What's the correct way to sharpen a mower blade?

[sixdogs]

New blades don't come with a sharpened but a somewhat dulled edge. Now that I'm sharpening mine, does a sharp edge cut grass better than the slightly rolled edge? It's a 7' pull type mower and I using a hand held grinder and not removing very much material.

 

[4570Man]

I think the slightly dull approach is better. It doesn’t take long for the razor sharp blades to dull worse than you started with. And I’m not in the sharpen blades forever crowd. After a couple sharpening the square edge is gone and cut quality suffers.

 

[tomplum]

Painted blades can appear dull. Typically I will sharpen rider mower blades to an edge between .020" and .030" The more rough work it does, the thicker the edge. Probably would apply in your situation. Disc position to help control the heat is needed when you are getting in there to do some serious sharpening. Or use flap discs, but you will go through more. Balance when your done.

 

[mikester]

Painted blades can appear dull. Typically I will sharpen rider mower blades to an edge between .020" and .030" The more rough work it does, the thicker the edge. Probably would apply in your situation. Disc position to help control the heat is needed when you are getting in there to do some serious sharpening. Or use flap discs, but you will go through more. Balance when your done.

I second this. I just put on new blades and the new ones are sharp.

I keep mine sharp. When the mower can稚 keep up it tells me it痴 time to scrape the deck and sharpen the blades. I take my blades off and sharpen them using an 80 grit flap disk on a hand grinder. I try to keep the original blade angle and leave a clean, very sharp cutting edge.

I don稚 need to resharpen every time. What kills the edge is hitting clumps of dirt, hidden rocks or branches.

Dull blades leave a ragged cut edge on the grass, more like tearing vs cutting. Sharp blades cut and mulch the swarf better. I find dull blades leave more cut grass clumps.

 

[JerryK]

Up here in Michigan, sand is the culprit in dulling blades. A normal high lift blade vacuums up anything loose and the sand slowly even makes the uplift portion of the blade to disappear. You can run sand blades, those that have no uplift, and the will stay sharp all summer. But the normal uplift blades dull fast.

 

[mcfarmall]

Up here in Michigan, sand is the culprit in dulling blades. A normal high lift blade vacuums up anything loose and the sand slowly even makes the uplift portion of the blade to disappear. You can run sand blades, those that have no uplift, and the will stay sharp all summer. But the normal uplift blades dull fast.

Right on, Jerry! I've had to repair holes in lawn mower decks that were caused by sand abrasion...the metal gets blasted so it's as thin as foil then it blows through.

 

[mikester]

Right on, Jerry! I've had to repair holes in lawn mower decks that were caused by sand abrasion...the metal gets blasted so it's as thin as foil then it blows through.

I’ve got sandy soil but I go for the high lift the get the dandelions. Nothing more frustrating than the dandelions laying flat then simply popping back up after I’m done mowing.

The gator blades lasted a long time with the sand blasting but they didn’t do well with the dandelions.

 

[Oldtink]

I think the slightly dull approach is better. It doesn’t take long for the razor sharp blades to dull worse than you started with. And I’m not in the sharpen blades forever crowd. After a couple sharpening the square edge is gone and cut quality suffers.

I agree. Got to maintain that square corner at the tip and in order to do that often requires a lot of metal down the cutting edge has to come off too. While 30 degrees is the industry standard for the cutting edge, a 35 degree or so will leave more support metal behind the cutting edge and give you a tougher cutting edge. Eventually it's just not worth the effort with all that grinding, watching not to over heat the cutting edge etc.
View attachment Blade geometry.pdf

 

[oosik]

I think it kind of depends upon what you will be cutting. My "lawn" is actually field grass/meadow grass that has been mowed, now, for 36+ years. Its become quite thick and lawn-like looking. I have the same OEM blades on my 2003 JD G100 mower. I "sharpen" them in the spring and that's it for the year. Actually, its more of a process of removing the large nicks, dings and boo-boos and balancing the blades. Another three weeks and everything will have dried out and died for the summer and my mowing for this year will be over again.

 

[hslogger]

What ever your angle and preference may be, sharper mower blades will help lessen the burden on your motor and belts, especially in thick and or tall material. That is not even taking into account the visual end result.

I have a friend that bid and awarded a rough mowing contract when he was beginning business in the eighties. All he had was JD small diesel tractor and a four foot brush hog.
He sharpened the blades on the brush hog after each very long day of running this set up through some of the "rural feel" parks. The municipal client always used this guy's results as the requirement in future contracts with him and other providers.