One of the most basic and oldest metal working
operation is shearing (also - machine metal shearing). Metal Shearing,
or Machine Metal Shearing, is defined as the mechanical cutting of
large sheets of metal into smaller pieces of predetermined sizes. A
metal shearing operation that completes an entire perimeter is known
as blanking, with the resulting work piece being called a blank.
Most metal shearing operations are accomplished by the
action of two blades, one fixed and one moving vertically, meeting
progressively from one side of the metal material to the other much
like ordinary hand shears. The angular alignment of the shear blades
is called the rake. Also to be considered is the blade or knife
clearance to each other. Both rake and clearance are a function of the
type and thickness of the material to be cut.
The “slip-plane” on the shear is the final cracking
from both the top and bottom of the work after the descending upper
blade partially cuts through the work. This upper blade is usually
inclined in relation to the bottom blade, 1/2 to 2-1/2 degrees. This
concentrates cutting pressure exactly at the juncture of the shear
blades and assures a cut exactly parallel to the blades. The slight
offset also helps clean material from between the blades.
Shearing is also done on a “shearing die” mounted in a
stamping press, however most metal shearing is accomplished with a
machine designed especially for the operation and is called a “shear.”
The typical shear consists of:
• a fixed bed to which one blade is attached
• a vertically moving crosshead which mounts on the
• a series of hold-down pins or feet which hold the
material in place while
the cutting occurs
• a gauging system, either front, back, or squaring
arm, to produce specific work piece sizes
Metal Shears may be operated manually, mechanically,
hydraulically, or pneumatically. They can also be classified by their
design. “Gap” and “gapless” metal shears are defined by their side
frames and the maximum size metal sheet they can handle.
“Right angle” shears have two shear blades set at a 90
degree angle to each other and will cut simultaneously in two
“CNC” shears are programmable to cut various sizes by
automatically feeding material into the blades.
“Ironworkers” are designed to cut angle and bar stock
and to perform punching operations. The sharpness of the knives or
blades critically determine the edge quality of the cut and the
accurate size of the work piece. Dull or improperly gapped or
positioned blades will create in the cut piece, either:
• a camber or deviation from a straight edge on the
drop side of the shear
• a bow which is the tendency of the sheared part to
arch in the center
• a twist which is the angular distortion of the part
from end to end
Another common shearing operation is known as
“slitting.” This operation begins with a master coil of a given width.
Material from the master coil is fed through a series of rotary knives
set to produce a group of more narrow stock widths for subsequent
Special thanks go
out to the Society of Manufacturing
Engineers for permission to use this text.