Criteria for Selecting Drives for Trimmers and Instructions for Replacing Them

Grass mowing with trimmers occurs due to the use of a mowing head with fishing line and metal discs. Each type of cutting device has its own fundamental features. The use of fishing line is limited by the type of vegetation, therefore, where the head does not cope with the task, a metal disk is used. How to choose a cutting disc for the trimmer, what they are, and how to sharpen, we find out the details before buying the appropriate equipment.

What types of trimmer knives are

Initially, we note that metal discs can be used not only on gasoline, but also on electric trimmers. The main condition for the use of metal cutting knives on equipment is that the transmission mechanism (shaft or gear) must be of a rigid type in the design of the tool. A rigid type gearbox is a metal shaft that transmits torque from an electric or gasoline engine to a working body.

There are models of trimmers with flexible shafts, the design of the gearboxes in which is represented by a steel cable. These are, as a rule, low-power electric lawn mowers that are not designed for heavy loads, as well as domestic lawn mowers. Do not use metal discs on trimmers with a flexible shaft (you can only use plastic discs), as this will lead to a quick failure of the gearbox. Before buying metal cutting mills, you will need to find out the type of gear mechanism of your tool. rigid or flexible.

What type of gear is used on the trimmer is indicated in the datasheet for the tool. If the trimmer has a curved rod, then a flexible shaft is used in its design. Straight-bar tools can be equipped with rigid and flexible gearboxes, depending on the power of the trimmer.

Trimmer knives are classified according to the following criteria:

  • Material of manufacture. they are plastic and metal. Plastic knives are less effective than metal knives, however, they do not exert a large load on the shaft and tool drive mechanism. Plastic discs are used on household electric trimmers and lawn mowers.
  • Cutting device design. Steel disks come in two types. blade and gear (milling). Plastic knives are released in the form of blades. Toothed devices have a similar design with circular discs, and blade devices have large flat knives
  • Number of cutting edges. The number of teeth and knives on the discs is different, which affects the performance of cutting tools. On toothed discs, the number reaches 80 links, and on lobed discs. from one to four pieces
  • The presence of additional spraying. steel gear discs are additionally equipped with victorious soldering, which allows the use of tools for mowing grass on hilly surfaces. When the disk touches obstacles in the form of earth and stones, the teeth do not deform and do not blunt, which is achieved due to the presence of victorious solders. Specialists claim that carbide tipped devices do not last long. Soldering wears out quickly, and then the cutter is used without defeating
Read more:  Patriot Trimmer Won'T Start

Plastic knives for trimmers not only cost less than metal knives, but also do not exert high loads on the engine and gear mechanism. This is especially true when the knife runs into obstacles. The higher the elasticity of the cutting knife, the less likely it is to deform the plastic discs.

Advantages of trimmer discs compared to fishing line

The trimmer disc, in comparison with the cord, has its advantages. You need to know these advantages in order to ultimately decide whether to buy and use metal cutting knives. Consider all the advantages of trim discs:

  1. The ability to cope with different vegetation, unlike fishing line. It can be dead wood, long and thick-stemmed grass, and even small vegetation. The fishing line can hardly cope with medium-sized grass, and it is not able to cut thick-stemmed grass. The cord will either get tangled up in the grass, or the fishing line will wear out quickly, which is not rational
  2. High speed of achieving results. Unlike fishing line, the disk cuts grass qualitatively in one pass (with good sharpening), without leaving “cocks”, so mowing with a metal circle trimmer is faster than when using the cord
  3. Disks do not wear out, unlike a cord. Cutting knives or parts of the wheel are dull, but the issue is resolved by sharpening. How to sharpen a trimmer metal wheel is described in the material below. With prolonged use, the cutting devices wear out, but they last for at least 3-5 years
  4. Long service life unlike fishing line, which is associated with the design of equipment

Video: Criteria for Selecting Drives for Trimmers and Instructions for Replacing Them


There are also disadvantages of the considered cutting devices for trimmers. The first drawback is that you cannot work with a tool when cutting grass is carried out next to obstacles in the form of trees, buildings, stones, benches, etc. When a disk collides with an obstacle, the drive brakes, which is reflected in the form of such minuses:

Criteria for Selecting Drives for Trimmers and Instructions for Replacing Them
  • Engine overheats
  • Damaged blade parts that become dull
  • Transmission mechanisms fail. flexible and rigid shafts (gearbox)
Read more:  How to Start a Trimmer Petrol Carver

If you plan to mow thick grass in the field, then it is impossible to do without a trimmer with a metal disc installed. The fishing line is used for mowing small grass in private areas near obstacles.

Choosing the best cutter for lawn mowing

Some manufacturers of trimmers with a rigid transmission shaft design complete their tools with not only fishing lines, but also steel disks. This is not always the case, and if this situation is appropriate, then if necessary, instead of a mowing head with fishing line, a metal disk is installed. However, this is not always the case. First you need to make sure that you can use a steel disc on the trimmer. Consider all types and designs of cutting knives manufactured for trimmers.

Disc gear knife in which cases is used

Metal gear discs have the shape of a circle, at the base of which are located the corresponding number of teeth. These teeth come in many forms, shapes and sizes. The more teeth, the more efficient the tool is to cope with thick grass and even small trees. Milling wheels for trimmers gain speed faster, which is their advantage. They also have a high moment of inertia, which is their disadvantage. This negatively affects the drive unit of the tool, as the starting power increases, and as a result the motor overheats with frequent stops. In addition, the equipment differs in the presence and absence of perforation.

  1. Perforated circles with holes and a large number of teeth up to 40 teeth. effectively cope with mowing thick, tall and small, coarsened grass and shrubs. The larger the number of teeth, the less grass is ground. Grass is not wound around circles with many teeth. Discs with teeth in the amount of 60-80 pieces are intended for mowing grass with small trees available on the territory, the thickness of the stems of which does not exceed 7 cm
  2. Solid. disks that do not have holes in the structure. They have a lot of weight, so putting them on lawn mowers with an engine capacity of up to 30 cm3 is strongly not recommended. The tool simply cannot pull out the heavy cutting element. Compared with perforated, they weigh 1.5-2 times more. Effectively cope with dense and rare grass. The smaller the number of knives, the more grass is crushed, and the load on the motor increases. The load on the gearbox also depends on the angle of grinding of the teeth.
Read more:  Grass Trimmers Rating

If the operator is faced with the task of mowing thick grass and dead wood, it is recommended to choose discs with perforation and a large number of teeth. Solid discs are suitable for mowing green grass of different densities, but they are used exclusively on powerful lawn mowers with an engine capacity of more than 40 cm3.

Where are the blade knives suitable for trimmers?

Compared to gear or milling discs, blade blades are lightweight, therefore they are used on low-power trimmers. Bosch supplies its electric lawn mowers with just these types of cutting knives. Their advantage is in the minimum moment of inertia, which eliminates the negative impact on the drive mechanism.

The number of blades affects the grinding of grass. The smaller the blades, the more the mowed grass is crushed. For mowing homogeneous and homogeneous grass, two-bladed discs are used. Their dignity is that they throw away cut growths to the side. For mowing grass in the field when harvesting hay, it is recommended to use 4 or more blade nozzles. They do not crush the mowed grass, nor do they load the drive mechanism of the tool.

Plastic circles on the trimmer. when applied

If gas milling trimmers and metal blades are used, then it is recommended to use plastic circles for power tools. Their main advantage is low weight, so the load on the electric motor is completely excluded. Structurally, the nozzle is a plastic base on which knives are mounted around the perimeter. Knives are made of soft plastic, which, in contact with an obstacle, bends without deformation. The knives are mounted on a round base at an angle of 120 degrees.

They are designed to mow thick grass with electric trimmers when the line cannot cope. If the nozzle has a large moment of inertia, then it can be reduced by making symmetrical holes. When the teeth are blunted, they must be sharpened at an angle of 30 degrees using a grinding wheel with a low or medium roughness.