_CRANK-HAMMERS._
Power-hammers operated by crank motion, adapted to the lighter
kinds of work, are now commonly met with in the forging-shops
of engineering establishments. They are usually of very simple
construction, and I will mention only two points in regard to such
hammers, which might be overlooked by an apprentice in examining
them.
The faces of the dies remain parallel, no matter how large the
piece may be that is operated upon, while with a trip-hammer,
the top die moves in an arc described from the trunnions of the
helve, and the faces of the dies can only be parallel when in one
position, or when operating on pieces of a certain depth. This
feature of parallel movement with the dies of crank-hammers is
of great importance on some kinds of work, and especially so for
machine-forgings where the size or depth of the work is continually
being varied.
A second point to be noticed in hammers of this class is the
nature of the connection with the driving power. In all cases
there will be found an equivalent for the elastic helve of the
trip-hammer--either air cylinders, deflecting springs, or other
yielding attachments,--interposed between the crank and the
hammer-head, also a slipping frictional belt or frictional clutches
for driving, as in the case of trip-hammers.