Bells could quite easily be swung between a series of beams spanning
the tower, and this has been done.
This arrangement is not ideal, in that the horizontal forces are taken
directly into the tower walls at bell bearing level.
The principle to be aimed at is to minimise the effect of the horizontal
forces on the tower structure.
This is achieved by the use of trusses, or frame sides, enclosing each
bell pit. These trusses are usually 'A' shaped, made of cast iron, steel
or timber, and supported from a double foundation of steel or hardwood
beams, with one level laid upon the other at 90°, and with the beam ends
securely anchored to all four walls.
The late Mr. E.H. Lewis, M.A., formerly Mechanical Science
Exhibitioner of Trinity College, Cambridge, conducted research and
experiments to expose the fallacy of the theory that elasticity in a bell
frame relieves the strain on the fabric of a bell tower, a theory that was
widely held at the time, and one which can still be met today.
A summary of his work was included in a book entitled "Bell Towers and
Bell Hanging, an appeal to Architects", by Sir Arthur Heywood, in 1914.
Although long out of print, it may be found in some reference library
He showed, by means of calculations and graphs, the magnitude of the
forces generated by a bell swinging through a full circle. For
simplicity, these forces may be resolved into their vertical and
horizontal components. The vertical force apprxoximates to 4¼ times the
deadweight of the bell and the horizontal force to 2½ times the deadweight
of the bell. The graph constructed from Mr. Lewis's figures shews these
forces plotted against time for one whole pull. The accompanying diagram
illustrates the interaction between bell and ringer for the same whole
pull. It will be seen that two horizontal maxima occur in each
revolution, in opposite directions, and the interval between them is
approximately ¼ of a second.
It will also be seen that considerable time is spent at the beginning
and end of each revolution when rotational movement is very slow, and it
is during this time that the ringer takes whatever action is necessary to
change his striking position. If he is 'moving out behind', he will be
striking one place later at each stroke, so he will let the bell rise a
little higher to allow the ringer of the bell he is changing with, to get
in front of him. If he is moving down to lead, he will be striking one
blow earlier each time and will check his rope to prevent his bell rising
so high. When dodging, he will let the bell rise at one stoke, and cut in
at the other.
It will be realised that while the bell is mouth upwards, near the
point of balance, movement in the frame or tower is likely to have an
adverse effect on the bell, because it could be thrown off balance one way
or another. This would not only make the bell more difficult to handle
because of the extra exertion required to control it, but the correct
timing and rhythm would be upset. Mr. Lewis established that tower
movement of as little as 1/32" (0.75mm) at the level of the bell bearings,
can start to have an adverse effect on the handling of bells.
This illustrates the desirability of making the tower and bell frame as
rigid as possible.
The ratio given for the horizontal force with respect with the bell
weight ONLY holds good where the frame and tower are rigid. If movement
occurs, the forces build up very considerably.
The bells should be arranged in the frame in such a way that the ropes
fall as close as possible to a circle in a clockwise direction with the
minimum drawing of ropes out of plumb. Normally, some bells swing
east-west and the remainder north-south. To establish the extent of the
horizontal forces in either direction, it is safest to total the weights
of all the bells swinging in that direction and multiply by 2½.