Punches

Punches are used to punch holes in metal sheet, to locate centers for drawing circles, to start holes for drilling, to transfer location of holes in patterns and to remove damaged rivets and pins.

They are generally classified according to the shape of their points that are discussed below.

Center Punch: It is made of high carbon steel hardened and tempered. It has a point ground to an angle of 60^o and are is used to make large indentations in metal, which are necessary to start a twist drill. The titanium should not be centre punched as it sets up high internal stresses. Never use a center punch to remove objects from holes because the point of the punch will spread the object causing it to bind even more.

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Prick Punch: It is used to place reference marks on metal in order to transfer dimensions from a paper pattern directly on to the metal. To do this, first place the paper pattern directly on the metal. Then go over the outline with the punch, tapping it gently with a small hammer thus making slight indentations on the metal at the major points. These indentations serve as reference marks for cutting the metal. Never strike a heavy blow with the hammer as it may cause the prick punch to bend or cause major damage the work material.

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Pin Punch: It is used to drive the pin or bolt the rest of the way out of the hole. Stubborn pins may be started by placing a thin piece of scrap copper, brass or aluminium directly against the pin and striking it with a hammer until the pin begins to move. The parallel pin punch or drive punch is used to drive out rivets, bolts, split pins and shackle pins. The tapered punch or drift punch is used to deliver a blow to a part where access to a hammerhead would be difficult.

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Transfer Punch: It is usually 4 inches long and is used to transfer the location of holes through a template. It has a point that initially tapers, then runs straight for a short distance in order to fit the drill-locating hole.

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Hollow Punch: It is also known as hole punch and is used to make small holes in soft materials. The slot in the side allows the removal of the hole centres.

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Rivet Punch: It is used in the forming of snap-head rivets. These punches are also known as set-ups, snaps and dollies.

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