 3.1 hours of running; at the low end it takes 68 / 2.7 = 25 hours, which is more than a day, so a second grinder such as a quern or two must run alongside. The wide range is the point: until the capstan has been timed on real grain, plan the backup for days, not seasons.
Common Mistakes
- Treating the quern as a plan. 13-25 person-hours a day is a large share of a village’s labor for bread alone.
- Never testing the crank. An untried coupling fails when needed.
- Hand-grinding fine flour. It takes the most energy per kilogram; grind coarse and sift later.
Cranks, kickback and dust
A crank handle on a geared stone can spin back if the stone slips or the drive engages unexpectedly, and the stones can crush fingers at the eye. The stop is a person at the crank who lets go and a disengaged stone nut; disengage the powered drive before fitting the crank and keep hands out of the eye. Flour dust is explosive in a cloud, so sweep often and keep flames out of the mill.
What’s Next
- Learn next: Millstone Construction - the stones that all four power sources turn
- Combine with: Mill Power Sources - choosing among the sources