Do New Lawn Mower Blades Need Sharpening?
When you buy a new mower or a set of new blades you may have noticed that the blades look blunt and are usually powder-coated. You may be wondering if your blades need sharpening before you use them.
Do New Lawn Mower Blades Need Sharpening? The simple answer is no, they do not need to be sharpened. You can go ahead and mow your lawn. A lawnmower blade is not meant to be razor-sharp. It is the speed of the blade rotation and the flat edge that do the cutting.
How much cut time could I expect to get out of a new blade?
The average time before blades need to be sharpened in most manuals is around 25 hours of use. This may sound like you will need to sharpen the blade quite often but this is not the case. 25 hours is a long time in engine hours as it doesn’t include the time you spend getting organized and cleaning up or edging before a mow.
I ran timers on half a dozen commercial mowers doing domestic lawns and kept a monthly log for over two years. I found that your average mower did somewhere between 12-15 hours a week and I was getting around 50 hours out of the blades before they got a dull blade and needed sharpening. If you translate that to a private domestic lawn that you are mowing then you should be able to get at least a year out of a new mower blade or 26-35 cuts.
A few things that will shorten your blade life.
Mowing lawns in extreme conditions.
A sandy lawn will dull lawn mower blades faster. This can be even worse if you are using a mower with an aluminum body as you will wear out your axel fittings in no time and that will cause your mower to cut unevenly. This will produce uneven wear on your blade.
A lawn with a lot of stones or next to a pebble garden will also damage your blades. Every little nick on the edge of the blade reduces the effectiveness and affects the quality of the cut. You will need to sharpen your mower blades more often.
Mowing your lawn too low.
You shouldn’t be doing this anyway. Most lawns do not like to be cut too short. Not only does it damage the lawn and encourage flat weeds it does damage to your blade.
Your blade will last a lot longer if you cut your lawn high. It will also encourage that nice green healthy look so that is a win-win all around.
How do you know if your blade is blunt?
The easiest way to tell is to look at the grass that the lawn mower is cutting. if you pick a piece of grass and look at the cut, it should be clean. No bruising on the grass and a straight cut as opposed to a tear.
Can a blunt blade damage my lawn?
Yes, there are a few things that can go wrong with your lawn if you cut it with blunt blades.
- Brown or yellow patches in the lawn – Where the tips of the damaged grass die off.
- It can look ragged and unappealing.
- It is more suspectable to disease.
- It encourages fungus in wet weather.
Here is an article from the University of Maryland that goes into more detail if you would like to read more.
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How to check your blades.
Always disconnect the spark plug and lift your mower up from the front. Do not tip it on its side to check your blades unless you are running a two-stroke. If you try this with a four-stroke (a mower with a dipstick) you will either flood the air filter with oil or pour oil straight into your muffler. Both are bad, so avoid stress and always lift from the front.
Also, watch out for the muffler if the machine is hot.
You can get the Ryobi Impact driver here and if you don’t want to use a grinder you can get a blade sharpener here.
How I Sharpen My Blades in My Lawn Care Business.
Clean the mower – Not 100% necessary but it makes the job nicer.
Remove the blade – Remove the spark plug cap. Use either a socket wrench or a Ryobi impact drive (as seen in the photo). I prefer Impact drives as I can adjust the tension when bolting the blades back on. I use the middle setting.
Compare the blade with a new blade – Make sure it is not bent.
Put the blade in a vice – When I sharpen lawn mower blades I give the blade around twenty strokes with the grinder on each side (at a 45% angle). You could use a blade balancer to check that the blade is properly balanced. I do have one however I don’t use it. If you count the strokes and keep them even then you should be fine. The blade does not have to be razor sharp, If you can see new steel in the entire cutting area, the is sharp enough.
How to tell if the blade needs replacing?
If your lawnmower is not cutting correctly it may be time to replace the blades. One of the telltale signs is that the mower is no longer cutting evenly.
Now there are a few reasons why this could be happening.
- The blade is bent.
- The crankshaft is bent.
- Your bushes are worn on your axles.
- The blade is worn out.
If you are getting an uneven mow.
Look at the axles on the mower where they pass through the body. Is there any play?
There may be some plastic bushes there and they can wear out. Replacing them is not expensive and may solve your problem.
Spotting a Bent Blade.
This is usually caused because your mower has hit something. You can dio this without even noticing sometimes.
If this is the case then you will need replacement blades. Blades are made of pressed steel so they cannot be bent back.
I normally keep a new lawnmower blade on hand so I can lay it on top of the suspect blade and this will tell you immediately if the blade is bent. If you haven’t got a new blade then an old but unbent blade will do.
If you do not have another blade to compare it to, then a blade balancing tool will also tell you. These are cheap to pick up and they are also handy when you are hand sharpening a blade so you don’t take too much off one side.
Another easy method is to lift your mower up, remove the spark plug cap, and turn the blade. Mark the level where the edge meets the body and then spin the blade and see if the other side matches the same mark. If not the blade or the crankshaft is bent.
Checking the crankshaft.
This normally happens when you hit something hard. There are a couple of small metal teeth (keys) that are on the blade holder and if the blade hits an object they will break off therefore avoiding bending the crankshaft.
It is possible to break the keys, and bend the blade and the crankshaft in one unfortunate event. If you suspect that your crankshaft is bent there is one easy method for checking. Remove the blade and spin the blade hub.
Is it spinning evenly? If you are not sure then attach a pair of vice-grips to the blade hub and spin it again. It should make any uneven turn more obvious.
If your crank is bent then that’s a trip to the mower shop. With a bit of luck, they will be able to straighten it if the damage isn’t too bad. You will probably want to pick up a blade while you are there.
How to tell if your blade is worn out.
Funnily enough, I have never had an undamaged blade that stopped cutting after a good sharpening. However, there is a point after about ten sharpens that I throw them away. I use a grinder to sharpen my blades and once they reach the point where I have removed a third of an inch of each side I retire them. I figure they’ve worked hard enough
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In Closing
In conclusion, while brand-new lawn mower blades may not need sharpening right away, taking the time to properly sharpen blades is an important part of lawn mower maintenance. Rather than always buying new blades, learning to sharpen your existing blades is a better way to prolong their life. It’s easy to sharpen blades yourself by laying the mower on its side and using a file or grinder to hone the cutting edge on both sides of each blade. Being sure to balance the blade after sharpening helps ensure a quality cut.
Sharpening blades allow grass to be cut with a sharp blade rather than a dull one that can damage lawns over time. Checking blades periodically and sharpening as needed before they become too dull is the best way to maintain a good quality cut. With regular blade sharpening, homeowners can avoid having to buy new lawn mower blades unnecessarily and get the most use out of their equipment. A sharp, balanced blade is essential for the smooth operation of any lawn mower.
Once you have got your blades sorted the next question is “How often should you be mowing your lawns” This will vary depending on where you live. However, the post called “Does cutting grass make it grow faster? may help you get your timing right.
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