Sharpening mower blade

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llO0DQLE
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Sharpening mower blade

Post by llO0DQLE » May 20th, 2017, 9:57 pm

I am trying to sharpen my mower blade for the first time and I'm not sure I'm doing it all correctly. I used to have my dad sharpen it in the past but I got one of those grinder stones that attach to the drill so I can do it myself quickly.

Image

First thing I noticed was that the angled of the stone didn't match my mower's blade edge. I figured, whatever, I'll just reprofile it. It's taking a lot longer than I expected but, oh well, I'm committed to it now. I've only partially done one side of the blade so far. Here's my question, how far am I supposed to sharpen the blade? I looked up pics on Google and saw that a lot of blades only have about 3 inches of the blade sharpened. Wouldn't this leave the grass in the middle uncut as you go down your path? Also, it seems I have a mulching blade as it has a couple of curves to it. For reference, the middle of the blade is just left to the clamp in the pic above.

Image

Also, if it's not balanced, I have to take some material off the heavier side. I read one guide say not to take it off the edge. So should I just file the backside of it?

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Re: Sharpening mower blade

Post by andy10917 » May 20th, 2017, 10:01 pm

It's really important that you use the original angle, balanced and cut length. If you screwed any of them up, treat the blade as a practice blade.

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llO0DQLE
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Re: Sharpening mower blade

Post by llO0DQLE » May 20th, 2017, 10:48 pm

Is there any detriment to the mower or would that just be an issue of cut quality for the grass? I don't know why the stone grinders are so popular if they don't match the blade angle or is it just my blade that is atypical?

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Re: Sharpening mower blade

Post by g-man » May 20th, 2017, 11:08 pm

[quote=llO0DQLE post_id=307128 time=1495331831 user_id=2927]
Wouldn't this leave the grass in the middle uncut as you go down your path?
[/quote]

The blade doesnt stay fixed. It is rotating along the center of that bolt at around 3000 revolutions per minute (rpm) or ~50 full turns per second. As you move the mower, the blade will cut the front and sides of the path because it is turning in those areas too.

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Re: Sharpening mower blade

Post by llO0DQLE » May 20th, 2017, 11:47 pm

Lol dang what was I thinking.. thanks..


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Re: Sharpening mower blade

Post by g-man » May 21st, 2017, 12:10 am

I had a good laugh when I first read it.

It reminded me of a neighbor asking me for some help to start his new mower to his new house. He tried for 30min pulling the cord. I went there grabbed the safety switch bar, pulled the cord and it started. He never held the safety switch bar for 30min.

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Re: Sharpening mower blade

Post by llO0DQLE » May 21st, 2017, 12:57 am

lol anyway, do you think I should sharpen the blade further into the middle a bit more? I can't tell that well but it seems there's supposed to be an edge on that curved part between the clamp and the part I already sharpened.

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Re: Sharpening mower blade

Post by Swamp_Fox » May 21st, 2017, 4:10 am

The stones can be profiled to match the blades. Personally, I use a file. If I cannot clean the blades up without using a grinder I throw them under my work bench with the other 12.
llO0DQLE wrote:
May 20th, 2017, 10:48 pm
Is there any detriment to the mower or would that just be an issue of cut quality for the grass? I don't know why the stone grinders are so popular if they don't match the blade angle or is it just my blade that is atypical?

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Re: Sharpening mower blade

Post by llO0DQLE » May 21st, 2017, 7:43 pm

Swamp_Fox wrote:
May 21st, 2017, 4:10 am
The stones can be profiled to match the blades.

What do you mean? The instruction says to keep the plastic part flush with the blade. The angle of the stone is not the same angle as my blade, it's thinner. If I had to guess, my blade was 45 degrees, now it's probably 30 degrees.. but I could be totally off, I suck with estimating angles.

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Re: Sharpening mower blade

Post by Swamp_Fox » May 22nd, 2017, 3:55 am

I don't know If you've used bench grinders much llO0DQLE, but they're a good example: you start out with a new wheel that's got perfect 90 degree edges and a flat working area. After use those edges tend to break and round off. A grinding wheel can be "dressed" to like new condition. Just as the center of the disk can get grooves or scale worn in to it too, which dressing also corrects.

If the grinding wheel you bought is too thin and cannot grind at the estimated 45 degree angle you'd want to buy a stone that is set to the same degree as your blade calls for. And really that's your problem, those stones are generic. Stens or whomever manufactures that tool has no idea what angle your particular blade is set at. I do commend you for wanting to do more work yourself! Perhaps a Worksharp sharpener would be a good investment for you? They have plenty of other uses as well, knives, edgers, sheers, hedge trimmers, etc.

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Re: Sharpening mower blade

Post by llO0DQLE » May 22nd, 2017, 7:52 pm

I've never worked with bench grinders so I don't have the tools or the know how to reprofile the stone. In any case, the blade is reprofiled and I guess we'll see how that works. Did my first mow today and seemed to cut fine. I forgot I actually had a file and as soon as I remembered, I used that on the curved part of the blade. I should've just used the file to begin with as it was so much faster and easier lol. I do have DMT diasharp stones for my knives but thought it was overkill for my mower blade...

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Re: Sharpening mower blade

Post by Swamp_Fox » May 23rd, 2017, 12:04 am

Those DMT stones are way to nice for a mower blade my friend! :) The Worksharp is a power belt sander that people seem to really like, they have an attachment for using it with mower blades, though a blade placed in a vice would probably suffice just fine. I'm glad to hear you go your blade wrapped up and that it cut well!

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Re: Sharpening mower blade

Post by llO0DQLE » May 24th, 2017, 1:39 am

Exactly that's why I would never consider using them on a mower blade! Lol Honestly the file worked well with the blade secured between my upper arm and ribs and hand.

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Re: Sharpening mower blade

Post by superkaz661 » June 20th, 2017, 12:03 pm

[quote=andy10917 post_id=307129 time=1495332079 user_id=100]
It's really important that you use the original angle, balanced and cut length. If you screwed any of them up, treat the blade as a practice blade.
[/quote]
I've read Andy's sage posts for several years now, and gratefully accept that he knows better than I do. But on this one, I disagree. There is no magic in the blade angle. In fact, as soon as I purchase a mower blade, I immediately sharpen it with a mill file and put on a secondary bevel such that the primary edge is less acute than the relief (ie. I dont use the original angle). Why? Because when it dulls, I have to remove less metal to get back my primary edge. Is it necessary to have a secondary bevel? No. But it saves me time when I have to resharpen and extends the life of my blade. And my sharpened blades are still paper cutting sharp.

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Re: Sharpening mower blade

Post by llO0DQLE » June 20th, 2017, 2:12 pm

Yeah in terms of cutting ability, the angle, as long as not too extreme either way, is not so much an issue. It will cut the grass. That's why I was wondering why Andy said that and thought maybe it was detrimental to the mower?? Only guess I could make as I've read about how mowers are designed with their own specific blades - something to do with suction etc. and that you can't just swap blades willy nilly. However I don't think blade edge angle is enough of a factor.

On another note, you say you keep yours paper cutting sharp. A lot of people are of the opinion that it shouldn't be too sharp as it dulls quickly. How often do you sharpen your mower blade to keeo it paper sharp? And how big is your lawn and how often do you mow?

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Re: Sharpening mower blade

Post by superkaz661 » June 22nd, 2017, 11:15 am

Cutting edge angle(s) are irrelevant to blade design and suction considerations.

Wrt your question about sharpness, there is a difference between actual sharpness, which it the immediate intersection of material surface angles, and the "broader" edge angle, which many people mistake for sharpness. That is, you can have a very shallow blade angle, but if the first several hundredths round over or are otherwise sloppy, your blade isn't "sharp". In fact, you'd be amazed what you can cut with a crisp 90*.

I can understand if people suggest not to turn the mower blade into a hamaguri. We are cutting grass, not sushi. That said, I get paper cutting sharpness with a relatively steep angle (i.e. over 45*).

Often, especially with crude sharpening instruments like a grinding wheel or angle grinder, people mistake the general angle of the edge for sharpness. You will find that because of the coarseness of grit used, you could put a very shallow angle on the bulk of the cutting edge, but the first few hundredths or so will be fairly blunt. And thats what does the cut. You can have a steep bevel, and if using the right tools, keep that leading edge crisp. I mow about 13.5k feet of TTTF weekly, and sharpen about once a month. Even when my blade dulls, its probably a bit sharper than most. And because of the steepness of my edge, I can and do run over sticks etc without much issue. I have two blades in case something goes wrong, but my current mower is 9 years old, and the first blade is still in service. And you know what? By removing less material, I dont run into balance issues either.

Again, is my way the "right" way to do it. No. Again, we are cutting grass not sushi. But I do what I do because it works for me.

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Re: Sharpening mower blade

Post by llO0DQLE » June 22nd, 2017, 2:36 pm

Yes I totally agree with you. It is hard to get that crisp edge though esp for people who are not really into sharpening blades. What do you use to sharpen? I just use a bastaRd file. I get the blade into "good enough" category because I'm not that skilled with sharpening.

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Re: Sharpening mower blade

Post by superkaz661 » June 29th, 2017, 10:39 am

[quote=llO0DQLE post_id=310228 time=1498156584 user_id=2927]
Yes I totally agree with you. It is hard to get that crisp edge though esp for people who are not really into sharpening blades. What do you use to sharpen? I just use a bastaRd file. I get the blade into "good enough" category because I'm not that skilled with sharpening.
[/quote]

If its needs more material removed, Ill use a Nicholson 12" bastard. But usually its a Grobet 8" second.

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Re: Sharpening mower blade

Post by canairb » June 29th, 2017, 1:24 pm

I use an angle grinder with a flap disc.

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Re: Sharpening mower blade

Post by Cyrus » July 13th, 2017, 9:17 am

I use this and it is awesome. Has the required 30 degree sharpening angle welded onto the sides.
http://www.rbggrinders.com/712.html

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