Do you bother to sharpen your lawn mower blade? Why?

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James H. wrote:

It provides the inertia to keep the motor turning. It's almost impossible to hand start the engine without the blade or if the blade is loose and spins on the crankshaft. The small engines that don't use the blade for the flywheel have a heavier flywheel. The aluminum key is actually there only to align the flywheel on the shaft, the crankshaft is tapered and the flywheel is held tight by the nut or starter mechanism. The blade, if it's not bent and there is enough left to sharpen, then sharpen and balance it. Don't worry about getting all the nicks out of it. I usually use the body grinder when I sharpen one, using a file can take a long time, always balance the blade. Ask the local mower shop what they charge to sharpen a blade, and they will have replacement blades and contrary to what the manual says you can usually get replacement at many box stores that will work just fine. Make sure the replacement is EXACTLY the same as the old one. There are 6 point star holes and 4 point and square ones and diamond shaped ones and some have three holes, mulching, non mulching and of course the proper length. I'd stay away from the blades that use inserts to correct for the main bolt hole size. The last blade I bought was made in France and needed balancing even though it was brand new. The last trimmer string feed bump head I bought was made in Italy and is a flimsy POS. Have fun, tell your neighbors, friends, and co-workers you will take their old mowers and weed trimmers, you should have a collection by the end of summer to fix. Surprising how many of them just need a carb cleaning, spark plug, starter rope, cable etc. and they are good for another couple years. Some aren't worth fixing but many have a lot of good hours left in them. Oh yeah, speaking of cables, the one that pulls back the safety brake and kills the engine when you release it, make sure it's in good shape and pulls the safety brake completely back. It will cause a drag on the engine if it doesn't and makes it hard to pull start. It's a good hobby fixing old mowers and weed trimmers, keeps you in shape pulling the starter ropes on those old dogs.
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On Mon, 5 Jul 2010 23:56:23 -0700, "James H."

That's why you check to be sure your blade is tight. I spent many hours on a mower learning *that* lesson. Finally broke down and asked my neighbor to look at it.
First thing he looked at was the blade- 10 seconds and a big wrench later I was good to go.
Jim
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Try starting the mower with no blade. Gently -- the experience is a real arm yanking moment. The blade is essential, in addition to the flywheel.
--
Christopher A. Young
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And the magnito or ignition.
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On Tue, 06 Jul 2010 06:36:54 -0700, Bob Villa wrote:

The flywheel contains a magnet that passes by a coil and induces a voltage in the primary of the coil. Timing is crucial here and why a motor wont start if the shear key has done its job after a blade collision.
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On Tue, 6 Jul 2010 14:01:30 +0000 (UTC), Chief Two Eagles

While you have the flywheel off, clean any surface rust from the magnets and on the ignition. A fine sandpaper will work.
Once had a magnet fall out of the flywheel. Forget what I used to secure it with. (Glue?)
-- cut the grass too the roots and go fishing
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James H. wrote:

Yes that is true, I learned that in shop class back around 1970. Engines with no direct mounted blade normally have a cast iron flywheel, or some kind of flywheel with some weight to it. However, if the motor is worn and doesn't have a lot of compresion, it will run with the blade removed. And it'll scream like a 2 stroke! Did that as a kid with a little 3 wheeled riding mower that was about shot. Wasn't worried if the engine blew.
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Only your grass will know the difference. It will be cut off cleanly rather than torn.
I wedge the blade still on the mower, and then use an ordinary socket and ratchet to remove the bolt. I use a 6" bench grinder to put a new edge on the blade.
You'll find that all mower blades come balanced from the factory. That's why you'll see odd corners cut off on the ends of the blades.
To re-balance a blade: Hammer a 3" nail into a stud so that it's parallel with the ground. Hang the blade on the nail from its bolt hole, making sure it's centered on the nail. Take note of which side is heavier, and grind a corner down a bit on that side. Recheck and refine as necessary.
--
Tegger

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<replying to my own post, here...>

But not always. My current mower's blade was balanced by cutting off the entire end of the blade, so one side is shorter than the other by about 1/16".

Grind a TRAILING corner, by the way.
I use a disc-shaped stone meant for axes in order to lightly dress the freshly-ground edges. You're not sharpening a butcher knife here, so the edge you end up with just needs to be sharp enough to cause some pain when you press your thumb into it, but it doesn't need to be so sharp that it breaks the skin.
I just went and had a look at the nail I use for balancing, and it's a 1-1/4" finishing nail, not a 3".
And finally, UNPLUG electrical cord or spark plug before turning the mower over!
--
Tegger

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Dull blades rip the grass and will burn the top in hot summer, it takes about 15 minutes to use a file yourself.
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James H. wrote:

Yes (3 blades, riding mower), sometimes.

Cuts better. Briefly.
I don't do it as a matter of course, just if I happen to have to drop the mowing deck for something else. And if you think blades are indestructible, you should see mine after a season or two...not much left.
--

dadiOH
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Yes, mostly tradition. A sharp blade cuts the grass easier, a dull blade tends to beat the grass rather than slice it. I do my own sharpening with a bench grinder.
Shears aparently lives on the residual income of off-spec parts. Their mowers won't accept Briggs or Tecumseh parts in many cases, so you end up going to Shears and buy their parts.
--
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James H. wrote:

I sharpen mine every spring. Nothing cuts like a sharp blade. (that's why) Dull blades just tear the grass. If you keep them sharp it doesn't take long on the grinder. If you wait until it's blunt, it may take a while to get the cutting angle planed and edge sharp again. Like any other maintenance, let it slide and it's more work to get back into shape. It also pays to clean up your lawn and remove the rocks. If you never hit stuff it stays fairly sharp. I like a knife edge.
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Interesting. The left side says to keep the blade sharp, the right side says they don't recommend sharpening. Maybe they mean DIY versus a pro doing the sharpening.
Sharp blades do cut better while the dull ones chop and tear the grass apart. I happen to have a belt sander and it does a good job quickly.. A grinding wheel is a bit harder to handle, a file works too. It does not have to be perfect like a butcher knife, but it all helps. Take the same number of passes on both sides to help keep it balanced.
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James H. wrote:

Yes, of course. I'd like to do it every year, but I tend to only get around to it every other year. Same as with the oil (I do top it off a few times every year, though, if it's low).
Jon
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I, personally, do not sharpen my blades. Never have. But if I were to do it, I have about six tools that would do it without me having to remove the blade.
Steve
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I can't imagine paying someone to sharpen a blade. I sharpen our push mower and the double blades on our garden tractor /mower and it doesn't take that long. I do the serious sharpening with my bench grinder, then dress them with a hand file. It probably takes more time to dismount and remount the blades than to sharpen them.
By the way, if you are hitting rocks, stumps or such you might want to clean up the yard a bit. One good "thunk" will bend the crankshaft, and/or take out the lower bearing on most push mowers. Then you don't have to worry about the blade :^)
RonB
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I sharpen my own blade about once a season. A sharp mulching blade on my Snapper cuts much cleaner, accurately and mulches much more effectively than a dull one. It take me about 5 minutes remove blade, 5 to put in vice and sharpen with a file and another 5 to replace. Have done this for at least the last 25 years.
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Roger that!
5 minutes with a file I can even get the nicks out.
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tom wrote:

My walk-behind mower cuts more quietly with a sharp blade because the governor calls for less throttle. It means fewer gas stops and a cooler engine. A sharp blade produces less of the sticky pulp that tends to build up and clog a mower.
If you pay somebody to sharpen it, you also have to take the blade to him.
Once I have a suitable wrench in my hand, removing the blade of a walk-behind mower is very quick. I sharpen with a side grinder. I take care not to overheat the edge, but I'm not sure if overheating will leave the edge softer. I finish up with a big ceramic hone. After installing a blade, I measure the height of a blade tip, rotate 180 degrees, and make sure the other tip is at the same height. Uneven heights would mean vibration.
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