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Kent

Mower blade grind angle?

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Kent
Here's a basic question I don't know the answer to...

I need to resharpen my mower blades, and I've been doing it with a 4" hand grinder. Then I saw new blades pass before my eyes at my dealer, and could see that my angle was no where near a new blade. The new blade looked like it was about 45 degrees, but I didn't actually handle it and check carefully. Mine are not mulching blades, just straight cutters.
1. Is there an ideal grind angle?
2. Is there supposed to be a back cut on the bottom of the blade as well, or is it just a straight grind?

Ciao,
Greg

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Fred
Greg,
I have seen quite some variation in grind angle between brands, but they generally are not as acute as when reground by many people. Something between 45 and 60 degrees seems most common.
One trick I have practiced over the years is to trace the outline of both the whole tip, back into the blade body, and the end profile of a new OEM blade on a blank page of the manual. Or more than one, if they differ. This gives you a great memory aid for regrinding after they get 'chewed'.
And remember never to grind a "step" in the width at the inner end of the sharpened section, but to "swing back" the angle toward the tip when regrinding. A step weakens the blade and can result in a hazard.
The blade bottom should be flat, often not easy to achieve without excessive grinding, but don't leave a weak "wire edge" on the finished grind. I normally 'dust them off' heavily on a wire wheel to eliminate that.
Fred

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Fred
I feel that blade angle is not too critical. If I were mowng sandy ground or where you hit the dirt a lot I would sharpen them at a blunter angle. They will stay sharper longer. If you are cutting clean grass the sharper angle would be better. Fred is right don't grind on the bottom. But sharpen often to not get the up rounding on the bottom edge. Once they are really dull it takes so much metal removal to get to a flat surface on the bottom. This principal applies to chain saws also. Verneer cutters that are cutting low and in the dirt to get every inch of log and bucking skidded logs tend to sharpen 25 degreees, 30 is the most common. 35 degrees works good for clean softwoods, cuts the fastest, and dulls the fastest. My 2 cents worth, but its free. Good luck, AL

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Fred
Thanks Fred and Al. Your comments align pretty well with some other info I got today. I've pretty much heard to just follow the existing angle, but I didn't have one when I started to sharpen these blades. These blades were rounded on both sides. 30 Degrees seems like a good angle, as I do have some sand in my yard. Fred, all your safety advice is very sound. I understand your points, and I'm glad you mentioned them because I hadn't thought about them at all! Well, back to the grinding board...

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Guest
How about if the rocks keep falling out of your head!!?? :<)You'll go broke buying blades!!:>)

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Fred
Well, I did the grind last night, and what a beautiful cut! I think I coasted through my mow last night--no load on the engine at all. But now I wince everytime I hit a root or stick. Alas, the pain..the pain.

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