How to sharpen lawn mower blades
The blades of the lawn mowers are the sharp metal bars that spin underneath the deck. The blades perform the main task of cutting and trimming the grass. With time and usage, the blades lose their sharpness gradually and they require sharpening after every 20-25 hours of usage . You can use a file, an angle grinder, or a bench grinder for sharpening purposes. Clean and sharpen the blades regularly to ensure the longevity of the mower blades.
You will be able to ensure the maximum sharpness of the mower blades with the proper guidance and the right tools. Sharp blades will trim the grass on your lawn at the desired length at ease preserving the aesthetics of the lawn and make all mowing activities more comfortable.
Removing the blade
The first step towards sharpening the lawn mower blade is detaching the blade from the mower. By following some simple but important procedures to ensure that this process does not damage the blade or the machine.
- If the lawn mower is gas powered, drain all the gasoline to avoid accidental leakage.
- Remove the spark plug. If it is an electrical mower, disconnect the battery. This will stop the mower from accidentally starting during the procedure.
- Tilt the lawn mower with the air filter facing upwards.
- Hold the blade wearing protective gloves because even dull blades can cut your skin and the rust can cause infection. Use 2 inch by 4 inch wood blocks to keep the blade steady.
- Find the suitable wrench or socket to loosen the bolt while holding the blade. Now carefully remove the blade. Store all the bolts, washer and other small parts in a secure place to avoid losing them.
Removing rust
Before starting to sharpen the blade, it is recommended to remove the rust that has been gathering on the blade over time. This can be easily done by soaking the whole blade in vinegar or rust removers. This can also be done using a drill machine or angle grinder with a wire brush disk attachment. If there is minimum rusting, simply use a regular wire brush to dust off the rust. Make sure to wear a protective mask and eye protection as rust is toxic.
Marking the blade
Put a small mark on the side of the blade that you are going to file or grind. This will ensure the avoidance of filing or grinding the wrong side.
Cleaning the blade
Clean the blade with a damp cloth first and then a dry cloth to roughly clean all the dust that has been accumulating on the blade.
Clamping the blade
Whether you file with your hand or use an angle grinder, clamp it nicely and tightly on the workbench. Use a bench vice if possible as it offers the most stability. You can also use C-Clamps or Spring Clamps to attach it to the workbench. Make sure that the workbench does not wobble.
Methods of sharpening lawn mower blade
The three methods of sharpening lawn mower blades are filing with a hand file, grinding with an angle grinder, and grinding on a bench grinder.
Hand filing
This is the cheapest but the most time consuming method of sharpening the blade. File sets for metal works can be bought for $15-$35. Start with a coarser grit file and slowly move up to finer grit. Make sure to start filing on an acute angle close to the blade’s initial angle. Otherwise, the blade can get rounded off. Stroke the file in one direction only. Do not file in the opposite direction. This will cause damage to both the blade and the file. After filing with both the coarser grit and the finer grit, polish the blade using a 400 grit wet sandpaper. Wrapping the sandpaper to the file makes it easier to polish.
Angle grinder
Using an angle grinder is costlier than hand filing but surely less time consuming. The prices vary for angle grinders depending on the quality where the cheapest can be as low as $30 and the higher quality ones can cost up to $250. The next required tool is angle grinder discs.
For sharpening purposes, purchase 120 grit disks. Clamp the blade well to the workbench on a bench vice or with clamps. Grinding with an angle grinder will cause sparks so make sure to wear protective gloves, face shield and long sleeve shirts.
Before starting the grinder, hold the grinder to the level of the blade. The grinder should always be at the exact angle of the blade. Most lawnmower blades are at 30 to 45 degrees.
Otherwise, you will end up rounding off the blade. Make sure to keep the angle steady as you move up and down the blade grinding off the metal. Apply light pressure on the grinder and keep the grinder always moving. Otherwise one point might get too hot and brittle and chip off from the blade making it unusable. Repeatedly check the sharpness to avoid over grinding the blade making it too thin.
Use a finer grit disk like 400 to polish the blade after finishing grinding. Do not grind the blade if it has deep nicks and gouges as it will only deepen the fault.
Bench grinder
This process is similar to the angle grinder but here the grinder is attached to the bench and you will be moving the blade whereas with an angle grinder it is the opposite. A regular bench grinder can be bought for about $200-$300. Choose the proper grinding belt for the bench grinder.
For sharpening purposes, start with 120 grit and move up to finer grits as you continue. Hold the blade maintaining its initial angle to the grinder. Always keep the blade moving on the grinder to ensure that all parts of the blade get the same level of grinding. Like with an angle grinder, do not let any particular point get too hot as it will cause it to become brittle. Finish it by polishing it with finer grit belts like 400 grit.
Safety precautions
All of the methods mentioned above require several safety precautions. The common safety measures are always wearing protective gloves, eye protector, and mask. Wear long sleeve clothes and use a face protector if you are using an angle grinder or a bench grinder. Make sure that the sparks do not fall on any flammable substance.
Never grind at one place for too long and always keep the grinder moving to avoid overheating and chipping. Plug electrical equipment to safe outlets and do not insert multiple machines to one outlet at once to avoid electrical fire.
Post sharpening maintenance
Balancing the blade
It is important to keep in mind that when the blades are getting grinded, parts of the metal are getting chipped off. This decreases weight even if it seems miniscule. Both sides of the blade need to be of the same weight.
Otherwise the blade will tilt to one side or another while rotating which will result in uneven cuts and cause damage to the entire machine. Testing the balance can be done simply by putting the blades center on a small piece of wood or metal where both sides can freely move up and down.
One side will tilt down and the other will tilt up if the blades are unevenly grinded. Whichever side tilts down has more weight and needs to be grinded more. Grind that side again and check the balance. Avoid overgrinding and decrease weight slowly.
Checking the sharpness
Proper method of measuring sharpness of a blade requires tools such as edge tester or knife sharpness tester. This machine measures the force required to cut with the relevant blade.
But more informal methods work as well. Test the sharpness by running the blade on a thin piece of paper or grass to test its sharpness. Keep on grinding up until the blade reaches desired sharpness.
Inspecting for cracks and damage
Before starting to mow the lawn with the newly sharpened blades, it is wise to check for cracks or damage. Cracks and damages can be avoided by grinding properly. Do not use the blade if deep cracks appear afterwards. Lawn mower blades rotate at 2000-3000 RPM. At this speed, even if small cracks come into contact with rocks or other hard objects, it can shatter causing physical damage to the machine and the user.
Reattach the blade to the mower
Reattach the blade to the mower after the blades are sharpened to satisfaction. Do not tighten the bolt too hard as it may cause the blade to bend. Use drops of lubricants to the attachment point before reattaching the blade to ensure smooth rotation. Make sure all the bolts and washers are in the right place.
Testing performance
It is wise to take out the lawn mower on a test run before mowing the whole yard. Fill the gas tank, reconnect the spark plug and get the mower ready. Attach the battery connection if it’s an electric mower. Set the blade’s height to your desire and run it on a small area. Check the consistency, quality, and size of the grass to see if there are any uneven cuts at any place.
Is it worth sharpening lawn mower blades?
Yes, even if someone is at the most beginner level when it comes to handling machinery, it is absolutely worth it to sharpen your own mower blades. The sharpening tools are a one time investment which will come handy in many future endeavors and projects. Even the most time consuming method of hand filing the blades will take 30-40 minutes overall. And using tools such as angle grinder and bench grinder will take even less time.
A well sharpened blade on the mower will ensure not only evenly cut grass but it will cut easily and run smoothly on the ground requiring less physical work. A dull blade will make uneven cuts and jam. This can cause irreparable damage to the machine.
How often should lawn mower blades be sharpened?
Most manufacturers recommend sharpening the lawn mower blades after every 20-25 hours of use. Record how long it takes to mow the lawn on average. Divide 20-25 hours with it and sharpen the blade according to the calculation.
Where to sharpen lawn mower blades?
If you do not wish to do all the work of removing, sharpening and reattaching the lawn mower blade, you can get it sharpened from any workshop in the area. Be sure to check the sharpness before bringing the lawnmower home.
How Much Does It Cost to Sharpen Lawn Mower Blades?
This will vary from place to place as different workshops charge differently. But the bill should not be outrageously high as grinding with an angle or bench grinder does not take much time or effort. It will cost about $20-$60 to sharpen the mower blades.
So do not keep forcibly pushing the lawn mower and get uneven cuts any longer. Take a few minutes of your time and sharpen the lawn mower blade. This will lessen the hardship and beautify your yard with fresh and even cut grass.
