Over time and use, the lawnmower blade can lose its edge and become blunt. After years of honorable service, this tool's rotating blades may become less effective. You can see the effects of this phenomenon on the quality of the cut: the grass is torn rather than cut, the lawn takes on an irregular appearance and becomes more susceptible to disease. Fortunately, unless the blade is badly damaged, you can sharpen it with a few simple tools and a little elbow grease.
Steps
Part 1 of 3: Preparation
Step 1. Before proceeding, disconnect the spark plug
- You could be seriously injured if the lawnmower suddenly starts up again during maintenance. Although rare, lawnmower accidents require hospitalization and, in some cases, even surgery. For all these reasons, safety must be your top priority. To avoid any nasty surprises, first unplug the spark plug.
- To do this, usually, just detach the cable that protrudes on the side or top of the machine from its metal support. Once the cable is disconnected, the mower will not be able to start.
- However, it is highly recommended that you wear protective quanta and safety goggles during this type of work, even if you are more than sure you have pulled the spark plug out.
Step 2. Place the machine on its side with the carburetor facing up
- To access the blades, you need to tilt the mower. However, due to the construction system of these motor machines, the operation causes unpredictable transfers of oil into the carburetor and air filter. To prevent this from happening, remember to tilt the mower on the specific side so that these elements are facing upwards and not downwards.
- On modern machines, the carburetor and air filter are usually placed in a plastic casing on one side of the body. If you have any doubts about how your model is assembled, consult the user and maintenance manual or contact the manufacturer.
Step 3. Draw an identification mark on the underside of the blade
- One of the most common mistakes made by those who are preparing for this type of maintenance is to reassemble the blades in reverse. If this happens, know that the blade will not be able to cut the grass, no matter how sharp it is. To avoid the extra work of disassembling and reassembling the blades a second time, it is worth making a noticeable mark before proceeding with the next steps.
- There are many ways to recognize the underside of the blade. You can draw a dot of color with spray paint, write your initials with a wax marker, or stick a piece of masking tape in the center of the blade itself.
Step 4. Lock the blade and loosen the clamp bolt
- Most lawnmower blades are fixed in the center with a bolt. It is generally not easy to unscrew this bolt with a wrench or socket, because the blade rotates with the tool. For this reason you have to lock the rotating blade before unscrewing the bolt.
- Again, there are many ways to proceed. One of the simplest methods is to insert a sturdy block of wood between the blade and the body of the mower, so as to block rotation while loosening the nut or bolt. If it is more convenient for you, you can also use a vise or a jaw.
Step 5. Clean the blade of grass clippings and rust
- Once the blade has been immobilized, it shouldn't be difficult to loosen the center nut and take the blade apart. At this point, take the opportunity to clean it; if you have used the mower often, there will be a lot of dirt, grass and other dirt.
- For routine cleaning, all you need is a dry rag or a pair of gloves. However, if it has been a long time since you last cleaned the tool, you will need a little soapy water to remove the accumulated plant material and dirt. If so, remember to dry the blade thoroughly with a rag when you're done.
Part 2 of 3: Sharpening
By hand
Step 1. Lock the blade in a vise securely on your work table
- Take a sturdy vise or jaw and secure the blade inside it in the most comfortable position to work. For example, you can insert it so that the edge of the blade protrudes beyond the edge of the work table, more or less at the height of your waist, so you can sharpen it while sitting.
- It would be advisable to place newspaper sheets on the ground and on the table to collect the metal filings and make cleaning easier.
Step 2. Sharpen the blade with a file
- Run the file over the cutting edge. Direct the blows from the inner edge of the blade outwards until the metal becomes shiny and clean.
- Then, turn the blade and repeat the process on the other edge.
- The amount of metal dust you produce with this manual operation is much lower than that generated by other mechanical jobs. However, it is always wise to wear a mask or respirator to protect your lungs from airborne dust and metal particles, just as you would for large grinding projects.
Step 3. Follow the angle of the factory bevel as you proceed with the sharpening
- Hold the file at the same angle as the blade bevel as you work. Often, this angle is around 40 ° -45 °, although this is not a fixed rule. For this reason, check the instruction manual of your model to know the exact inclination.
- Ideally, once the job is done, the blade should be as sharp as a butter knife. In fact, lawnmower blades don't have to be sharp as razors; their rotation speed is sufficient for cutting.
Step 4. Once sharpened, remount the blade
- Spray some WD-40 (or similar lubricant) on the main nut, to make sure it doesn't rust, then insert the blade followed by the washers and then the main bolt. Finally tighten the bolt.
- Check that the blade is oriented correctly as you mount it; it shouldn't be a big problem, if you have drawn an identification mark on the lower face of the piece, as recommended at the beginning of this tutorial. The cutting edge should be facing the direction of rotation and / or towards the grass collection basket.
- Do not use the hammer to tighten the bolt. Most of the time, a good squeeze with a wrench or socket is sufficient. You should be able to feel how tight the bolt is through the resistance of the key.
With a Machine Tool
Step 1. When working with electrical machinery, obey common sense safety rules
If you're not already wearing eye protection, gloves, and long-sleeved dresses, now is the time to do it. Bench grinders and other sharpening machines can throw small sparks and thin metal splinters into the air at very high speed. These turn into "bullets" which can become very dangerous if you don't wear the proper protection
Step 2. Use a bench edger
- If you do not want to sharpen the blade by hand with the help of a file or there are imperfections or dents that you cannot eliminate, you have to rely on a machine tool. To sharpen the blades of common lawnmowers, a bench grinder is just fine.
- To do the work, move the cutting edge back and forth against the edger wheel. Just like for manual sharpening, you must keep the original angle of the bevel.
Step 3. Alternatively, use a belt grinder
- This is also a very common solution for blunt blades. The principle is always the same: make sure that the abrasive element comes into contact with the edge of the blade, so that the friction gradually sharpens it.
- To use a belt grinder, you have to turn it over so that the belt is facing up. You also need to lock the ignition trigger in the "on" position.
Step 4. Wet the blade to prevent it from overheating
- The strong friction that is created using a machine to sharpen the lawnmower blade makes the latter very hot. The heat can deform the metal or weaken it even if it becomes sharp again. To prevent this from happening, it is important to harden the blade often in water during the machining process.
- To cool the blade, keep a bucket full of water near the workstation. When the blade gets hot, dip it in water to temper and cool it. Before resuming sharpening, remember to dry the metal.
Part 3 of 3: Long Term Maintenance
Step 1. Sharpen the blade about twice in each growing season of the lawn
- Regular sharpening is a good habit to adopt. If you use this machine very often, you should sharpen the blade at least twice during the season when you take care of the lawn - or even more frequently, if you mow the grass very often.
- Check the grass after cutting it. If it shows a smooth, clean edge, then the blades are sharp. If it looks torn or frayed, then the blade is most likely dull and needs sharpening.
Step 2. Balance the blade regularly
- If it is not balanced correctly, the blade generates vibrations as it turns which can damage the internal components of the machine. It is worth doing this when it has been disassembled for sharpening, so the advice is to balance it at each maintenance session.
- To balance the blade, you can use a special device called a balancer, which you can buy at garden centers and hardware stores.
- If you don't have the specific tool, you can still do this step. Place the blade on a wooden pin. If one side rises much more than the other, file the opposite one and then repeat the test until the two sides are perfectly flat.
Step 3. Replace broken or dented blades
Although sharpening allows you to restore the good condition of a blade with normal wear, in some cases it is not possible to proceed. If your part is bent, badly worn, dented or broken, then it won't be enough to sharpen it. In these cases, the best and quickest solution is to replace the blade
Step 4. If in doubt, consult a mechanic
- If you have difficulty with any of the sharpening or balancing phases, if you feel like you can't do the job safely or don't have the skills to proceed, then don't risk damaging the blades or injuring yourself. Instead, contact an experienced technician. Virtually any lawn mower repairer can sharpen their blades at a reasonable price.
- For example, you can expect to spend around 10-15 euros for a sharpening at a shop that sells and repairs lawnmowers.
Advice
- Protect your eyes from sparks and debris by using a safety mask if you have decided to use the grinder.
- Once the blade is disassembled and the mower is tilted to one side, take advantage of this to clean the machine of old grass buildup and other debris that has accumulated under the hood, before re-attaching the blade.
- If you have to mow a large lawn or use the lawn mower more than once a week, you will need to repeat the procedures described in this tutorial every 2-3 weeks during the growing season.
- Wear protective gloves when servicing your lawn mower.
- Apply a little release oil on the nut and blade bolt. This will make its removal easier.
- You can only sharpen the blade 3-4 times, after which you will have to replace it.
Warnings
- When using the grinder do not apply too much pressure. If you push the blade against the tool, you cause the metal to overheat, compromising its hardness.
- Do not change the blade immediately after mowing the lawn. The oil will come out of the engine. Make sure you have disconnected the spark plugs and that the mower has cooled down. Do not smoke when working near the machine, as the gasoline fumes inside are highly flammable. Follow the instructions in the lawn mower instruction booklet before attempting any maintenance operation. If the lawnmower works irregularly or abruptly after hitting a stone or other hard object, be aware that the engine may have been damaged, that the crankshaft may have bent or the blade may have suffered breakage or deformation. In any case, you should go to a professional technician or buy a new lawn mower.
