Many engineering components are produced from a sheet of metal, which is cut to shape and then folded to form the finished articles. The quickest and easy way to cut sheet metal is by shearing it. Cutting tools for sheet metal are also called shearing tools. Shearing tools which are operated by hand are known as hand operated shearing tools. Most commonly used hand operated shearing tools are as follows:
Snip (Hand Shear)
A snip is used like a pair of scissors to cut thin and soft metals. Light gauge sheet metals up to 20 SWG can be cut easily by using snips. These are available in many sizes up to 400mm in length. The longer handle gives greater leverage for cutting heavier gauge materials. The cutting angle of the blades of a snip is generally 80º. There are several types of snips available for making straight or circular cuts. Following are the basic types of snips:
(a) Straight Snips. These are also called tinman’s shear and have straight blades. These are used for making straight cuts and large external curves. These snips are very light and can be easily handled by one hand.
(b) Bend Snips. These snips have curved blades. These are useful for cutting small external and internal curves. These snips are also very light and can be easily handled by one hand.
(c) Universal Combination Snips. The blades are designed for universal cutting, i.e. straight lines or internal and external cutting of contours .These may be ‘right hand’ or ‘left hand. These can be identified easily, as the top blade is either on the right or on the left.
(d) Pipe Snips. These are used for trimming cylindrical or conical work in sheet metal. These have smaller and thinner blades than universal snips.
To produce the maximum cutting force, the hand must be as far as possible from the pivot and the metal being cut must be kept close to the pivot. The angle of the blade with the sheet metal should be about 18º to 20º.