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                                                                          Geometer describes the various types
                                                                          of springs encountered in the workshop

      HE SPRING    is an indispensable          Of the many different types of
       mechanical device based on            springs, two are really common in
       the property of materials to          regard to wide application-compres-
return to their original shape if            sion and tension (or extension). Both
not stressed beyond a certain limit.         are wound circular from wire or rod.
                                             The compression spring, E, has the
  Long exploited, this property is still     coils apart and is loaded in the direc-
not always perfectly understood. Early       tion of pushing them together. The
man made use of it in steadying his          tension spring, F, has the coils close
descent from a tree top on a resilient       together and is loaded to pull them
branch, or when projecting an arrow          apart. A compression spring is usually
from his bow. The pole lathe, the            finished each end by a slight closing
forerunner of machine tools, em-             of the coils, then grinding, so that the
ployed it in a springy sapling providing     last coil tapers off and the end is
the reverse run of cord wrapped round        substantially square. A tension spring
the workpiece.                               finishes in a small eye or loop, or
   Modern springs, in the restricted         with a hook each end.
sense of the term, are mostly of special        A flat spiral spring, G, made from
steels, hardened and tempered to             a long strip, is commonly called a
bestow resilience. All, however, work        clock spring-from long association
on one of two principles, or in com-         with spring clocks, other applications
plicated cases, a combination of the         being in watches, gramophone motors
two. These are by torsion, or by             and the carriages of typewriters. This
bending, or by a combination of both.        spring is housed in a circular casing
                                             and has a hook or hole at the outer
 Torsion springs                             end attached to the casing, and a hole
    A and B illustrate torsion. When a       at the centre end for a hook or pin
 bar is unstressed, the fibre or grain       on the shaft. Lubrication with light
 runs along it as a straight line. When      oil reduces friction.
 the ends are gripped and twisted in            A spring wound from wire or flat        one being in the cap of circular torches
 opposite directions, torsion is applied,    strip, circular and in the form of a       to maintain the batteries in contact.
 and the line is pulled round. On the        cone, is a volute spring, H. This has        A spring as at I from flat strip,
 torsion being released, the bar springs     various applications-a well-known          though often with longer legs, is
 back and the line straightens again.                                                   usually termed a lock spring-it being
 This is the principle of the torsion                                                   the type generally used, the eye
 bars employed on some car suspen-                                                      portion fitting over a pillar, one of
 sions; it is also that of small circular                                               the legs bearing against the body,
 coil springs.                                                                          the other against the levers or bolt.
    C and D show bending. In a flat                                                     A much heavier spring of the same
‘plate or leaf, there is supposed to be                                                 general form, but with a pin instead of
 a neutral line or plane along the centre.                                              an eye, is a gun spring-from use in
 On a load being applied, the metal on                                                  sporting gun breech and hammer
  one side of the neutral line is put in a                                              mechanisms.
 state of tension, or extended, while
 that on the other side is compressed.                                                  Leaf springs
 At the neutral line, there is, of course,                                                 The springs used on cars, when not
 neither tension nor compression. On                                                    torsion or coil pattern, are leaf type,
 the load being removed, the plate or                                                   J. In these, numbers and sizes of
 leaf springs back to its original shape.                                               leaves are settled according to re-
    On some springs combining the two                                                   sistance and resilience required. The
  means, it is not easy for an outsider                                                 top leaf with eyes for mounting is the
  to decide just how much torsion or                                                    main leaf. Others are assembled on
  bending there may be-since it would                                                   the centre bolt, and there are clips
  be quite possible to bend the bar at                                                  to hold them. In these springs, a
  B as well as twist it, and twist the                                                  certain degree of self-damping occurs
  plate at D as well as bend it-and                                                     from the friction of the leaves rubbing
  both would continue to function as                                                    together and lubrication with grease
  springs.                                                                              or oil is generally desirable.       q
 16 FEBRUARY 1956                                              261                                          MODEL    ENGINEER

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