Straight stick for the rotor
Cutting rotor 50 cm long with sharp stone
Shaving off bark
Carving a notch for the string
Fire sharpening rotor end
Finished rotor
Fallen branch from the bark fiber tree
Stripping the bark from the branch
Soaking bark fiber over night to make it more workable
Stripping the inner bark to form thin ribbons
Getting lawyer cane
Cutting the lawyer cane into 25 cm lengths to form the spokes of the impeller
Splitting the cane to form spokes
Lashing the spokes to the rotor with bark fiber ribbons
3 more pairs of spokes were attached in this way
Spokes splayed out to form a "wheel" on the rotor
A leaf is folded to form a square fan blade. Leaves are flexible and will not break if they hit the side of the blower housing (previously I used stiff bark that would often break in this way)
The leaf blade is inserted into the split spoke thusly
A total of 8 blades are now on this impeller
Making cordage from the bark fiber ribbons. Twist the individual strands one way and then back together the opposite way so that they won't unravel
Tying the ends of the spokes closed with cordage. This both holds the blades in the spokes and keeps the spokes an equal distance apart at the same time.
Completed impeller
Carving the bearing block from stone. The impeller spins in this during operation.
Demonstrating the simple string drive technique I developed. A string is laid in the groove in the top of the rotor and is wound up and pulled outward. The device spins one way then, due to it's momentum, winds the string back around it again before being spun in the opposite direction.
This effect works especially well now with the heavier spokes of my new impeller design
Getting clay for the new blower housing
Crushing up old fired bricks to act as "grog" (a material that stops clay from cracking during drying and firing). Then mixing it into the clay
Making the blower housing. I have found from trial and error that the optimal size for the housing is 30 cm in diameter (slightly less internal diameter) to accommodate a 25 cm diameter impeller. The spout coming from the edge of the housing is formed by a roughly equilateral triangle 12.5 cm to a side.
Forming the walls of the housing
For the spout use a log about 6.25 cm in diameter to form the clay around.
The total height of the housing walls will be 12.5 cm high from the ground (to accommodate 6.25 cm tall impeller blades, ensuring plenty of clearance).
Cutting a hole 6.25 cm wide in the center to hold the bearing block.
Taking the log out of the spout once dry
Making a lid for the housing (30 cm in diameter)
Molding the housing to the lid while wet (to ensure a better fit)
Cutting the air hole in the center of the lid (6.25 cm wide)
Making a tuyere (air pipe) to convey air from the blower to the fire's fuel bed during operation. The base is wide enough to cover the spout and narrows to about 3 cm at the hot end.
Drying the clay components near a fire
Wet clay is put into the hole in the base of the housing. Then the bearing block is seated into this clay (this is done so that the block is replaceable when the hole becomes too deep with use).
The sharp end of the impeller is placed into block and the lid place over the rotor so that the notched end is sticking out of the air hole in the lid
The string is placed in the notch and wound around the rotor
Then the blower is operated thusly, sucking air in through the hole in the lid and out through the spout regardless of which way the impeller spins. The force airflow makes the fire burn hotter than by natural draft alone.
Combining the blower with the tuyere delivers the air straight into the fuel bed, concentrating the combustion at a small point.
I recommend firing the clay housing when possible. Any leaks in the huts roof during a heavy rainstorm could dissolve an unfired blower housing undoing all the precision work that went into making it.
If you're only firing small pieces of pottery at a time, fill the rest of the empty kiln with unfired bricks. They often come in useful later and are easy to make.
They also protect the finer pottery above from sharp changes in temperature due to a greater thermal inertia.
This firing took about 2 hours. I knew it was done when I could see the blower housing glowing at least red hot, meaning it will not dissolve in water afterwards as unfired clay does.
The bricks are stored for the hut I built in the previous video.
Again, unfired clay is used to seat the stone bearing block in the bottom of the housing (so it can be replaced in future when it wears out).
3 impellers were made (4,6 and 8 bladed ones from left to right)
4 blade impeller
The impeller needs to be spun at a high rate to maintain a decent airflow
6 blade impeller
The impeller doesn't need to be spun as fast to maintain good airflow due to the greater blade area.
8 blade impeller
The 8 blade impeller maintains the same airflow at a far more leisurely pace. There is more torque to overcome but it feels more ergonomic as the arms don't have to move as quickly. I think 6 to 8 blades is optimal. Adding more blades after this yields diminishing returns.
Back at the new brick and tile hut...
Preparations for metallurgy are being made