A new prototype escapement brings an unprecedented degree of accuracy to a Meccano clock.
The Riefler is known to be one of the most accurate mechanical clocks. It outrivaled both the Shortt free pendulum clock and the Le Roy clock and found a place in many of the astronomical observatories throughout the world before the advent of the atomic clock.
The Riefler owns its unprecedented degree of accuracy to the way in which the pendulum is supported and impulsed. Instead of the pendulum hanging as is usual from a fixed bracket, it is instead supported from a metal block which oscillates on knife edges. The block is directly rocked by the escape wheel. The result is that the pendulum is really impulsed through its suspension spring. the spring flexing at the just the moment to give maximum effect to the pendulum motion. Also the pendulum is able to unlock the escapement through the spring.
The Meccano Rielfer was originally built with a standard MW type 30 tooth escape wheel. There was no locking on each side, but rather the escape wheel was held up by the slope of each tooth before escape was allowed to occur by the action of the pendulum spring.
In the original Riefler, there were two separate escape wheels, one to give impulse, and the other to effect the locking. Each had a different type of impulse pin profile: a half round pin which was locked by the locking wheel, and the round pin which was moved by the impulse wheel after the method of Breguet. In actual practice, one wheel was closely positioned behind the other, and the impulse pin had two different profiles.
By arrangement with Stuart Borrill of Skegness, two escape wheels have been made according to the original design of Rielfer, and installed in the Meccano Riefler Clock. The new pallet pins replace the angle brackets. This arrangement can be seen in the picture (Fig. 1) where the two escape wheels positioned next to each other and the special pallet pins are held in the anchor.
Fig. 1 The new precision Riefler escape wheels and pallet pins
It should be noted that this is an unprecedented advance in accuracy for a Meccano Clock. Although the new parts are not Meccano, the arrangement of the new escapement shows to what degree of accuracy the Meccano system can support such delicate mechanisms.
Full instructions on the use of these special parts and availability will be published soon.
Michael Adler - November 2003