The lawn mower does not spin the knife


In the first case, work is organized if the blades are in relatively good condition and are only slightly dull. Usually, this sharpening is used if the owner sharpens the cutting elements of his garden tools several times per season. If this is the case, then it will be quite enough to walk along the edges with a file and correct them.

During work, the curvature of the knife, roughness are removed. It is important to maintain the factory-cut angles and descent. Both sides (blades) are grinded evenly. The sharpener is kept in the same position. Imbalance must not be allowed, in which case the well-coordinated work of the blades cannot be achieved. Such a problem will lead to operational wear of assembly units (bearings).

After the main sharpening, it is necessary to edit the edges. This is done in order to remove the smallest breakages. It is best to use 800 grit sandpaper. Editing consists in slightly shifting the paper along the plane of the descents.

Note! Instead of a file, you can use a sanding stone. Before the procedure, it is soaked in soap and water for a quarter of an hour. During operation, it is also allowed to slightly moisten the tool.

The mower does not cut the grass

There are two possible options here.

  • The knife is blunt or broken. Sharpen it with a file, an angle grinder, on a grinder (you need a flat-cylindrical grindstone) or on a machine (or drill) with emery wheels. Check torch balance.
  • The cutter itself is not set correctly. Set a gap in the cylindrical mower between the rotating cylinder and the blades of the knife equal to the thickness of the sheet of paper.
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Lawn mower knives: requirements, varieties, mounting features and selection

A knife is no less popular than a fishing line or cord, a working tool for a lawn mower. If in the trimmer you can do with fishing line or cord, then the knife is basically a cutter for lawn mowers, the power of which is noticeably more than that of trimmers.


A balance check is performed before installing the knife on the garden equipment. It aims to find out whether the blades of a knife have the same weight. To do this, a sharp strip is put on a pencil with a central hole. The shoulders should be balanced and equal in weight. If one of the sides pulls down, then grind it down a little again.

Reasons for removing the knife

Common reasons for removing or replacing a cutting element are as follows:

  • The knife is dull;
  • The element is bent and deformed;
  • Chips and cracks are visible on the knife;
  • The blade has worn off and thinned.

When the knife is dull, bent or deformed, the lawn looks untidy after mowing. Competent sharpening will correct the situation.

Professionals advise to carry out the procedure once a year. It is better to do this in the spring, before starting work. If the cutting elements become blunt faster, then sharpen them more often.

Knife sharpener

Lawn Mower Blades Will Not Spin. Blade Spindle Assembly Replacement

If chips, cracks are visible on the blades, or it has sharply worn off and become thin, then replacement is necessary in this case. There is no point in sharpening such a tool. In addition, the blade can break at any time and fly out from under the machine body, injuring people or animals that are nearby. Such a device can also damage the engine. It is allowed to change an element to a similar model. The characteristics of the knife are indicated in the instructions.

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Sharpening the blades

After preliminary straightening of the cutting part, you can start sharpening the lawn mower knife. Care must be taken to remove all chips, nicks, and deformed areas from the cutting edge and to ensure that the cutting edge slope is a single flat plane. For this, it is recommended to work slowly and carefully.

The emery bar is the simplest and most affordable tool when sharpening lawn mower knives. It is recommended to use a grinding stone with a grit of 400 to 600 grit. Before use, the bar is kept in soapy water for 10-15 minutes and during the sharpening process the grinding surface is periodically moistened with water or a weak solution of edible salt.

When sharpening lawn mower knives, it is important to keep the stone in the same position, otherwise there is a risk of knocking and making the cutting edge uneven. It is important to ensure that an equal amount of metal is removed along the entire length of the knife, otherwise the balance will be displayed incorrectly. An exception to the rule is a lawn mower knife with four blades: due to the number of working elements, such parts are insensitive to imbalance.

Lawnmower knife functions

The lawn mower blade performs the function of mowing grass. Knives are made of high quality steel. The sharpening of the knife affects the performance of the work. The sharp tool cuts plants evenly. Blunt. leaves a fringe on them, that is, a cut of each blade of grass is cut perpendicular to the surface into several parts. This happens if you tear the grass with your hands. As a result, the cut of the grass cut neatly and evenly is delayed the very next day. Such a lawn looks attractive and bright. In the second case, the area in front of the house turns out to be a dirty green color. The dissected sections are tightened only after 10-18 days.

Lawn mower knife

Note! An additional function of the blade in the lawnmower is to create an air flow during rotation, through which the plants are transferred to the grass catcher. For this, the blades often have several special serifs.

How to do it yourself

Overly thinned blades need to be replaced, but there is no need to buy factory-made pruning shears. you can make your own blades and replace them as needed. Homemade knives can be more expensive than factory knives, but having them will help save time spent on repairing the lawn mower.

Making homemade knives requires tool steel. Strips 3 mm thick and 20-50 mm wide are best suited. If the surface of the lawn is uneven and the soil is stony, then it is recommended to take thicker blanks. In this case, it is necessary to take into account the fragility of the material and its resistance to fracture. Unsuitable blades can damage the machine if broken.

The simplest version of a lawn mower blade looks like a long strip of steel attached symmetrically to the tool axis. In this case, you need to take a blank 30-50 cm long.

There is a second common option. two short homemade knives 50-80 mm in length, attached along the edges of the axis. It is important that the angle between them is exactly 180 ° to maintain balance and symmetry. Such blades are located both straight and with a slight inclination relative to each other. Blades are attached with one or two bolts.

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Regardless of the selected variant of the workpiece, you need to sharpen and balance.

The above techniques are only suitable for machines with steel blades. It is problematic to straighten plastic trimmer knives at home. In the event of a breakdown of such a unit, you must contact the service center.

Purpose and requirements

The purpose of the mower cutter is to cut the grass evenly and neatly in large quantities. In one session, when mowing one hundred square meters of a plot, you can collect tens of kilograms of grass. If the lawn mower has the function of shredding (mulching), such a knife should also chop the grass. The mower‘s cutter is designed so that its blades create upward thrust for the grass that has just been cut. She carries this herb into the collector.

The best alloy for a mowing knife is stainless steel. over, it must have a hardness of at least 55 units on the Rockwell scale. A lower hardness value will quickly dull the cutter. especially when cutting weeds and trimming bushes. Since the cut grass contains not only moisture, but also other active components, ordinary steel would quickly become covered with a brown coating after the very first mowing session. Stainless steel, creating on its surface a chromium oxide that resists corrosion (chromium is also included in the list of alloying additives), does not allow the knife to rust.

Important! In addition to being tough, the cutter must also be strong. If, during work, he stumbles upon a stone, then it should not fly apart.

How to fix and replace?

The knife should be changed every quarter or during the growing season, although sometimes it should be changed sooner. The installation of the knife is as follows:

  • if the mower is in operation, suspend it; for electric braids, it is enough to turn off the power (cord from the outlet, disconnect the battery); lawn mowers are disconnected from the key, unused fuel is drained back into the canister;
  • turn the mower to one side and remove the grass catcher;
  • clean off the ground and grass adhering to the working parts from the knife and the protective visor;
  • remove the visor (protective cover) of the knife; it holds back the grass scattered in all directions (when mowing);
  • unscrew the mounting bolt using a wrench or a head, the knife should not turn, it itself is attached to the adapter; it is recommended to wear work gloves before removing the knife so as not to cut yourself;
  • insert a new (preferably exactly the same) knife and tighten the bolt tighter, when it is loosened, the machine vibrates, or the blade itself may fly off.

If vibrations appear, but there is no replacement knife, it is necessary to balance the old one. Remove the knife and check its balance by hanging it on a screwdriver or nail with a large head. For this, the working part of the screwdriver is threaded through the central hole of the cutter itself. If there is an imbalance. one particular point will tilt, in this case, grind off a little metal. With repeated sharpening, the mass of the point that outweighs the others will decrease, and the center of mass will shift to its place. When balancing is complete, reattach the adapter and tighten the modified torch. If the adapter has a key holding it on the motor (gearbox) shaft. do not forget to press it into place.

If you find a previously purchased replacement cutter, install it immediately. In some cases, the holder also wears out. it needs to be replaced.

Selection Tips

First of all, the knife must be strong and durable. The best material for knives is stainless steel of the correct thickness, and not, for example, black steel with a spray of stainless steel or galvanized iron. Sometimes manufacturers indicate the grade of stainless steel, for example, AISI 304. The knife is not a part that is worth saving on.

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For portable lawn mowers, the minimum solution is a two-knife blade. In other words, you should choose a knife with two cutting edges. He will cut the grass. but he will not chop it up. To mulch the grass, buy an eight-pointed cutter. The optimum sharpening angle is approximately 30 degrees. You will quickly learn to recognize such knives.

The thread of the rotor pins, on which the cutter is put on with its mounting holes, does not matter. Usually it is left, if the knife turns to the right. and vice versa. This helps to avoid loosening the nuts and the knife coming off at full speed.

If your choice nevertheless fell on plastic knives, look for unbreakable and rather hard plastic that retains the factory sharpness of the cutting edge longer. This one does not fly apart in crumbs from the slightest impact when carrying or rolling the lawn mower to the place where the grass starts mowing.

Popular manufacturers

Both lawn mowers and accessories for them, for example, knives, are produced by popular manufacturers, the best of which are the following:

  • Bosch;
  • Gardena;
  • Craftsman;
  • Champion;
  • Makita;
  • Hyundai;
  • Daewoo;
  • Honda;
  • “Bison”;
  • Interskol;
  • “Anchor”.

Common breakdowns

Most often, the malfunctions are as follows: the mower does not cut the grass or does not turn on at all.

What should be the sharpening angle?

Lawn mower cutters are always sharpened at a 30-degree angle. A smaller angle will make the blade too thin, like a razor rapier. it will quickly serrate, bend, it can only mow short grass. Weeds and bushes are guaranteed to “ruffle” the edge. Too large an angle will lead to the fact that the knife will hit and break bushes more, tear the stalks of grass. than cut off both. In addition, the point should be sharpened on one side. and only slightly, barely noticeably sharpened from the opposite.

Blade and adapter shapes

If it is a simple blade cutter, then there can be several blades. but no more than 8. The shape of the blades of such knives can be as follows:

  • simple (in the form of rectangular ends);
  • rounded (extreme edges have a smooth curvature);
  • pointed (in the form of a wide dihedral bayonet).

Bladeless knives. a cutter that resembles a circular saw for wood. These knives are also called disc knives. The number of teeth is up to tens. They vaguely resemble a bicycle sprocket, the teeth of which have been sharply sharpened and changed the direction of the cut. There is a special type of cutter, in which the cutting part is not star-shaped, but stepped. It resembles rounded and curved steps, also evenly spaced. Their sheer parts are sharply sharpened. The height of the teeth or “steps” reaches several tens of millimeters.

The adapter is a two-blade knife adapter that fits onto the motor shaft. From the side of the knife, it has retaining rods threaded through the holes of the cutter itself. The whole structure is tightened with a central bolt. Simply put, an adapter is a knife holder. On the reverse side, it has toothed grooves that coincide with the teeth of the shaft. Matches according to the inner diameter of the central hole of the knife (for example, 22 mm).