Lawnmower Blade Sharpening

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tdgeek

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#243272 4-Dec-2018 09:15

I have a new mower, a not cheap one, so I thought I'd ring Stihl to get the lowdown on how to sharpen the blades properly. Rather then what I used to do, attack them with my hand grinder. I was hoping them to say, we have the file here that is ideal, or we have a stone, but they said use a grinder. From my experience a hand grinder isn't very accurate depending on how steady you are.

Is a file a good option and what type?

A stone be too slow?

Or a bench grinder so I can remove unsteadyness and get a straight edge. Would they have a means to hold the blade at the angle I want or is it me having to hold and steady the blade?

Mower is Masport President AL6000 21" quadcut blade

TIA

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#2139005 4-Dec-2018 09:19

I use a flap disc on my angle grinder to sharpen my lawn mower blade, cold chisels and garden tools. It does a pretty good job I reckon.

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#2139009 4-Dec-2018 09:35

DarthKermit:

I use a flap disc on my angle grinder to sharpen my lawn mower blade, cold chisels and garden tools. It does a pretty good job I reckon.

Great idea. Being less harsh means less or no gouging. What grit would you recommend for a mower blade?

mdf

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#2139010 4-Dec-2018 09:37

A flap disc is less aggressive than a grinding wheel, but they are still pretty ruthless. Practice and care would still be required.

I've just converted to using diamond stones to sharpen my hand tools (admittedly much smaller than a lawn mower blade) and even using a dirt cheap one I got off e-bay it is *so* much faster than using a traditional stone. If you were considering going the hand sharpening route, that would be my pick.

Almost all bigger bench grinders I've seen have a rest to help you keep things at the right angle (some smaller ones don't). You'd still have to practice or build/find a jig, as you'd move the blade along the grinder rather than vice versa. The aluminium based abrasive wheels for steel do heat up, so you'd want to have plenty of coolant on hand not to spoil the temper. ~~If you really wanted to go fancy, you could upgrade to a CBN wheel.~~ Stumpy Nubs has the low down on those.

EDIT: Just rewatched the CBN video. Apparently not a good idea to use CBN wheels on mild steel like lawnmower blades.

Gordy7

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#2139011 4-Dec-2018 09:39

I use a bastard file and touch up the blades in place... about 5 to 10 strokes... blades don't need to be razor sharp... Try to remove about the same amount from each blade to preserve balance.... I used to use an angle grinder but control was difficult when sharpening in place and removed too much blade material...

Remember to disconnect the spark plug before starting...

Gordy

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1101

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#2139646 5-Dec-2018 09:55

Mower blade : not a precision instrument .

Just use whatever you tool of choice is. After a few weekends it wont matter how you sharpened it :-)

Gordy7

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#2139649 5-Dec-2018 10:00

1101:

Mower blade : not a precision instrument .

Just use whatever you tool of choice is. After a few weekends it wont matter how you sharpened it :-)

Gordy

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#2139653 5-Dec-2018 10:08

Growing up on a farm i used to sharpen tractor mower blades and push mower blades with an angle grinder, put the blade in a vice so it doesn't bite and take your face off and you should be good.
You only need to lightly glaze over the surface on a consistent angle. Any edge is better than a rounded one.. The second the mower hits dirt it dulls the edge anyway..

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tdgeek

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#2139662 5-Dec-2018 10:25

I'd like to touch it up every now and then as I mulch mow 99% of the time. I think I will try the file option first, that gives maximum accuracy and the best sharpen:loss of metal ratio. Next will be the flap disk on and angle grinder, which for me is a new grinder as my cheap one has a 3 prong tool to remove the disk, but I dont have the tool anymore, don't even recall seeing it. Another cheapie would do

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#2139679 5-Dec-2018 10:54

I file my blades after about 3 mows (6 weeks, 3x 500 sq m lawn).... depends on how long the grass is too... the OP has not said if he will catch or mulch the grass... I would definitely keep the blades sharp for mulching... missed the previous post... Op is mulching..

Gordy

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DarthKermit

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#2140181 5-Dec-2018 22:09

tdgeek:

DarthKermit:

I use a flap disc on my angle grinder to sharpen my lawn mower blade, cold chisels and garden tools. It does a pretty good job I reckon.

Great idea. Being less harsh means less or no gouging. What grit would you recommend for a mower blade?

The one I have (I found it on the side of the road actually) has 40 printed on it. Seems ok for what I use it for.

andrewNZ

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#2140186 5-Dec-2018 22:26

Be aware, new flap disks are SUPER aggressive. They dull in a pretty short time and are great, but the first few minutes using a new one... They make a normal grinding disk seem delicate.

tdgeek

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#2140296 6-Dec-2018 06:47

Gordy7:

I file my blades after about 3 mows (6 weeks, 3x 500 sq m lawn).... depends on how long the grass is too... the OP has not said if he will catch or mulch the grass... I would definitely keep the blades sharp for mulching... missed the previous post... Op is mulching..

Why I got onto this, is that the last mow, the mulching wasnt as normal. Grass was a tad long, but the mower was also bogging at times. I clean it using the wash port, but haven't the last couple of mows. It was heavily caked in grass, so cleaned that all up. It seems the small clippings can do this more than longer clippings? The underside was cleanish, but once I had a better look there were many very thick clumps. Next mow I will see if that is a 100% fix. But in any case I want to keep them in good nick, without grinding the blades away, hence I will whip the blade assembly out and give it a quick file after the next mow

Thanks for the info, appreciated.

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#2140836 6-Dec-2018 21:39

I have a couple of "attach to the drill" type sharpeners for my mower blades (I mulch and need to be much less lazy in terms of maintaining the blade). So far I've been too chicken to sharpen the blades, so I've purchased a new blade, with good intentions to actually give the old one a sharpen (safe in the knowledge that if I stuff it up, I still have a sharp blade).

I'll endeavour to look at this over the weekend and report back early next week!

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#2140883 7-Dec-2018 05:21

I agree with the ones saying this is not a precision exercise.

Mower blades are made from mild steel to prevent them exploding when they hit something. They will be dull within a short time of using them but tend to keep a round edge from the wear. It’s the speed and power of the turning blade that does the cutting. I sharpen my tractor mower blades every once and a while but the hand mower I never bother.

tdgeek

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#2140890 7-Dec-2018 07:17

wazzageek:

I have a couple of "attach to the drill" type sharpeners for my mower blades (I mulch and need to be much less lazy in terms of maintaining the blade). So far I've been too chicken to sharpen the blades, so I've purchased a new blade, with good intentions to actually give the old one a sharpen (safe in the knowledge that if I stuff it up, I still have a sharp blade).

I'll endeavour to look at this over the weekend and report back early next week!

I agree that a blade doesnt need to be that sharp, a butter knife edge is often quoted. Mulching though, the sharper the better, although I wouldn;t go to the extreme of excessive sharpening or too often. I might get another blade, the 4 flails are not expensive although it would be convenient to buy the whole assembly just for time saving.

If I use a file which I think is my plan now, I wont mess it up, as its slower to remove metal, start off slow, etc.

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