A guy told me a while back that lawnmower blades shoould be replaced regularly (I think he said something like once a year, if I can remember correctly). Supposedly, this is to avoid the blade breaking at all sorts of inappropriate moments due to stress fracture on the metal. Any truth to that?
Changing blades
- Thread starter Russ
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No. Blades do get banged up quite a bit though if you're not carefull. They need sharpening, ideally every year. And should get balanced and the same time. I hit a partially removed speed-limit sign once on my Sears riding mower (doing good deed cutting the lawn for the neighbor). The blade was really bent and beyond recovery. My push mowers all have the original blades though. I sharpen them at the start of the new season with a standard hand file.
Yeah, the only time you need to replace a blade is if it's bent or otherwised damaged in a way sharpening won't fix. I once hit a rock with a push mower, and it broke the CRANKSHAFT of the engine off, not the blade. Even if it does break, all the damage should be contained under the mower deck.
And in your shorts
I would be more concerned about a cheap cast crankshaft than a maleable steel blade too.
There is no rule as to time only condition of the blade. That depends on how much you mow and in what type of conditions. I only get 10 to 15 hours out of a set of blades in our area. The cut will be affected if you sharpen beyond a certain point. Also if it is a multiple blade mower as you sharpen you will shorten the tip to tip diagonal measurement. If you don't have much overlap it will affect the cut. You might leave strips uncut. We sharpen our blades every day. I can't imagine only sharpening blades once a year. The cut must be quite raggard after a short time. It's also much harder on the engine to cut with dull blades.
I tend to agree with Lawn Ranger about blade maintenance ... but there are so many variables that there is no substitute for periodic visual inspection.
One tip I've heard, and sort-of agree with, is that a razor-sharp blade will chip easier if you strike something hard like a stone. However, for quality of cut and less drag on the mower, I tend to keep mine very sharp.
In general blades (steel) are very tough. I have seen one slice halfway through a railroad spike.
However I find sandy soil really takes a toll on them. Hitting ant-hills, mole tunnels and the like will ruin a blade in just a couple seasons. I have mower blades which are worn so bad they look like curved scimitars. The flaps on the back of the blades had holes in them and were completely eroded away in some cases.
--- Bror Jace
One tip I've heard, and sort-of agree with, is that a razor-sharp blade will chip easier if you strike something hard like a stone. However, for quality of cut and less drag on the mower, I tend to keep mine very sharp.
In general blades (steel) are very tough. I have seen one slice halfway through a railroad spike.
However I find sandy soil really takes a toll on them. Hitting ant-hills, mole tunnels and the like will ruin a blade in just a couple seasons. I have mower blades which are worn so bad they look like curved scimitars. The flaps on the back of the blades had holes in them and were completely eroded away in some cases.
--- Bror Jace
I ran the same blades on my GE Electrack for almost 30 years before hitting one too many rocks with the one. The other is well into its 31'st year.
MolaKule
Staff member
I have never seen a blade break. I don't think blades are that brittle. Most blades are made of a rather soft but springy alloy, tempered to bend a little, and to spring back a little.
In my view blades should be kept razor sharp. This allow you to cut faster and the cut grass looks better.
Here is the problem I see. When repeated grinding and sharpening results in unbalanced blades, or when they are so pitted you can't regrind the edge, then it's time to replace the blades. If they are pitted badly, you can pretty much be guaranteed they will also be out of balance.
I've had two blades break in half right at the spindle bolt. One half of one blade stuck in the side of my barn about 75 feet away. It really made me think. The two blades broke within one hour of each other. Must have been a bad batch of blades. Different companies use different steel to manufacture their blades. Some are hard and brittle and some are soft. The soft ones don't hold and edge in our sand at all.
30 YEARS with the same blades. I'd be thrilled to get 30 hours before a blade is ruined.
As to sharpening, on a single blade mower you can sharpen your blades more times than on a two or three spindle maching. Once you've ground down past a certain point they won't cut well. The lift on the back of the blade normally wears out first around here. I've taken to hardfacing the blades, helps alot.
My house is basically built on old gold mine tailings. The soil is more rock than dirt. We had to bring in topsoil in order to have a lawn. Anyway, in the beginning, we missed some of the rocks so the mower would hit them occasionally. Sometimes it would stop the engine. Really dinged up the blade.
I pulled the blade, put it in my bench vise and chucked a grinding stone into the old quarter inch drill and started working on the cutting surfaces. The blade was pretty badly dented from hitting the rocks. Regardless I was able to grind it back to sharp, and I finished by using a flat file on the two cutting surfaces. Got them pretty **** sharp. Now the mower cuts much better, engine does not slow as much in the thick stuff, and by now we've gotten rid of all the rocks on the surface.
Anyway, I did all this myself in the garage with simple tools, it works fine. These baldes are made of pretty tough steel, they can take a lot of abuse.
OTOH I was at a hardware store and saw a guy bring in a mower blade that was bent in half!! He hit a BIG rock.
I pulled the blade, put it in my bench vise and chucked a grinding stone into the old quarter inch drill and started working on the cutting surfaces. The blade was pretty badly dented from hitting the rocks. Regardless I was able to grind it back to sharp, and I finished by using a flat file on the two cutting surfaces. Got them pretty **** sharp. Now the mower cuts much better, engine does not slow as much in the thick stuff, and by now we've gotten rid of all the rocks on the surface.
Anyway, I did all this myself in the garage with simple tools, it works fine. These baldes are made of pretty tough steel, they can take a lot of abuse.
OTOH I was at a hardware store and saw a guy bring in a mower blade that was bent in half!! He hit a BIG rock.
Bror Jace - One tip I've heard, and sort-of agree with, is that a razor-sharp blade will chip easier if you strike something hard like a stone. However, for quality of cut and less drag on the mower, I tend to keep mine very sharp.
I have seen this many times. One blade maker said they "mill" a 1/64 face on the cutting edge of the blade.
I have seen this many times. One blade maker said they "mill" a 1/64 face on the cutting edge of the blade.
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