How the Ledyard Sawmill Works
Lee’s Brook and the mill pond provide water for the mill
The mill pond and the 800 acre watershed for Lee’s Brook above the pond provide water to power the mill.
When the head gate in the dam is opened, water from pond flows through a channel in the dam into a holding tank on the lower mill level.
The water turbine and power train
The holding tank is connected to the Tyler water wheel turbine which can be seen in the turbine pit in the mill lower level.
A gate on the input port of the turbine is geared to a handwheel next to the saw on the mill main level. Turning the handwheel opens and closes the turbine gate, controlling water flow from the holding tank into the turbine.
The vertical turbine shaft is geared to a horizontal shaft that ends with a heavy iron flywheel and crank under the saw.
A wooden pitman arm connects to the crank to the wooden saw sash, converting the rotary motion of the flywheel into an up and down (reciprocating) motion.
A pulley on the horizontal flywheel shaft also provides power when the log carriage is reversed when each sawcut is completed.
Water exits through the bottom of the turbine and flows out through the tail race, a channel cut through the lower level of the building, before joining the brook downstream from the pond.
The saw cuts on the downstroke and the log moves toward the saw on the upstroke
When the turbine is opened with the handwheel, the saw sash reciprocates about 100 strokes/minute. The six-foot millsaw fixed in the sash cuts on the downstroke, and on the upstroke the log carriage moves toward the saw.
The millsaws are sharpened by hand with a file. During typical use, we can saw a couple of logs before the teeth need to be touched up.
The movement of the log carriage is adjustable from 1/8" - 3/4 per stroke. The saw is adjusted carefully in the frame for the amount of cut. Originally, the the saw would have been used to cut as fast and efficiently as possible which is dependent on pond level, the size of log and hardness of the wood, and the condition of the saw teeth. For demonstration, we saw at the smallest log carriage feed rate of 1/8" per stroke which yields a sawing rate of about one foot per minute.
To advance the log into the saw, the movement of the carriage is synchronized with the stroke of the saw. As the saw rises, a connecting arm on the top of the saw sash is linked to a rocker and then to another arm that pushes forward on the ragwheel, a four-foot diameter wheel rimmed with ratchet teeth. The ragwheel shaft has large wooden teeth that engage corresponding holes in the bottom of the log carriage and move it forward on the upstroke of the saw.
The end of a cut
As the cut nears the end of the log, the carriage is stopped by lifting the pawl off the ragwheel.
We don's saw through the end of the log, rather the sawcut is stopped just short of the tail block, leaving 3-4 inches of the log unsawed. (The broad bottom of the log and the weight from leaving unsawed boards on the carriage help stabilize the log during sawing.)
The log carriage is reversed by pulling a lever that engages a small bevel gear to the teeth on the side of the ragwheel. Power to reverse the log carriage comes via the a pulley and belt on the flywheel shaft in the lower level. The log carriage backs up to the starting position and then turbine gate is closed to turn off power to the shafts.
The log is moved into the position for the next sawcut, or if sawing is complete, we split off the sawn boards for stacking.