  |
 |
|
|
The hurst frame supports the gearing and the millstones. It is a timber frame structure which is self standing and is isolated from the walls of the mill building so that the walls are not damaged by the vibration of the machinery. The purpose of the gear train is to transfer the power generated by the water wheel to three vertical shafts or spindles which turn the runner stone of each of three pairs of stones. The master gear (also called pit gear) is mounted directly on the same shaft as the water wheel by virtue of a retrofit square iron casting at the center of the wooden master gear. The master gear turns at 8 rpm, as does the water wheel, and turns clockwise as viewed from its front. The master gear is approximately 10 feet in diameter and has 78 hickory teeth. It was rebuilt from the original pattern in the 2002 time frame. The gear train is a counter shaft gearing system. The master gear drives a left counter shaft (corn) and a right counter shaft (wheat). The left counter shaft drives one stone, and the right countershaft drives two stones. The master gear meshes with two lantern gears called wallowers, one of which drives the left countershaft, one of which drives the right countershaft. The left wallower has 21 hickory rounds, the right wallower has 23 hickory rounds. The countershafts are engaged and disengaged using countershaft levers. Pushing the lever forward engages the countershaft, and pulling it back disengages the countershaft. When engaged, a wedge block is inserted behind the moveable countershaft bearing block to insure that the countershaft remains engaged. Due to the clockwise rotation of the master gear, there is an upward force on the left countershaft and a downward force on the right countershaft. For this reason, the left countershaft bearing block has a tenon which fits into a mortise in the hurst frame post as well as a handwheel which must be tightened to secure the countershaft in position (in addition to the wedge block). Since the force on the right countershaft is downward, neither a tenon nor a handwheel is required. Face gears on each countershaft convert the horizontal rotation of the countershaft to vertical rotation of the stone spindles. The face gears are approximately five (5) feet in diameter. The left countershaft face gear has 44 hickory teeth, and the right countershaft face gears have 36 hickory teeth. A pinion gear called a stone nut (or stone pinion) meshes with the face gear to drive the vertical spindle. Originally, the stone nuts were all lantern gears, but Mr. Collins replaced two of the three lantern gears by custom made cast iron gears. Each gear is lifted off a cast iron hub to disengage the spindle. Both cast iron gears have 14 teeth. Each spindle is hand forged wrought iron, and supports the entire weight of the runner stone above (3200 pounds in the case of the corn stone). It passes through the eye of the bedstone, which is stationary, and drives the runner stone which is positioned above the bedstone. The bottom of each spindle is supported by a steel bearing which is recessed in a cavity in the bridge tree called a tram pot. The bedstone is supported by the Hurst frame using two stone beams If the water wheel turns at 8 rpm, the corn spindle turns at 93 rpm and the wheat spindles turn at 70 rpm. At that speed, this mill would have produced about 1000 pounds of grist per hour. Tentering is the term applied to raising and lowering the runner stone to adjust the spacing between it and the bedstone which determines the fineness or coarseness of the grist. The bottle beam (also called a lighter staff or tentering staff) raises or lowers the spindle by minute amounts to accomplish this. A leather strap wrapped around the end of the bottle beam, secured by a bottle weight, keeps the bottle beam positioned exactly where the miller wants it set. The bottle beam leverages the brayer (beam) up or down which, in turn, moves the bridge tree (beam) up or down. The brayer supports the bridge tree which, in turn, supports the spindle. The miller has three mechanisms to control the milling process. One is the tentering adjustment described above; a second is the control of the flow of corn into the hopper using the crook peg. Turning the crook peg clockwise to tighten the leather strap raises the front end of the shoe and reduces the flow of corn into the hopper. The third mechanism is the flow of water out of the chute onto the wheel. A vertical gate control stick at the far left end of the hurst frame is connected to the control gate in the forebay. Raising the control stick reduces the flow, and lowering it increases the flow. Its position is fixed at the desired flow by positioning it on the dowel pin at the appropriate hole. |
Left Countershaft
Right Countershaft
|
|
1730 Conestoga Road, PO Box 42, Chester Springs, PA 19425 THE MILL | THE PEOPLE | THE TECHNOLOGY © 2010 The Mill at Anselma Preservation and Educational Trust, Inc. |
||
