Should You Sharpen or Replace Your Lawn Mower Blade?

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Many lawn owners know that they should maintain quality blades on their mower but unfortunately, it’s one of the things that many people skip completely. Sometimes it’s a pain to get under the mower, take the blades off and either get them sharpened or replaced. While it can be a hassle to do this, proper maintenance of your mower’s blades is absolutely necessary to get great results for your lawn.

You may be wondering whether you need to sharpen an existing blade or replace it entirely so that’s what I’ll try to answer here…

The short is answer is…

If the blade is dull, you only need to sharpen it. If the blade has become damaged so that it’s no longer in balance, or the outer edge of the blade has become so thin that you can see cracks in the blade, you should replace it.

The Importance of a Quality Mower Blade

The majority of mower’s blades spin at around 3000rpm so that the tip of the blade is spinning close to 200mph. It shouldn’t be a surprise that regular use of your mower is going to cause normal wear and tear. 

Hitting rocks, twigs and other debris can cause blade damage which can cause the blade to warp which can impact air flow. 

It’s also important to note that a mower’s blade can become bent which will need to be addressed.

Faulty blades can make a big difference!

Not only can they affect the cut of your lawn, it can also cause wear and tear on your pulley system and gear spindles.

One symptom of a dull mower blade is ripped grass blades.

The ends of the grass can become frayed which can cause excess moisture loss, increase risk of disease and a brownish color which can ruin the appearance of your lawn.

The problem is that it can be tricky to know whether a particular problem is caused by dull blades or some other reason. For example, one other reason why your grass may be frayed is that your lawn mower is under powered. As mentioned previously, the blades spin at around 3000rpm. If this is too low, the blades of grass will tear instead of a nice clean cut. To avoid this, I recommend you purchase a lawn mower with a good amount of power even though it may cost a little more.

No matter how good the other aspects of your lawn care maintenance program are, your lawn will not get that appealing look you desire if you do not cut with sharp, undamaged blades.

Knowing When to Replace the Blade

It’s not just about keeping the blades sharp. You also need to make sure they are in balance and free or damage. The vibration of the blade and the airflow is very important. If it gets out of balance, it can totally ruin the cut quality. I’d recommend picking up a blade balancer for sure (link to Amazon). 

The top fin on the blade acts like a fan to pull the blades of grass up and this begins to start thinning out and gets chipped over time. Sometimes pieces of metal can start flying out from under your mower which obviously poses a safety hazard. In this case, you’re going to need to fully replace the blades.

Avoid trying to weld them. This will just make the blades become brittle.

It’s critical that you replace a damaged blade!
Even if the blades are sharp, you will still have problems with the blades cutting the grass.

Bent Mower Blades

If you accidently hit a large rock, tree stump or any other large debris, your mowers blade may become bent. This will result in an uneven cut where your grass height is uneven – almost like a bad haircut.

If your mower blades are bent, you will always need to replace them with new blades.

Don’t try and bend them back into position. Trying to straighten them out will usually not be effective and could cause the blade to become weak which could potentially be dangerous.

It’s a good idea to keep two mower blades on hand at all times!
By doing this, you can change the blades immediately. It also gives you plenty of time to get the spare sharpened up for use.

Removing the Blade

First, you need to disconnect the plug wire. This is really important because turning the mower blade manually could actually start the mower.

Before placing the mower on its side, place sandwich bag under the gas cap and the screw it over so that gas does not pour out when you tip it over.

Use a pair of vice grips to clamp down on the deck next to the blade so that it can’t move past it.

Next use a wrench to unscrew the nut by turning anticlockwise. You may want to use some WD-40 if the blade is heavily rusted and or bent.

Wondering if mower blades are universal?
Click here to find out!

Replacing the blade

It’s useful to take your old mower blade to wherever you will be purchasing a new blade from. By doing so, you can make sure to get a blade of the correct length with the right hole configuration.

It’s important to put the blade back on the correct way around. There should be an indication of which side should be facing where on the mower blade itself.

When you screw the nut back on, be sure to switch the vice grip to other side of the blade (opposite side to removing the blade). Make sure you screw the nut back on very tight.

Knowing When to Sharpen the Blade

You should sharpen the blade when it becomes dull but not damaged!

Here are some of the signs that your blades are dull and you need to have them sharpened:

  • Your grass height is uneven after mowing
  • Your grass blades are ripped
  • Brown grass

A sharp blade is absolutely necessary for a good looking lawn. Mowing with dull blades can leave your lawn looking… dull but is it even worth sharpening a blade? Why not just put on some new ones?

Here’s my take on it…

If you have a single mower blade it’s relatively quick to pull the mower blade off, sharpen it and put it back on. If you having a riding mower, you’ll be dealing with three blades instead of one which can be more time consuming. On some mower’s, you can actually sharpen the blade without removing it which can save you quite a bit of time.

In a lot of cases, it may be easier to put on a brand-new set once a year. You can get a three pack of new blades for under $50 so it’s just a case of time vs money. I like to replace my mower’s blades once a year and then keep the old ones as a backup set.

How Long Should Mower Blades Last?

It’s difficult to give an exact time frame on how often you should sharpen or replace your blades. The general recommendation seems to be to sharpen the blade every 25 hours of mowing time.

From my experience, it’s idea good to swap out your mower’s blades every few seasons or so, but you should sharpen your blades at least once a year.

How often you switch them out will depend on a number of factors such as…

  • How large your lawn is
  • Blade quality
  • How often your mow your lawn
  • How well you avoid causing damage to the blade

In any event, it’s good to regularly check the blades are not dull, damaged and remain in proper balance so that you can get the best possible cut.

What Will Cause the Blades to Wear Out Faster Than Normal?

The best way to make your mower’s blades last longer is to avoid running your mower over any debris that could damage the blades. Of course, it’s inevitable that you will ocassionaly hit rocks, twigs and other debris over time but you should try to avoid this as much as possible.

Do Brand New Blades Need to Be Sharpened?

If your lawn mower is brand new, the blades will not need to be sharpened. The blades from the manufacturer will have already been sharpened so it will be not be necessary.

Sharpening the blade

As far as sharpening the blade, the only part that really matters is the very outer edge since this is the part that actually cuts the grass.

Using a vice and a regular file, it’s quite easy to sharpen the blade.

You can also use a sharpening tool to get the job done too (I like this all-in-1 knife).

It doesn’t really matter how you sharpen the blade; the end result is what counts.

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