Power Transmission Ben Thresher's Mill, Barnet Vermont
In 1836 a dam was first built here and a saw mill operated on this site from 1836 until c. 1855. The type of construction of the first wooden dam is unknown. It was possibly similar to the present timber frame and plank dam. In 1872 a wooden dam was built and a vertical turbine with a square penstock was installed. The first turbine was replaced In 1911 with the present Rodney Hunt horizontal turbine. The present dam has been repaired many times. It was not entirely destroyed even in the 1927 flood which caused extensive damage all along the Stevens River.
The present timber frame and plank dam is 135' long including 40' of stone under the north end. This additional support prevents the swampy end of the mill pond from washing out. It is not known when the stones were put here. The wooden dam is constructed of heavy timbers; trees or beams and planking; hemlock or tamarack lumber. Upright timber supports are pinned into holes drilled into the rock ledge of the Stevens riverbed. The height of the dam varies from 5' at the north end to 10' at the south end near the gate. Small cracks between the planking are filled with clay or clinkers from the forge. Later, after the gate has been lowered, river silt will fill in the cracks and allow only minor leaks. The wooden gate is raised and lowered by hand. When the gate is lowered, the river begins to back up and creates a mill pond behind the dam. Water is free to flow through a wooden trash rack at the northwest corner of the mill. At this point, water falls into a wooden pit and enters the penstock. In the Summer of 1979 the dam was repaired and there is about 14' of head water.
The first ten feet of the round penstock is a sixty-inch diameter steel boiler with the ends removed. The last thirty feet is a wood-stave penstock that delivers water into the turbine. The penstock is thirty-six inches in diameter and is strapped together with iron rods.
The 1911 horizontal turbine has a cast-iron case, and the eighteen-inch runner turns in water-lubricated wooden bearings. The turbine is a "left-hand" type, meaning that the runner turns counter-clockwise as the water enters. Water flows out a thirty-inch diameter draft tube which is nearly eight feet long and empties out the bottom of the tube onto the rock ledge and into the river. The main drive shaft runs out the back of the horizontal turbine and rests on concrete bearing supports.
All the line shafting in the mill is powered from the main drive shaft. The turbine can be opened from a wheel control on the first floor (near the surface planer) or from a small hand control in the cellar. The main drive shaft (3" diameter) from the turbine turns a forty-inch wooden flywheel. The large flywheel is engaged with a belt tensioner manually activated from upstairs near the surface planer.
Three line shafts drive the machinery upstairs in the mill. The first (north) line shaft powers the pattern lathe!, belt sander, power threader and engine lathe, all located along the north wall on the first floor. The second line shaft powers only the wood planer located in the middle of the shop. The third line shaft powers the jointer, both table saws, band saw, wood lathe, grindstone, drill press, boring machine, trip hammer and the cordwood saw (located outside the mill on the south wall). All machines are belt driven from pulleys on the three shaft lines in the cellar. The third line shaft is extended into the Cider Mill and powers the apple grinder and the hydraulic mechanism. There is no power machinery on the second floor or in the attic.
The 1923 six-cylinder Studebaker engine has a fly-ball governor to regulate the speed. The engine is still in place in the cellar of the Blacksmith Shop. It was used to power the mill in times of low water or repairs but is no longer in use. The John Deere crawler tractor can be employed to power the mill. It sits in the driveway and from its power-take- off a long belt runs to a pulley on the main shaft in the cellar of the Blacksmith Shop.