In the majority of cutting rooms today, the cutting process makes use of hand shears, a mechanized knife blade in one of the several possible types, or a die press which stamps out the garment shape. Some of the methods currently in use are described below.
Hand shears are normally used when cutting only single or double plies. The lower blade of the shears passes under the plies, and some distortion of the fabric might occur which can be avoided with practice. Both left handed and right handed shears are available for left or right handed people. The major disadvantage of the method lies in the time it consumes and the consequent high labour cost per garment, but it is appropriate for made to measure garments.
A straight knife is used where the quantities for cutting do not justify purchase of a computer-controlled cutter. The elements of a straight knife consist of a base plate, usually on rollers for ease of movement, an upright or a standard carrying a straight, vertical blade with varying edge characteristics and an electric motor above it, a handle for the cutter to direct the blade, and a sharpening device. The base plate on its rollers slides under the glazed paper which is spread below the bottom ply of fabric in a lay. Normally, available blades heights vary from 10 cm to 33 cm and strokes vary from 2.5 cm to 4.5 cm. The greater the blade movement, the faster the blade cuts the fabric and the more rapidly and easily the operator can push the machine.
The straight knife is a common means of cutting lays in conventional cutting rooms because it is versatile, portable, cheaper than a band knife, more accurate on curves than a round knife and relatively reliable and easy to maintain. Even if a band knife is used for the main cutting operation, a straight knife would be used to separate the lay into sections for easier handling.
The elements of a round knife are a base plate, above which is mounted an electric motor, a handle for the cutter to direct the blade, and a circular blade rotating so that the leading edge cuts downwards into the fabric. Blade diameters vary from 6 cm to 20 cm. Round knives are not suitable for cutting curved lines in high lays because the blade does not strike all the plies simultaneously at the same point as a vertical point does. Therefore, a round knife is used only for straight lines or lower no of lays of relatively few plies.
Band KnifeA band knife comprises a series of three or more pulleys, powered by an electric motor, with a continuously rotating steel blade mounted on them. One edge of the blade is sharpened. The band knife passes through a slot in the cutting table in a fixed position and the section of the lay to be cut is moved past it.
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NotchersMany garments require that notches be cut into the edges of them to enable alignment during sewing with other garment parts. Specialized notching equipment provides greater accuracy because a guide lines up the notcher with the cut edge to give consistent depth of notch at a consistent right angle to the edge.
Drills and thread markers
Where reference marks are needed away from the edge of a garment part, such as for the position of the pockets, darts and similar features, a hole is often drilled through all the plies of fabric in the lay. The drill mounting includes a motor, a base plate with a hole to allow the drill to pass through, and a spirit level to ensure that the base is horizontal and hence the drill vertical. On many fabrics, the drill is used cold and the hole remains visible until the sewing operator comes to use it. On looser weave fabrics, where the hole may close up, a hot drill is used which will slightly scorch or fuse the edges of the hole. A hypodermic drill may be used which leaves a small deposit of paint on each ply of fabric. If it is important that no mark remains on the fabric, a long thread may be passed through the lay which is then cut with scissors between each ply, leaving a few centimeters visible on each garment panel. All drill holes must eventually be concealed by the construction of the garment.
Computer controlled cutting knives
This method provides the most accurate possible cutting, at high speed, and to keep the larger systems fully occupied they are frequently used in a central cutting facility that supplies a number of separate sewing factories. A typical computer cutting system has a table with a cutting surface consisting of nylon bristles which support the fabric lays but are flexible enough to permit penetration and movement of the knife blade which is supported only at the top. The bristles also allow the passage of air through the table to create a vacuum, reducing the height of the lay and holding it in place. The carriage supporting the cutting head has two synchronised servomotors, which drive it on tracks on the edges of the table. The cutting head contains a knife, automatic sharpener and a further servo motor which rotates the knife to position it at a tangent to the line of cut on curves. A sheet of airtight polyethylene covers the top of the lay, which assists the creation of a vacuum and allows significant compression of the lay. Control cabinet houses the computer and the electrical components required to drive the cutter, its carriage and the vacuum motor.
The spreader spreads the lay on a conventional cutting table equipped with air flotation. Paper is spread below the bottom ply so that the lay can be moved onto the cutting table without distortion and so that the bottom plies are supported during the cutting operation. This paper is perforated to enable the vacuum on the cutting table to operate to compress the lay. The cutting table does not need to be as long as the lay and its bristle surface can consist of a conveyor which assists in the transfer of the lay, in sections, from the spreading table and of the cut work onto the bundling tables.
Die CuttingDie cutting involves pressing of a rigid blade through the laid fabric. The die is a knife in the shape of the pattern periphery, including notches. Free standing dies generally fall into two categories. They can be of strip steel, manufactured by bending the strip to the shape required and welding the joint. These cannot be sharpened and must be replaced when worn. Alternatively, they can be heavier gauge, forged dies which can be re-sharpened but which are five times the price of strip steel. They provide a high standard of accuracy of cutting but, because of the cost of the dies, they are only appropriate to situations where large quantities of the same pattern will be cut. Die cutting also offers much faster cutting than knife cutting for the same depth of cut. It is proportionally more economic for small parts which have a greater periphery in relation to their area.
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