Attaching Knife To Trimmer

With the advent of summer, many owners of household plots are concerned about the issue of how to put a knife on a trimmer. No less relevant are the questions of why and when it is advisable to replace the fishing line on the lawn mow with a more durable cutting element. In our article we will try to make out all this and give useful recommendations to summer residents.

Why you need to put a knife on a trimmer

The trimmer with a knife mounted on it is most convenient to use for more comfortable mowing of tall and coarsened grass in the country. The line on the lawn mowing in such cases can not cope. Thin breaks very quickly. Using a thick 2.3 mm cord or homemade rods with cables causes the vegetation to wind up on the spool. This increases the load on the engine. As a result, the piston group and other moving parts of the unit wear out very quickly.

Attaching Knife To Trimmer

If the mowing of the weeds is carried out with an electric trimmer without a knife, only fishing line, even if it is thick with a curly section, the problem cannot be solved. There is always a risk of overheating the motor and damage the flexible shaft. And it’s all about the big torque of the electric motor. The grass wound on the spindle creates strong resistance to the shaft, resembling a speedometer cable, which does not withstand and twists.

In order to protect the equipment from premature wear, manufacturers have provided the ability to install special knives on trimmers. The design and shape of existing cutting elements makes it easy to cope not only with coarsened and overgrown grass, but also successfully deal with young shrubbery.

What knives to put on the electric and lawn mowers

Before buying and putting a knife on a lawn mow, we will find out what they are and in which cases they are used. Today, manufacturers offer consumers a large number of types of these consumables. In general, all cutting tools designed for mowing grass can be classified:

  • By the type of material from which it is made;
  • In the shape of its cutting blades.

The main material for making trimmer knives can be plastic or metal. The use of such consumables is largely dependent on two parameters:

For safety reasons, manufacturers do not recommend placing steel knives on electric trimmers. Almost all lawn mowers powered by mains and battery are equipped with plastic blades. Depending on the manufacturer, they can be of a single disc-shaped design with several blades or in the form of a special mowing head for the installation of removable plastic blades.

Straight bar at gas trimmer and curved at electric

To put a metal knife on an electric trimmer does not allow its design features.

  1. The curved rod of the unit reduces the distance from its working part to the legs of the mower. If the blades collide with a stone or other solid object, the braid is thrown to the feet.
  2. The high torque that we mentioned above, in the event of a collision of a metal knife with a solid object, transfers a large load to the flexible shaft of the trimmer and its motor. What causes their premature failure.
  3. The handle of an electric braid most often does not have a restrictive bar acting as a stop. Which does not exclude injury to the legs.

It is these features that allow the use of exclusively plastic knives on trimmers with electric motors. In a collision with an obstacle, the blades are destroyed, thereby protecting the legs of the mower from possible injuries.

Plastic knives cope well with overgrown and dry grass. They can mow nettles and stalks of burdocks.

The use of metal knives only on gas trimmers is also due to design features.

  1. The direct design of the bar increases the distance to the legs, which ensures complete safety.
  2. Convenient U-shaped and J-shaped handles allow to hold the tool firmly. D-shaped lawn mowers are equipped with a limiter resting on the leg of the pigtail, which does not allow the head to be pulled up to the legs when the cutting disc meets a solid obstacle.
  3. The clutch of the gasoline engine allows you to smoothly gain speed to the optimum level. And when the blade collides with a hard surface, it can absorb part of the impact.

Thus, gas trimmers with an installed metal knife are best used in large areas. They will successfully cope not only with tall coarse grass, weeds, burdocks and nettles, but also shrubs, as well as young trees.

The shape of the blade blades placed on the trimmer does not affect the quality of the work performed. Speed ​​does not depend on them either. Triangular, trapezoidal, rectangular shapes are all the marketing ploy of manufacturers.

If you plan to prepare hay, then it is best to put knives with a large number of blades on the lawn mower. Look for discs with eight teeth or discs with four large blades and four additional ones. Two and three blade knives will greatly chop the grass.

How to put the knife on the trimmer

Putting a knife on the trimmer is not so difficult. The manufacturer supplies his tools with a special pin that allows you to lock the gearbox and a key with which you can unscrew the spool with fishing line. The most important thing to observe when changing the cutting elements is the safety precautions and the assembly sequence of disassembly.

The algorithm for installing the knife on the trimmer is as follows:

  1. Remove the protective cover;
  2. We block the drive. To do this, combine two holes. in the shaft hub and in the gear cup. After combining them, insert the pin into the holes;
  3. We turn off the spool with fishing line or the fastening nut holding the boot (clockwise, if the trimmer has not been used) clockwise from the hub;
  4. Next, install the cutting knife, so that the slots on the hub washer coincide with the recesses in the hole of the cutting disc;
  5. Install the boot;
  6. We twist the fastening nut (counterclockwise) while holding the locking pin;
  7. Tighten it using a pipe wrench;
  8. Return the protective cover to its place.

As you can see, there is nothing complicated. Now you can safely proceed to mow the weeds on the site.

To mow tall hard grass or cut off wild growth of fruit trees, it is convenient to use a trimmer with a knife. Plastic knives are put on low-power electric trimmers, metal knives on more powerful gasoline ones. If you used to work with fishing line, the mowing head will need to be removed and a knife should be put in its place. Next, see detailed instructions on how to do this.

Video: Attaching Knife To Trimmer

Setting the knife on the trimmer

Before changing the knife on the trimmer, the tool must be turned off. If we are talking about lawn mowing. then turn off the engine.

Steps for installing the knife on the trimmer. instructions

  1. If the trimmer has not been used before. Fix a hex key in the gearbox hole (or a rod of a suitable diameter. this can be a regular nail). This is necessary so that the shaft does not spin. Loosen the fastening nut and remove the gearbox cup from the shaft.
  2. If a mowing head is installed. As in point 1, insert the key into the hole of the gearbox. Holding the key, unscrew the mowing head.
  3. Install the washer on the hub, then the knife. Make sure that the protrusions align with the notches. Then the knife will be correctly centered.
  4. Install the thrust washer and gear cup over the knife.
  5. Install the mounting nut on the shaft and tighten it counterclockwise. To do this, you will need a socket wrench.
  6. Please note. so that the nut does not loosen during operation, most gasoline trimmers have a stud that is inserted into the hole in the shaft.

Installing a knife on a trimmer. video

In conclusion, we suggest that you familiarize yourself with the video tutorial on replacing a knife on a Stihl gas trimmer. We remind you that the installation steps may vary slightly depending on the model. Therefore, do not forget to look at the instructions!

If the disc on the trimmer is used regularly, it needs to be removed from time to time and sharpened or replaced with a new one. This part can be made of metal or plastic, have a different number of blades, but the replacement process remains the same. over, this procedure is similar for technology from different manufacturers, whether it be Carver or Huter, but slight differences are possible. Changing the knife on the trimmer is quite simple if you follow the safety precautions and know the correct procedure, the description of which can be found in the user manual. The entire replacement process step by step, as well as the method of self-sharpening knives, will be described in this material.

When the use of knives is relevant

When using lawn mowers in suburban areas, the most popular nozzle is fishing line. It has a low price, suitable for different trimmer heads, safe to use. The disadvantage of using fishing line is that it is convenient only for mowing low growth. In other situations, the string immediately becomes clogged, regardless of whether a gasoline or electric trimmer model is used. In addition, vegetation is wound on the spindle, which creates significant resistance on the shaft and leads to its breakdown. It can also provoke a failure of the piston system in lawn mowers or a burnout of the motor in trimmers.

Therefore, for mowing tall or hard vegetation, various nozzles are used. So, for harvesting tall and rough grass, thin shoots of trees and shrubs, it is better to install and use a disk. This nozzle clogs much less often, which contributes to greater wear resistance of the equipment.

On a note! Due to the fact that the engine of trimmers and battery models is less powerful than on lawn mowers, so the use of discs is more relevant for gas mowers.

Features of lawn mowing discs

Knife disks are produced in plastic and metal, as well as in various shapes to perform diverse tasks.

  1. Two-, three- and four-blade Knives with pronounced blades are used for mowing grass and overgrown trees. However, they are not suitable for harvesting hay, as they chop the shoots by chopping them several times.
  2. Massive four-bladed discs are intended not only for clearing the ground from grass, but also for mowing hay. They prevent multiple cutting of the shoots, thereby making them suitable for harvesting for the winter.
  3. Perimeter Cutting Blades relevant for bevel reeds and reeds. Such knives are very heavy. this is a necessary quality to cut through thick stems.
  4. Professional saw tooth discs for brush cutters and lawn mowing, small trees and bushes can be cut.

As an alternative to metal discs, plastic knives are used. They do not need to be tightly mounted in the head, but they rotate as a result of centrifugal force. The durability of plastic knives is high, so the service life is quite long.

On a note! The advantage of plastic disks is that when they hit an insurmountable obstacle, they bounce off and there is no repeated contact.

Order of installation of a disk on the trimmer

Installing the knife on the trimmer is very simple. To do this, use the complete key that disconnects the cutting nozzle and the pin blocking the gearbox. The procedure is as follows.

  1. First of all, you should disconnect the electric trimmer from the network, gasoline. just drown. Detach and remove to one side the protective cover.
  2. Next, you need to combine the holes on the gearbox and shaft to insert a pin into them and lock the drive.
  3. If a spool with fishing line was used, it must be unscrewed clockwise.
  4. Then you need to find a nut to tighten the knife.
  5. The next step is to install the knives. Trimmers often wonder which side to put the disc on. This should be done so that the markings with numbers and letters are on top.
  6. Then you need to put the boot on top, and above it. the fixing nut, which must be tightly tightened with a wrench.
  7. The last step is to install the protective cover.

As you can see, the procedure is very simple and the same for many brands, whether it is the equipment of the company "Stihl" or Husqvarna.

On a note! If the owner of the device wants to replace the disk back with a fishing line, you can install a reel with it in the same way.

Disc Selection Criteria

You need to choose a plastic or metal knife, considering the area of ​​the plot to be processed, as well as the type of trimmer. electric or gasoline. The number of blades will depend on which shoots you need to remove with the tool. You can select the desired shape of the disk, the number of blades and the material of manufacture using the instruction manual of the device. Usually it prescribes which cutters it is recommended to use to solve certain problems.


It is not recommended to put metal knives on electric braids, since the design features make their use dangerous for the user. This is due to the curved shape of the rod, the lack of stops on the handles, as well as the high speed of rotation.

Important! The straight boom ensures safe use of the trimmer at times when the disc rotates against an obstacle. In this situation, it bounces back. towards the person, so a curved structure can cause injury.

Flexible Trimmers in terms of safety, plastic knives should be used. Their purpose is mowing soft grass, dead wood. While metal discs do an excellent job with tall, dense, hard shoots, shrubs, and also shoots of trees.


The number of blades is important in solving diverse problems. So, for chopping grass, two or three pieces are enough. For haymaking, it is necessary that the disk had from four to eight blades. To destroy small shoots of trees and shrubs, instead of lobes, there should be a large number of small teeth on the disks.

Disc sharpening

Regardless of the quality of the disc, over time it becomes dull and begins to cut grass poorly. If the knives are still relatively new, and replacement is not practical, you can sharpen them with your own hands.

Important! Only those discs on which there are no soldering from solid materials are suitable for sharpening. Such parts are thrown away, and new ones are acquired instead.

To sharpen disks, you must:

  • disassemble the trimmer, remove the knives;
  • carefully inspect the disk. if cracks are detected, it is better to replace the part with a new one, since its further operation is unsafe;
  • bent blades can be gently bent with a hammer;
  • given the size of the disk, you need to choose the right file for metal, this will provide more convenient work;
  • at an angle of 30 ° equally sharpen all the upper cutting edges of the disks;
  • reassemble the trimmer in the reverse order.

For sharpening the disc, you can use the emery machine at low speeds, setting up a grinding wheel with medium grain. Through such a tool, the process will move much faster. For safety, you need to wear gloves on your hands, and a face mask or glasses on your face.

So, for grass mowing on gasoline and trimmers, plastic and metal discs of various shapes and with a different set of blades are used. They are selected in accordance with the type of work performed and the size of the cultivated area. If the knives on the mower are dull, they are easy to sharpen or change yourself. Despite the simplicity of the procedure, you need to be careful and remember about safety so as not to be injured by negligence or damage the equipment. A more detailed description of the replacement of knives for a specific trimmer model can be found in the operating instructions or on the manufacturer’s official website. For clarity, the general scheme of the process is shown in the video.