We visited Mostert’s Mill on a misty Saturday to watch them mill wheat. This mill was built in 1796. It is just a small mill built for one farm that sat on the slope of the Liesbeek River Valley in what is now Capetown.
Wooden gears
This was one of the first independent mills as before this the Dutch East India Company held a monopoly to provide grain for the garrison and the ships berthing in Capetown.
The interior of the mill is primarily wood that had been salvaged from ship wrecks on the beaches of Capetown and False Bay.
The main gear cogs are of beech. The drive shaft cogs are acacia.The drive shaft is a ship’s mast. The mechanism is simple and elegant.
The gears are lubricated with melted beeswax to ease their meshing as they drive the mechanism. The main drive shaft and rotating roof framework is lubricated with lard.
The walls of the mill are built of rough stone with a limestone mortar. The walls are covered with a limestone skim coat with limestone white wash. This wall covering allows the walls to breathe and has allowed the existence of the mill to this day.
The roof is thatch supported by wooden dowels laid over with woven reeds. This must be replaced at regular intervals due to the nature of the materials. Roof thatchers still have a lively business in Cape Town.
Mounting the Sails
The mill is driven by wind power. Canvas sails are mounted on four wooden trellis structures set at 90 degree angles to each other. Sails and runner boards can be added or removed to adjust for wind speed.
Directional Control for Sails
The sails are mounted on a circular brace that circumscribes the lip of the roof and allows the sails to be adjusted to face into the wind.
The roof position and directional control for the sails is provided by a beautiful gear mounted at human height on the outside of the mill wall
The miller on the day we were there was Peter, a volunteer who has been trained by millers from Holland. He and another group of volunteers care for the mill.
The miller
This means running the grinding and sail mechanisms periodically to be sure all is as it should be.
The mill is run today with the same mechanical systems that produced wheat flour for a farmer, his wife and 40 slaves in 1796.
That original technology is tried and true.
MedFlies 
To fabricate that huge circular wooden gear, they must have spliced formed segments……curious as to what kind of splice joint they could have used……..dovetail maybe, could you tell?
Near as I can tell from the photos there are four wooden half moons. These are solid, one-piece slabs.These are slotted into each other and secured with wooden pegs. Then four iron strips are bolted to the wooden structure in a square to reinforce it. What you have is the circular gear with a square iron infrastructure. Very simple and long lasting industrial design.