Hammer Springs
In the March 2009 issue of Clocks Ian Beilby describes making a replacement hammer spring for a countwheel longcase movement. He has made a spring of the type used from the late 18th century to the 19th century, particularly on provincial clocks. Earlier there were several other arrangements and The Longcase Clock Reference Book devotes seven pages to this important, but often misunderstood topic. Ian's movement is early 18th century and probably made in London, where the L-shaped hammer spring was rarely used. The spring should have been a flat blade that presses against the outside of the vertical bar at the rear of the hammer arbor (clearly seen in figure 5). When the hammer is drawn back the spring presses against to top part of this bar to give the striking force. The longer lower part then acts as a stop and moves the hammer off the bell to prevent jangling. It is clear that the end of the spring has been broken off, so it has been bent and moved to act on the other side below the arbor and a stop pin added.
It is very important when replacing parts that the correct type is fitted and adequate research is done to establish the correct function. The photograph shows the correct arrangement on a clock by John Selwood of Abingdon.
There are a couple of other contentious points. He states: 'The pivots must be parallel.' Ideally yes, but in practice no. I have seen movements that have had no bushing and with little wear, but have a noticeable taper on the pivots. This may have been done deliberately to provide self-centring so keeping the arbor shoulders clear of the plates. Also only in cases of extreme wear is it necessary to rebush hammer pivot holes. The pressure is only one way and as long as the wear has not moved the arbor so that the hammer does not function correctly (unlikely, especially with the spring arrangement described here), then an elongated hole is going to cause few problem.
John Robey, UK
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