Unique Tower Clock Weight Safety Catch

Transcription

1 Unique Tower Clock Weight Safety Catch by Gerald P. Francis (VT) and Mark C. Thermansen (VT) Shelburne Farms is a National Historic Landmark Site in Shelburne, VT, on the northeastern shore of Lake Champlain. More than 125 years ago (about 1886) Dr. William Seward Webb and his wife, Lila Osgood Vanderbilt Webb, began the development of Shelburne Farms, which eventually grew to 3,800 acres by the turn of the century. Today the National Historic Landmark Site includes the central 1,400 acres of their original Shelburne Farms. Lila was the youngest daughter of William H. Vanderbilt (son of Commodore Cornelius Vanderbilt), and Dr. Webb was a prominent railroad executive, who led the development of America s railroads. They were married in 1881 and shortly afterward developed their first farm, Oakledge, in Burlington. In 1886 they moved six miles south to Shelburne and established Shelburne Farms. 1 In 1885 the Webbs added a #0 Hour Striking Howard Tower Clock (Figures 1 and 2) to the steeple on the horse stables at Oakledge Farm and later moved it to the new Farm Barn at Shelburne Farms around The central building of the Farm Barn was a 206 x 57, four-story building topped with a rectangular cupola designed to house the Howard clock from the Oakledge Farm (Figures 3 and 4). The new bell for the Farm Barn clock was cast by Meneely & Co. in West Troy, NY. The 36-1/2-inch-diameter bell weighed about 1,000 pounds. Its cast inscription said: This bell was hung in commemoration of the great Republican victory in the election of Gen. Benjamin F. Harrison, Nov. 6th, 1888 and was paid for by a disappointed Democrat. A near catastrophe was avoided because of a unique safety catch 2 that appears to have been made at the time the barn was constructed in 1888 or shortly thereafter. What led the farm staff at Shelburne Farms to invent this safety catch appears to be related to the clock s move from Oakledge to the Farm Barn at Shelburne Farms. Shelburne Farms 1885 Howard clock s bell wire rope failed on April 17, The 3/16 wire rope appears to have been the original. During the 2013 failure, the roughly 450 pounds of bell weights (Figure 5) were immediately caught by the safety catch (Figure 6) that is attached to the bottom of a wooden platform on which Figure 1, above #0 Howard Hour Striking Tower Clock with four dials at the Farm Barn, Shelburne Farms. Figure #0 Howard Hour Striking Tower Clock with four dials at the Farm Barn, Shelburne Farms. were mounted the original Howard square metal weights in an enclosed weight chute (Figure 7). The wings, four inch metal hooks, were caught on all four sides of the 11" x 11" wooden weight chute at the time the wire rope failed, as shown in Figure 7. The safety catch worked to stop the weights from falling from the attic above the fifth floor clock room in Shelburne s Farm Barn. The vertical weight chute is approximately 25 feet in height and terminates in a fixed NAWCC Watch & Clock Bulletin July/August

2 Figure 3. Farm Barn at Shelburne Farms, SHELBURNE FARMS ARCHIVES COLLECTION. Figure 4. Farm Barn at Shelburne Farms, PHOTO BY ORAH MOORE. SHELBURNE FARMS ARCHIVES COLLECTION. Figure 5. Ten 45-pound weights mounted on a wood platform supported by a rod attached to the wire rope block system. The Shelburne Farms safety catch is below the wood platform. Figure 6, below. Shelburne Farms bell weight safety catch free from the wood chute walls. The two diagonal leaf springs are in tension and held against the bottom of the wood platform when the wire rope is intact. Figure 7. Shelburne Farms bell weight safety catch engaged into chute walls at the wire rope failure on April 17, The two diagonal leaf springs are free. 324 July/August 2015 NAWCC Watch & Clock Bulletin

3 catch box on a catwalk high above the three-story storage and work area of the barn. It is doubtful if the catch box on the cantilever-supported catwalk would have prevented the weights from continuing down to the ground floor of the barn. This is a unique safety catch, because typical tower clock installations use a fixed catch box filled with stones on a firm foundation. The clock was moved to Shelburne 3 in 1888 by the Webbs from their much smaller farm in Burlington. The Oakledge installation was probably one for which the clock and bell weights had two-fall and four-fall suspension systems (Figure 8), respectively, with typical catch boxes. This assumption is based on the running block systems at the Farm Barn that appear to have been moved from Oakledge. These would have required about an 8-foot fall for the clock weights and a 10-foot fall for the bell weights if it was installed for a 7- or 8-day winding time. At Shelburne, the distance from the attic beam to the floor of the new clock room was about 12 feet. The weight chutes could have terminated with typical weight catch boxes supported by the clock room floor beams if the Oakledge installation was duplicated. However, the bell at Oakledge was a 250 pound McShane bell, which, when the clock was moved to Shelburne, was replaced with a 1,000 pound Meneely bell that William Webb won on a wager involving the election of Benjamin Harrison as president in The buildings at Oakledge were much smaller than the new buildings in Shelburne. The new bell could not be placed above the clock in the attic, so it was put below the clock level to the south in a fourth floor barn roof ventilator. This location for the Meneely bell required additional pulleys to activate the bell hammer. The increased frictional losses with the extra pulleys probably necessitated a change to a lower resistance three-fall suspension system with a longer chute. This chute extended below the clock room floor to a catwalk. Examination of the base of the bell weight chute termination on the suspended catwalk suggests that, without the unique safety catch, it would not hold a free fall of 450 pounds should a wire rope failure occur. The management personnel at Oakledge and Shelburne, under Webb s grounds manager, Archibald Taylor, probably designed this unique safety catch to protect workers in the expansive spaces below the catwalk catch. The safety catch uses the design concepts that Elisha Otis patented 4 for his brake elevator in the 1850s. The safety catch at Shelburne uses two leaf springs that are the diagonal pieces of metal seen in Figures 6 and 7. For the free catches in Figure 6, the springs are held against the wooden platform as shown on the drawing in Figure 9. A close-up of the springs in tension and held by the trip ring against the wooden platform is shown in Figure 10. If the wire rope fails, the weight support rod falls and the leaf springs become free and drive the trip ring down against the wing catches, which engage the chute walls as shown in Figure 7. This is illustrated in Figure 11. A close-up of the free spring pushing the trip ring against the wing catches is shown in Figure 12 The Shelburne Farms weight catch design has no ratchets as was the case for the elevator brake. Instead, the soft wood walls of the chute catch the pointed wing tips. The repairs to the bell weight system at the Farm Barn will use the original weight chute safety catch. New wire rope will replace the failed rope, and the double pulley from the four-fall suspension brought from Oakledge Figure 8. Weight fall suspension systems. Figure 9. Drawing of Shelburne Farms weight catch system in free mode. NAWCC Watch & Clock Bulletin July/August

4 Figure 10. Shelburne Farms weight catch system in free mode. will finally be replaced with a single pulley. The Oakledge bell weight running block was kept as a twin pulley system (Figure 13), when the four-fall weight suspension system was converted to a three-fall system 125 years ago. Otherwise, the repaired weight suspension is the same system that has provided protection for 125 years at Shelburne Farms. The Otis Patent drawing in Figure 14 has the side view on the left and the front view on the right. The front view shows the lifting rope fastened to the spring above the elevator car. The spring is in enough tension to keep the sprockets from engaging the wall ratchet bars. When the rope fails, the tension in the spring is released and the ratchets are immediately engaged. The Farm Barn is now the headquarters for Shelburne Farms as a nonprofit educational organization and includes administrative and teacher offices, the McClure Center for School Programs, a teaching Children s Farmyard, a farmhouse cheddar cheese production facility that uses milk from a 115 Brown Swiss herd, and independent partners, which include a wholesale organic bakery, a pair of custom wood furniture makers, and a co-educational, elementary day school that strongly focuses on outcome-based education. Acknowledgments The authors especially thank Wally Allen, Shelburne Farms buildings and grounds manager, who worked with them and without whom this unique safety catch would not have been understood. Wally oversaw the rigging Figure 11, above. Shelburne Farms weight catch system in engaged mode with the leaf springs free. Figure 12. Shelburne Farms weight catch system in engaged mode. Note the free leaf spring. Figure 13. The original dual pulley from Oakledge Farm operating at Shelburne Farms for 125 years using only one pulley after the conversion from a four-fall system to a three-fall system. 326 July/August 2015 NAWCC Watch & Clock Bulletin

5 and repairs of the bell weight suspension system that was completed on April 3, Notes 1. The farm is a National Historic Landmark Site with a specific mission: Educating for a Sustainable Future. 2. The term unique safety catch is used here, because there is no known device based on the authoritative treatise on Tower Clock Weights ( net/~donnl/cables.html) by Donn Haven Lathrop. 3. Tower Clocks at Shelburne Farms are discussed in Tower Talk, The Official Newsletter of NAW- CC Tower Clock Chapter 134, Issue 17, April The Otis elevator brake was built to suspend an elevator car safely in the shaft, if an elevator cable snapped. Otis started experimenting on how to make the brake by placing a wagon spring above the car. Then, he attached a ratchet bar to the guide rails on the sides of the elevator chute. The lifting rope was next fastened to the wagon spring, so that the weight of the car held just enough tension on the spring to keep it from touching the ratchet bars. However, if the rope failed, the tension would be released from the spring. It would then immediately engage the ratchets, preventing the platform from falling. A copy of the Otis Patent is in Figure 14. Figure 14. Otis Elevator Brake Patent No. 31,128. About the Authors Jerry Francis is professor emeritus of mechanical engineering at the University of Vermont, where he retired in 2000 after 40 years in higher education as administrator and professor at five universities. He has been involved with Shelburne Farms as a volunteer since 2004, giving tours and researching farm and family history and tower clock care. Mark Thermansen retired after 31 years with IBM Corp. He has been a volunteer at Shelburne Farms since 2004 and is involved with the spring lambing effort, property and breeding barn tours, and tower clock care. THE 2015 NAWCC WARD FRANCILLON TIME SYMPOSIUM Mechanical Music & Marvels October 22-24, 2015, in Houston, TX LOVE A GOOD MYSTERY? Do you like clocks filled with hidden surprises, say: birds, chimes, bells, whistles, movement, and music? Yea! We have that, and that, and that! To see these marvels and learn their history, join us at the 2015 Time Symposium. As a bonus, the Symposium will include tours of two large private collections. Hotel information Houston Marriot Westchase 2900 Briarpark Drive Houston, TX (713) Visit nawcc.org or check out the Watch & Clock Bulletin and Mart & Highlights Special NAWCC rate of $99 plus applicable taxes. Call hotel directly for NAWCC rate. for more info! NAWCC Watch & Clock Bulletin July/August