The importance of having sharp lawnmower blades
Many people will mow their lawns regularly, but I’m willing to bet that less than half of them actually take the time to sharpen their blades. A lot of people might not realize how important it is to keep your lawnmower blades sharp, so in this article, I’ll aim to share with you why you should really think about doing it.
It’s a fact that most homeowners don’t bother sharpening their blades until they start noticing problems with the quality of the cut. Duller blades tend to tear the grass instead of cutting it cleanly as they should, which means you’ll end up with a lawn full of raggedy-looking patches.
A sharp blade will cut through grass quickly and easily without tearing the grass blades. A lot of people might think that if their lawn has areas where it is starting to look patchy, then it just needs more fertilizer or better watering – but that’s not always the case!
It’s worth mentioning that a dull blade can also create a buildup of pressure beneath it as it cuts through the grass, which could lead to problems with the lawnmower’s engine. So if you suspect that the mower blade might actually be dull, then it’s worth checking your owner’s manual to see what the manufacturer suggests for getting rid of buildup like this – often, it will tell you how often you need to replace the blade.
Sometimes, even with a high-quality lawnmower, blades can become bent or warped over time – this is especially true of lawnmowers that are stored outside during winter months (if you do store your mower outside, then make sure to take good care of it by covering the deck and wheels with some plastic sheeting). The easiest way of spotting any problems with blades is by inspecting them after each use. A slightly warped blade won’t cause too many issues, but a badly warped blade could be causing your lawnmower to vibrate while it’s being used, which will cause the engine to work harder at cutting the grass.
It’s also worth mentioning that if you’ve recently had new blades fitted, they might not have been sharpened correctly during installation – so once again, it would be a good idea for you to inspect their condition after each use. If there are any problems with them, it’s best not to continue using them because they could damage your mower deck in the long run!
How long does a lawnmower blade stay sharp?
The answer to this question is, it depends. If you’re referring to the length of time before the grass starts looking like it’s been chewed on by a herd of elephants, then your guess is probably right around forever. On the other hand, the average person puts in about 8-12 hours per year maintaining their mower blade – and never comes close to sharpening it! Well, there are some steps that can be taken to extend the life of your blade – about twice as long should do the trick.
Step 1. Mow often enough
This should go without saying, but I’ll say it anyway: You should mow your lawn every week or two (more often if needed) during peak growing season — for most folks, that’s spring/summer. The thing is if you don’t mow often enough, not only will the grass get too high to be cut properly (but even worse than that) . . . it’ll actually encroach on the rotor blades and dull them – pretty much negating the entire purpose of having them!
Step 2. Keep your lawn short during the cool season
Also obvious but sometimes forgotten: If you’re like most people, you probably let your lawn go dormant in winter (meaning no real “growth” happens). Many fail to consider that when there’s no growth, there’s also no need for chlorophyll, which means less moisture can be held by the blade, resulting in a very dull edge over time. So, mow every two weeks to a month during winter, and you’ll be amazed how long that blade will last.
Step 3. Sharpen your blade once a year
Regularly maintained blades actually stay sharper longer than infrequently sharpened ones. If you sharpen your blade only on the eve of the first snowfall, it’s going to dull pretty quickly as soon as there’s some lawn growth again. If you keep a small file on hand (it doesn’t have to be anything special), all you need is a couple of minutes each time – no matter where or when it needs to be done. And remember: discard those cheap pull-through “sharpening” devices . . . they’re doing more harm than good!
4. Sharpen your blade with the right tools
There are basically three ways to sharpen a lawnmower blade: An automotive file, an angle grinder, or an electric drill attachment. Of course, all methods have their pros and cons, but it’s generally accepted that using an angle grinder is the fastest method (but also generates the highest amount of heat). The same holds true for the drill-mounted sharpener – just be sure to wear safety goggles! Also, note that using/buying professional “recycled” blades can often cost less than trying to keep your own in tiptop shape.
Step 5. Keep blades clear of built-up grass clippings, etc
There are plenty of moving parts on your lawnmower – and a simple layer of grass clippings, mulch, or pine straw can cause a lot of unnecessary wear and tear. So, after you’re finished mowing, always remove the blade(s) from the machine and use a wire brush to clean all built-up debris from between the blades.
Step 6. Keep them balanced
While not as common as sharpening issues, out-of-balance blades are also responsible for prematurely dulling your lawnmower’s cutters – often due to vibration damage! If you notice that one side of your blade seems much heavier than the other (and especially if it only seems off by a few grams), first try cleaning all grass clippings from both sides.
Sharpening rear bag blades.
I get a lot of questions about sharpening the blades on the rear bag. Unfortunately, most shooters are not aware of the ones they have been rounded over. This makes it difficult to get the level of support needed. The trick is to round over your blade like this:
I was given this technique by Ray Chapman many years ago. Ray used to run his file down the sides on both sides of the blade until he had cut about 1/2 way through. This gave him a sharp edge that would not roll under recoil and allowed him to get maximum support from the rear bag. I use a 3/4″ wood rasp from Home Depot. It worked great and was cheap.
Place the blade flat on the bench with the shooter’s side facing up. Hold it down firmly with your left hand (if you are right-handed). With the file, make downward strokes like you would sharpen an ax. Although your first strokes will probably dig deep holes in the steel, do not be discouraged; you had to remove some metal somewhere to sharpen this tool; that is what these “holes” are. Keep filing until you start seeing shiny metal along the edge of the blade, then flip it over and repeat on the other side.
Can you sharpen lawn mower blades without taking them off?
There’s a myth that you can’t sharpen lawn mower blades without taking them off. The excuse is usually “I don’t have a vice large enough to hold the blade.” Well, I’ve been sharpening mower blades for over 40 years, and ALL of mine were sharpened WITHOUT removing them from the mower. Sure, there’s some extra work involved, but it will be well worth it when you finish. First, you need to make sure your blades are balanced or unbalanced (click here to learn how).
Take off any weights on the blade since they won’t do any good once they’re removed. Next, check all of your offset holes (drilled into each end of the blade) to make sure they’re not plugged up. If they are, try to scrape them out. Next, you’ll need a grinder since that’s going to be the tool of choice for this job. If you don’t have a good grinding wheel on your bench grinder, it will make the job much harder for you. Next, sharpen both ends of each blade at the same time since sharpening one end will make the other end dull from dragging against it while spinning. You can usually feel when an end is dragging, so stop and fix it before doing any real damage to your blades. There are two different types of mowers; A side discharge (push) mower like these:
or A rear bag (walk behind) mower like these:
You need to sharpen both sets of blades, but you’ll do it differently for each type of mower since I’ve already covered sharpening rear bag blades (click here to learn how), let’s get started on the push mowers. First, sharpen all four sides equally, or your mower will vibrate like crazy while cutting. You can mark the sharpening angles on the blade with masking tape if you need to. Be sure to move your marks around evenly around the entire blade, so you know they’re correct (you don’t want 1/2 your blade one angle and the rest another). If your blade is badly nicked or rounded over from hitting a rock, then use a file instead of a grinder.
After grinding both ends, fit them back on the mower and make sure they fit tight against the mower deck. If either end of a blade is too small to lay flat on the deck surface, remove it and grind it some more. Don’t get in a rush when putting your blades back on because a sloppy fit will cause uneven cutting or vibration while running, which can damage your motor. However, with good balance and sharpening, you should be able to get 10 – 14 cuts per inch from new mower blades.
How sharp do mower blades need to be?
Mowing your lawn with dull blades is a good way to damage the grass and cause premature wear on the mower. By maintaining sharp blades, you can decrease mowing time by up to 25% (due to smoother operation, soil aeration, and reduced compaction). You will also reduce emissions, noise pollution, and fuel consumption.
Maintaining sharp blades is not the only way to extend the life of your mower. The two other most common causes for premature wear of the mower are poor lawn conditions and incorrect maintenance practices. This article will focus on blade maintenance, while I am working on another article that will address proper mower maintenance.
Before we get into how sharp do you need to go, let’s define what exactly “sharp” means in this context…
A metal cutting tool may be described as either dull or sharp relative to some baseline. A dull tool has a surface roughness that causes it to slide over rather than cut the material with which it comes in contact, thus causing more force per unit area (applied). By contrast, a sharp tool has an edge with micro-sized points and valleys that bite into a surface of a material, thus requiring less force per unit area (applied).
An abrasive sharpening stone is a good example of this concept. The more coarse the stone, the more material you must remove from your blade in order to get it sharp again. And removing more material equals dulling of the blade more quickly. In contrast, finer grits will hone blades but not cause as much dulling over time.
*How do you get your blades sharp? There are many ways to sharpen mower blades, but I don’t recommend trying them yourself unless you own a grinder or jig/fixture designed specifically for sharpening lawnmower blades.
What about lawnmower blade sharpening jigs?
Jigs are designed to allow you to sharpen lawnmower blades quickly and efficiently. By using a fixture, jig, or simple guide, you can touch up your blades without removing them from the mower deck. These items function by placing your blade at an angle against a rotating abrasive wheel that allows you to take off enough material (very little) to get the edge back. This is crucial because too much metal removal will dull your blade faster than desired – defeating the purpose of sharpening it in the first place! Be sure to check out our other article on how do I know when my blades need to be sharpened.
What about lawnmower blade pullers?
If you do not have access to a grinding wheel, jig, or fixture, then there are other ways to sharpen your blades. For example, you can carefully grind the edge of the blade on an abrasive surface (stone, concrete, etc.) until you get it back to an acceptable cutting angle.
You also may be able to remove the blade and use vice grips on the flange while rotating the blade against sandpaper wrapped around a large bolt. Yet another option is using steel welders gloves to hold your blade in place while drawing it towards yourself along an old piece of sandpaper lying upon a flat surface. Just make sure never to run your finger across this sharpened area — these methods are for the metalworking, after all.