Straight Knife Cutting Machine: Features, Parts, Uses & Advantages

Last Updated on 04/06/2021

Straight Knife Cutting Machine: Features, Parts, Structures, Uses, Advantages and Disadvantages

Saiful Sabuz
Department of Textile Engineering
Ahsanullah University of Science and Technology (AUST)
Email: saifulsabuz.tex23@gmail.com

Straight Knife Cutting machine:
Straight knife cutting machine is used to cut components of differing size. This is the most frequently used equipment for cutting garments in bulk. It is moved along the cut contours, while the fabric spread remains in a fixed position. The machines are manoeuvrable and capable of curvilinear cutting. Straight-knife cutting machine is the world’s most popular and most versatile. Available in all standard electrical configurations, with the largest variety of sizes and blade speeds in the industry. It is the most useful cutting instrument in garment cutting. In apparel industry, more than 99% cases this knife is used.

This machine is called straight knife cutting machine because its cutter is straight in shape. It is used for both woven and knit fabric. In this machine different types of straight knife are used according to the different cutting objects. This machine provides good efficiency. The maximum height of a cut spread is 300 mm. The weight of the machines varies between 5 and 20 kg. Heavier machines are less manoeuvrable. Small-capacity production units may use only straight-knife machines. It is widely used in Bangladeshi garment industry.

Features of Straight Knife Cutting machine:

The main parts of this machine are straight knife, electric motor, handle, grinder, base plate, stand/ knife holder, lubricating unit, wheel etc.
Could be used to cut higher depth of fabric.
Knife height is 10 cm to 33 cm.
Knife stroke is 2.5 cm to 4.5 cm.
Motor r.p.m. is 3000 to 4000.
Auto grinder is used.
Auto lubricating unit works for this machine.
Different types of knife edge are used for cutting different objects. Such as, straight edge, wave edge, sew edge and serrated edge.
A Handle for the cutter to direct the Knife.
Knife guard is attached to the front of the knife.
Sharp and heavy corners can be cut.
Maximum 70% of knife height is used for fabric lay.
Wheels are under the base plate to move the machine smoothly.
Machine weight is around 12-15 kg.
Knife cut the fabric very fast due to high speed of motor. That increases the risk of fabric damage.
Suitable for mass trimming cotton, woolen, linen leather and chemical fiber goods, etc.
Neat cutting, small-curvature radius curvilinear cutting.
Low noise, stable running, easy to operate and high efficiency.
Incorporated with an auto knife-grinding device, easier to operate.

Structure of Straight Knife Cutting Machine:
The straight knife cutting machine consists of a base plate, an upright stand to hold the vertical blade, motor, a handle for moving assembly, a sharpening device and a handle to transfer the whole assembly from one place to another.

Two kinds of power are required to operate a straight knife. Motor power drives the reciprocating blade and operator power drives the knife through the lay. Normally the available blade heights vary from 10 cm to 33 cm and normally available strokes vary from 2.5 to 4.5 cm. The greater the blade movement the faster the blade cuts the fabric and more easily the operator can move the machine.

The most important consideration is selecting a straight knife is the power required from the operator to move the knife is the power required for the operator to move the knife through the lay. Operator effort is affected by the weight of the motor, the shape of the stand, handle height, stroke, sharpness of blade and the base plate movement.

The normal blade has a straight edge that varies from coarse to fine depending upon the type of fabric being cut. Wavy edged knifes are used to reduce the heat generation and hence can be used for cutting synthetic materials without fusing difficulties. The speed of the blades can also be adjusted by having variable speed mechanism.

The straight knife is a common means of cutting lays in conventional cutting rooms because it is versatile, portable, chapter than a band knife and easy to maintain. Even if a band knife is used for main cutting operation, a straight knife will be used to separate the lay into sections for easier handling.

Different Parts of Straight Knife Cutting Machine
A straight knife machine has the following main parts (See the Figure-3):

Upper handle,
Electrical cable,
Motor,
Side handle,
Knife sharpener,
Stand,
Presser foot,
Straight knife, and
Base plate with rollers.

Straight knife:
The main functional part of the machine is a vertically oscillating straight knife with a sharp blade. In more powerful machines, the knife is longer, and higher spreads can be cut (80–300 mm). The width of the knives is between 10 and 20 mm and the thickness from 0.40 to 0.45 mm. The thickness of the knife is directly proportional to its length. Double-bevel knives with straight-edged blades are normally used to cut textile materials.

The cutting blades for straight knife cutting machine comes in three grades and also in several shapes as shown in Figure-4 for the cutting of unusual or difficult material.

straight knife cutting machine blades — Figure-4: Straight knife cutting machine blades

Knife sharpener:
It is small band with grinder/sharpening material on it and its main function is to sharpen the blade. It is necessary to stop the work process during the sharpening. The frequency of sharpening depends on the material being cut and on the knife blade.

Fabric presser foot
It is a device in the machine which holds the layers of the fabric tight so that it will easy for cutter to cut the fabric. A presser foot is used to ensure compression of the spread directly in front of the knife and to decrease displacement of fabric plies during cutting. It also prevents any loosening of the plies during the return movement of the knife. The height of the presser foot is changed according to the height of the spread.

Base plate and its rollers
A base plate with the lowest possible profile is needed to ensure the stability of the machine. This facilitates its manoeuver ability and minimizes the risk of deforming the material plies during the work process. Independently moving rollers are fixed under the base plate to ensure easy movement of the machine. Wheels are under the base plate to move the machine smoothly. Machine weight is around 12–15 kg.

Electric cable:
An electrical cable supplies the motor with electricity. During the cutting process, it must be secured away from the surface of the cutting table to avoid the possibility of electric shock.

Motor:
Motor rpm is 3000–4000 and its main function is to move the blade up and down and also slightly in front direction to create a stroke on fabric. Knife cuts the fabric very fast due to high speed of motor. That increases the risk of fabric damage.

Moving handle:
This handle is to hold the machine as well to move in predefined direction. The straight knife is a common means of cutting lays in conventional cutting rooms because it is versatile, portable, cheaper than a band knife and easy to maintain. Even if a band knife is used for main cutting operation, a straight knife will be used to separate the lay into sections for easier handling.

Safety devices:
A presser foot is used to compress the fabric plies and helps to protect operator’s hands from accidental cuts. A machine may be also equipped with an autostop trigger that switches the power off when the operator’s hand is removed from the lever. During cutting, the operator must wear special protective gloves (Figure-5). These are made from stainless steel chain mail and give a certain level of protection against stab wounds or cuts that could occur when the blade moves close to the operator’s hands.

cutting machine safety gloves — Figure-5: Cutting machine safety gloves

The gloves may be a universal size or of different sizes, fitting to either right or left hand and covering the whole hand or separate fingers. Unfortunately, the protective gloves are heavy and limit hand movement. Therefore, some operators may not use the gloves, putting themselves at risk of serious injury.

Advantages of Straight Knife Cutting Machine:

A large number of fabric lays can be cut by the machine due to high length of knife and r.p.m. of the motor. So, productivity is high.
Automatic grinding.
Automatically lubrication.
Comparatively cheap.
Can be moved easily by wheel.
Suitable for straight line and curve line.
Can be cut high curve line than round knife.
Fabric can be cut from any angle.

Disadvantages of Straight Knife Cutting Machine:

High speed of the machine causes high risk of damage.
Faulty knife could damage fabric layer.
Motor weight creates knife deflection which may be creates faulty pieces.
Risk is high for physical damage of operator.
Knife required to replace.

Uses/Application of Straight Knife Cutting Machine:
It’s suitable for straight line cutting, curve line cutting and for large part cutting. It is used for large production. Most commonly used in Garments Industry of Bangladesh (99%).

References:

Industrial Cutting of Textile Materials, 2nd Edition by Ineta Vilumsone-Nemes
Apparel Machinery and Equipments by R. Rathinamoorthy, R. Surjit
Apparel Manufacturing Technology by T. Karthik, P. Ganesan, D. Gopalakrishnan
Garment Manufacturing Technology by Rajkishore Nayak, Rajiv Padhye

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Mazharul Islam Kiron

Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. Mr. Kiron is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.