Reason for Dull Mower Blades?

[SteveHGraham]

Yesterday I detached the deck from my lawn tractor so I could check and sharpen the blades. What a mistake. I gave the manual the benefit of the doubt when it made it look easy. It took forever, and I had to use a farm jack, an impact wrench, bricks, and a three-foot pipe wrench. Unbelievable. The people who write manuals should be tied down and mowed.

Anyway, I read online that John Deere mower blades should have a 0.4-mm flat cutting edge on them, which seems really stupid. That's about like the edge on a ruler. I used a belt grinder to make them considerably sharper than that.

Can anyone think of a reason to have dull mower blades? I have bahia grass, and it's very tough. Dull blades don't get it done.

[John Hasler]

They probably think that you are mowing a suburban lawn and want to "mulch" the cuttings.

[tornitore45]

I used to move 2 acres in Sarasota, the lot was basically sand and the sharp edge would last a couple of times. The blades were replaced for being thinned down by abrasion before being ground too far back.

[spro]

I agree that the blades' sharpened edge is tailored to expected lawn. There is nothing duller than a sharp edge which has been folded back. 4mm seems excessive to me. I do 1.5-2 mm but it isn't the same tractors. Before getting lost in the weeds, there is reason for seemingly dull edges. You experienced the hassle of sharpening them.
Mowing tractors' operators need to know the area. There is a root or a brick which will immediately take out the sharper edges. Then they are more useless than a dull one. Not all garden tractors can propel a 3 blade deck of 48" -60" reliably so the blades are sharp.
The deal is that, yours is more powerful. You can hack that stuff and know the killer areas. The whole time it is hacking, it is becoming sharper. That's the way it works. Sharp blades become dull and semi-flat edges become sharper.

[cmitcham]

I don't know, so i'll listen to the john deere engineers. I do know that when I remove my blades to sharpen, a 0.4mm edge is very sharp compared to what I start with. guess I'm not to careful about what I hit

[spro]

Maybe I'm going blind but I didn't see the decimal in the original post. >.04 MM is only .016" so I responded in kind as 1.5-2.0 MM and certainly they sharper than that. The cutting edge needs the blade angle to be ground back to meet it. That is where blade balancers come in.

[spro]

Older stuff, old blades resemble scythes. They have been sharpened and ground back so many times.

[SteveHGraham]

At least I know the reason now. But I plan to keep my blades a little sharper than that. They just were not cutting the grass.

[earlgo]

I always sharpen my mower blades to a sharp edge. But then again, the "lawn" here is mostly weeds and moss that the blades don't touch. I've never seen a rolled edge except for a rock hit. I also always balance the blades even though the old Craftsman 44" deck wouldn't know the difference. The 3 blade set is changed out twice a summer.

I thought one only had to drive the JD over the deck to hitch it up, at least that is what the ads on the telly show.
--earlgo

[spro]

They also say affordable. I Like that grinder.. I do mine free hand but balance causes more touch up.

[John Hasler]

earlgo writes:
> I always sharpen my mower blades to a sharp edge.

So do I, but I grind back the flat side slightly to reduce the angle of keenness.

[spro]

In theory, you shouldn't do that. They are looking at mower blades as plane blades. Reality is what works for the job but losing the flat reference invites trouble. When grinding the actual cutting angle, it will have to be ground back further. The blades are shaped to expel the chafe over top and exit quickly. A hatchet grind leaves more driven downward. That is useful at times but in the long run, the cutting edges should be parallel across the deck. It is akin to cutting in line to the previous cut and not starting a new one. Wait a minute, I've been there. No matter how sharp, each blade's edge should strike at the same point and they should be in close unison to each others' level.
Sure that is easy to say and why it comes to evacuation. Underpowered or under designed mowers need all the help when tackling 2- 4' stuff. There is a Load coming out the chute and any obstruction blocks it. There is sort of a wind tunnel going on inside the deck and heavy trails of grass/etc coming out. Those rows are easier to dispose of than a thatcher later.