Post 604 –by Gautam Shah
Percussive tools deliver concentrated blows or impact. The delivery is in swift motion at specific location generating or transmitting a force. The tools can have ‘a nonspecific end’ or sharper point or edge as specific function end. The self weight of the impacting end delivers the mass, and the holding arm or the tool handle adds to the momentum while controlling the velocity. The ‘sharpness’ of the impact is determined by the type of task, which in turn is defined by the deformation required in the material. To beat flour dough or wet clay requires very little force, but to deform copper or iron greater impact is required.
The percussive hand tools operate on circular motion, where the handle or arm form a swinging arc to deliver the blow. In hand tools the length of an axis (radius) is formed by the combined measures of the handle and the operative arm. In case of machines, the handle is the ‘arm’. Percussive tools also use the pull of the gravity as a work force, such as for driving piles for foundation work.
Percussive tools have been of basic two types: The impacting ones with own head formations (axes pounder, beetle, mallet, maul, pestle, sledge, or with separate work points or edges. Percussive tools work as combination of head weight and handle length. Different combinations are used for craft to industrial work. Goldsmiths use light-head and long-armed hammers. A stone mason uses a heavy metal-head and small handle. For metal forging, the hammers have heavy-head and long-arm. A long handle, even if not needed for impact, it helps to control the blows reduces work fatigue. Soft headed percussive tools are used for sheet metal fabrication, painted elements, fabric levelling, etc.
HAMMERS: A hammer is a striking tool also known as a pounder, beetle, mallet, maul, pestle, sledge, etc. There are many trade specific hammers, like, the carpenter’s claw type, smith’s rivetting, boiler-maker’s, bricklayer’s, blacksmith’s, machinist’s ball peen and cross peen, goldsmiths’, smith’s stone (or spalling), prospecting, and tacks hammer. Each hammer has a distinctive form, with minor variations in terms of weight, length and angle of the handle, and the shape of the face. A pounder, or hammer stone, was the first tool to have a handle, marking a great technological advance. A long handle, even if not needed for dynamic effect (as in a tool used only for light blows), makes the tool easier to control and generally reduces operators’ fatigue. Club like pounders or mallet, with handles of the same material are widely used. The hammer as a tool, for nailing, rivetting, and smithing, originated in the Metal Age. For beating lumps of metal into strips and sheet, heavy and compact hammers with flat faces are needed, whereas lighter ones are more suited to rivetting and driving nails and wooden pegs.
Hammers with dual heads are in use since Roman age. Hammers with dual heads include: clawed hammers for pulling out nails, hammers with a chisel or pointed ends to dig out shafts, toothed edges to smoothen the stone surfaces. Other special forms of the peen (-the end opposite the flat face) like hemispherical, round-edged, and wedge like shapes helped the metalworker stretch and bend metal or the mason to chip or break stone or bricks. A file maker’s hammer has two chisel-like heads, to score flat pieces of lead (file blanks) that were subsequently hardened by heating and quenching. Heavy hammers are used as part of power tools, and largest are the pile drivers. Trip-hammers are gravity impulse based but steam hammers use, besides gravity a downward thrust from a steam-pushed piston. Pneumatic hammers driven by air include the hammer drill, used on rock and concrete. The rivetting hammer is used in steel construction with girders and plates.
Hammers’ heads are meant to impact the task pieces by striking over the head of a chisel, nails, shank, pins, bars, shaping dies, etc.
CHISELS: Chisels have been the chief cutting tools often combined with a hammering device. Chipped flints were used in 8000 BC, till neolithic period. Rectangular flint and obsidian chisels were used on soft stone and timber. Chisels with concave heads were used to create deeper sections. Chisels and gouges of very hard stone were used to dig out the bowls out of soft stones such as alabaster, gypsum, soapstone, and volcanic rock. The earliest copper and bronze chisels were long compared to flint chisels, and were used by the Egyptians to dress limestone and sandstone for their monuments. Use of wooden handles saved the chisel metal to half length, while causing less damage to the mallet. The chisel has since then taken on many shapes, and is being put to many different uses.
Modern day machines incorporate percussive processes. Forging workshops use automatic forging machines. Construction sites use pneumatic pile driving devices. Industrial presses use percussion as metal cutting, shaping, forming device. Stamping machine impact shaping or forming dies to generate a shaped product like coins. Gold foil makers beat small pieces of gold between layers of leathers.