Are Lawn Mower Blades Supposed to be Sharp?

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So you just bought new lawn mower blades and noticed they do not seem very sharp. This raises a lot of questions, like should you sharpen those new blades? How sharp should they be to cut grass? You are in the right place because we are going to answer those questions along with other related topics.

Lawn mower blades should be sharp, but not enough to cut your finger if you touch it. Blades that are too sharp are prone to chipping and dull quickly, making it hard to cut grass. If the blade is as sharp as a butter knife that is good enough.

Can Lawn Mower Blades be Too Sharp?

Yes, lawn mower blades can be too sharp. In spite of what some may believe, very sharp blades actually make it harder to cut grass.

First, new mower blades are already sharpened so no need on your part to do anything. The blades are sharpened to the optimum level and ready to use. Most of these are just slightly sharper than a butter knife and at an angle of 30-45 degrees.

If the blade is too sharp, the edge becomes so thin it breaks off easily in rough terrain or if it runs into rocks and other debris. The blade edge will tend to fold over and slow down your work.

Very sharp blades also dull faster and requires more frequent re-sharpening. The problem is every time you sharpen, bits of the blade are shaved off. Eventually you will have to buy a new one.

So the more often you sharpen, the faster you use up the blades and have to buy replacements, which can get costly. Sharpening often can also lead to mistakes and make the blade come loose.

Image Credit: DuffDude X1

How Sharp Should Mower Blades be?

Obviously sharp blades are necessary to cut grass, but too sharp and it becomes difficult. So the rule of thumb is to hone the blade until it is as sharp as a butter knife, or a bit more so. If your mower is pulling grass rather than cutting, the blades are dull.

Very sharp mower blades are prone to damage on rough terrain. If your lawn has lots of small rocks and debris, razor thin blades will not last. In these cases a moderately edged blade is more efficient.

Another way to put it is this: you should be able to touch the edge without getting cut. If that is the case then you are doing it right. You also have to account for the type of lawn you have and what terrain you will use the mower on. The Craftsman M105 already has the blades sharpened to the right level so no need for any more sharpening.

Flat, even lawns with very few rocks, pebbles or debris are ideal. A moderately sharp blade will cut through the grass easily and will last a long time. In these cases you do not need to do frequent sharpening.

If your lawn is covered with rocks, branches and other debris, your blade will need more sharpening. This is where you have to strike the balance between being sharp and not too sharp.

How to Sharpen Lawn Mower Blades

If you have determined that the blades need sharpening, this process will show how it is done. This is a general guide and should work for most kinds of lawn mowers. Of course you should always check the instructions in your owner’s manual.

You will need:

  • A grinder or hand file (the IKER sharpener is our top pick. It does the job effortlessly)
  • Eye protection
  • Gloves
  • Lubricant
  • Marker or duct tape
  • Bench clamp or vise
  • Screwdriver and wrench
  • Hammer and nail (for balance checking)

Step 1. Wear your eye protection and gloves. Observe safety guidelines.

Step 2. Disconnecting the spark plug is the first thing you should do. This is for safety reasons so the mower does not turn on suddenly while you are sharpening.

Step 3. Tilt the mower onto its side. Tilt away from the carburetor and filter so the fuel does not spill over.

Step 4. Use a marker or duct tape to note which part of the mower blade faces down. This is necessary as you have to put the blade back in the exact position.

Step 5. Remove the screws securing the blade in its position. If you have an old mower the blade might be very tight. Apply some lubricant or cleaner to loosen it up.

Step 6. Once you have taken the blade off, clean it first. Wipe grass and debris off as much as you can. For stuck dirt you can use a cleaning solution. This is an important step because if the blade is too dirty, sharpening will be difficult.

Step 7. Secure the blade in a vise or bench clamp. Now you can sharpen the blade with a hand file or grinder.

Hand file. With the blade clamped down, sharpen at an angle of 30-45 degrees, or whatever the manufacturer recommends. Starting from the interior edge of the blade, push along the outer edge. Put enough force so the abrasion between the blade and sharpener is apparent.

Sharpen the blade until the edge is similar to that of a butter knife. This can take 40-55 strokes depending on how worn out it is.

Grinder. Run the grinder across the blade’s edge at a 30-45 degree angle. Keep doing this until the edge is as sharp as a butter knife.

Grinders are faster than hand files, but overheating can damage the blade. Be mindful of this and if it overheats, stop and let things cool down.

Step 8. After you are done sharpening, inspect the blade balance. Use the hammer to fix a nail onto a wall. Hang the blade on it. If the blade is balanced it should not tilt to either side.

Step 9. When you are satisfied with the balance you can put everything back together. Reattach the blade to the mower, noting which side is down. Reconnect the screws and the spark plug.

Step 10. Turn on the lawn mower and give it a try. If you followed the steps correctly, the blades will cut evenly now.

The entire sharpening process may last 10-15 minutes. If you have an old blade, it is a good idea to have spares available. You never know when the old ones will give out so it is best to have reserves on hand.

You should also have a good socket set so you can easily find one that works with the bolts. Also make sure you wear heavy duty gloves to protect your hands.

How Often Do I Sharpen Mower Blades?

Most lawn mower blades only need to be sharpened once a year. Check the blades before a new season commences for signs of damage or wear. Heavily used mower blades should be inspected after every 10-12 hours.

Your owner’s manual may have its guidelines, but in the end it depends on how much the blades are used. If you rarely use your mower or you have a flat lawn, sharpening once a year will be enough. If you have a large lawn on rough terrain, the blades will need more sharpening.

If your mower constantly goes through rocks, roots, soil and other ground materials, it will wear the blades out more often. So it is important that you check the mower regularly.

If you want your blades to last, try to remove as much of the debris as you can. You cannot remove them all, but getting rid of large rocks will make it easier for the blades to cut the grass.

When Should I Replace Mower Blades?

At some point the blades can no longer be sharpened and you have to replace them. But how will you know when it is time?

The most obvious sign is if you sharpened the blades and the results have not improved. In that case a replacement is a must. But there are other indicators:

  • If the blade has become too thin due to repeated sharpening.
  • Check if the blade is chipped, nicked or damaged in any way. Never use damaged blades because thy are dangerous.
  • Replac if the blade has dents or grooves in it.

If you notice any of these signs, you should get new ones. Before you buy, check the manual or manufacture website for information on what type of blade works best for your mower.