Do you sharpen new lawnmower blades?
When you buy a new lawnmower 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 lawn mower blades come sharpened? The simple answer is Yes. 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 hard edge that do the work.
How much cut time could I expect to get out of a new blade?
The average time in between sharpening lawnmower blades in most manuals is around 25 hours. This may sound like you will need to sharpen them 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 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 blade or 26-35 cuts.
Before you get too excited there are some variables.
If you are mowing lawns in extreme conditions.
A sandy lawn will wear your blade out faster. This can be even worse if you are using a mower with an aluminum body as you will wear out your axels in no time and that’s one of the main reasons that mowers cut unevenly.
A lawn with a lot of stones or next to a pebble garden will also damage your blades. Every little nick in the blade reduces the effectiveness and the quality of the cut. You will need to maintain your blade 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 just as much 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 lawnmower 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.
How to check your blades.
Always 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.
It goes without saying that you should turn it off and remove the spark plug first also watch out for the muffler if the machine is hot.
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.
The first thing you should check if your 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 but hitting an object.
A bent blade will need to be replaced. Blades are made out of pressed steel so the cannot be bent back.
I normally keep a new 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 and an old one will do.
If you do not have another blade to compare it too, 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. 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 therefor avoiding bending the crankshaft.
It is possible to break the keys, 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 you 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 get to 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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