Dorrin K Mace, Horologost

Dorrin K Mace, Horologost
The Clock Man in a pensive moment

Tuesday, October 11, 2011

What is a Grandfather/Long case/Tall case clock

A long case clock, tall case clock, floor clock or grandfather clock, is a tall, freestanding, weight-driven pendulum clock with the pendulum held inside the tower, or waist of the case. Clocks of this style are commonly 1.8–2.4 meters (6–8 feet) tall. The case often features elaborately carved ornamentation on the hood, or bonnet, which surrounds and frames the dial, or clock face. The English clockmaker William Clement is credited with the development of this form in 1670. Most long case clocks are striking clocks, which means they sound the time on each hour or fraction of an hour.
The terms "grandfather", "grandmother", and "granddaughter" have all been applied to longcase clocks. Although there is no specifically defined difference among these terms, the general consensus seems to be that a clock smaller than 1.5 m (5 ft) is a granddaughter; over 1.5 m (5 ft) is a grandmother; and over 1.8 m (6 ft) is a grandfather.
The advent of the long case clock is due to the invention of the anchor escapement mechanism around 1670. Prior to that, pendulum clock movements used an older verge escapement mechanism, which required very wide pendulum swings of about 80-100°. Long pendulums with such wide swings could not be fitted within a case, so most freestanding clocks had short pendulums. The anchor mechanism reduced the pendulum's swing to around 4° to 6°, allowing clock makers to use longer pendulums, which had slower "beats". These needed less power to keep going, caused less friction and wear in the movement, and were more accurate. Most long case clocks use a seconds pendulum(also called a "Royal" pendulum) meaning that each swing takes one second. These are about a meter (39 inches) long (to the center of the bob), requiring a long narrow case. The long narrow case actually predated the anchor clock by a few decades, appearing in clocks in 1660 to allow a long drop for the powering weights. However, once the seconds pendulum began to be used, this long weight case proved perfect to house it as well.
Modern long case clocks use a more accurate variation of the anchor escapement called the deadbeat or Graham escapement.
Traditionally, long case clocks were made with two types of movement: eight-day and one-day (30-hour) movements. A clock with an eight-day movement required winding only once a week, while generally less expensive 30-hour clocks had to be wound every day. Eight-day clocks are often driven by two weights – one driving the pendulum and the other the striking mechanism, which usually consisted of a bell or chimes. Such movements usually have two keyholes on either side of the dial to wind each one. By contrast, 30-hour clocks often had a single weight to drive both the timekeeping and striking mechanisms. Some 30-hour clocks were made with false keyholes, for customers who wished that guests to their home would think that the household was able to afford the more expensive eight-day clock. All modern striking long case clocks have eight-day movements. Most long case clocks are cable-driven, meaning that the weights are suspended by cables. If the cable was attached directly to the weight, the load would cause rotation and untwist the cable strands, so the cable wraps around a pulley mounted to the top of each weight. The mechanical advantage of this arrangement also doubles the running time allowed by a given weight drop.
Cable clocks are wound by inserting a special crank (called a "key") into holes in the clock's face and turning it. Others, however, are chain-driven, meaning that the weights are suspended by chains that wrap around gears in the clock's mechanism, with the other end of the chain hanging down next to the weight. To wind a chain-driven longcase clock, one pulls on the end of each chain, lifting the weights until the weights come up to just under the clock's face.
In the early 20th century,quarter-hour chime sequences were added to longcase clocks. At the top of each hour, the full chime sequence sounds, immediately followed by the hour strike. At 15 minutes after each hour, 1/4 of the chime sequence plays, at the bottom of each hour, half of the chime sequence plays, and at 15 minutes before each hour, 3/4 of the chime sequence plays. The chime tune used in almost all long case clock if the 4/4 Westminster Melody. Many also offer the option of Whittington Chimes or St Michael's Chime, selectable by a switch mounted on the right side of the dial, which also allows one to silence the chimes if desired. As a result of adding chime sequences, all modern mechanical long case clocks have three weights instead of just two. The left weight provides power for the hour strike, the middle weight provides power for the clock's pendulum and general timekeeping functions, while the right weight provides power for the quarter-hour chime sequences.

No comments:

Post a Comment

Note: Only a member of this blog may post a comment.