Dull Blades

[Bob_Bainbridge]

I just ordered third party replacement blades for my Toro push mower and Cub 54 inch deck. They came from two different suppliers. The Toro blade has a pretty good edge on the blade but the Cub blades have a rounded edge and you wouldn't be able to cut yourself with the blade even if you tried. Is this normal?

Bob B.

 

[Thomas]

I haven't yet to get set blades as such,was there any info in box etc. about the blades?

 

[ChuckT]

I've seen that some blades are sharper than others when new but never with a rounded edge.

 

[Gary Fowler]

I just ordered third party replacement blades for my Toro push mower and Cub 54 inch deck. They came from two different suppliers. The Toro blade has a pretty good edge on the blade but the Cub blades have a rounded edge and you wouldn't be able to cut yourself with the blade even if you tried. Is this normal?

Bob B.

I would send them back. I have never seen a new set of blades that were not sharp on the edge. A dull blade will take more HP to push thru the grass and make for a ragged cut also. You aren't running a bushhog whose blade may have a 1/8" or larger edge on the blade but that should never be the case for a finish mower or lawnmower blade.

 

[the old grind]

Depends on what you call 'rounded'. In the trade we call out a tool bit corner radius that may be as small as .015", or equal to a .032" (20 Ga) wire. We don't always want to put a razor sharp edge on such blades because they round over too easily and may do so until more obviously 'dull'. While I hold a much smaller standard to sharpen, many new blades will come with, or makers recommend to sharpen with, a .015-.030" 'blunted' edge to prevent just that. btw, Sharpening to a 'feathered edge' is a waste of part life.

The first time you sharpen your blades, that initial grind will be pointless. If you don't sharpen your own blades, compare taking them in for a 'grind' to sending them back and perhaps getting sent the same thing a second time. btw, I sharpen just about everything, tho' no longer straight razors or medical scalpels, and wood turners 'hone their own' or would give up the hobby. I don't charge to play. "Bring me all you got." Make sparks, Boys!

 

[RandyT]

Oregon, worlds largest lawnmower blade manufacturer has a 30-30 rule which means blades are ground at a 30 degree angle and leaving a .030 blunt edge. No reason to go thinner than that on the cutting edge since the first mowing will normally a sharp edge to that dimension anyway, so removing more material than necessary is just a waste.

 

[ChuckT]

When I had a SCUT (Yanmar 1510D) I came upon a long discussion that, summarised, don't sharpen to a knife edge, use a 30* angle, a 1/32" edge and keep your RPMs correct (that number escapes me). What you are wanting to do is to chisel off the grass blades not whittle them.

 

[Oldoak]

What you are wanting to do is to chisel off the grass blades not whittle them.

That may be true with bush hog blades, but I want a sharp, clean cutting edge on my lawn mower blades. However I do consider a 1/32" cutting edge to be a "sharp" edge. Anything more than that is too blunt for lawn mowers.

Professional grounds keepers will tell you a ragged cut on lawn grass blades can lead to stress and diseased lawns. That's why most golf courses use reel mowers to cleanly sheer the grass rather than hack it off.

Edited to correct spelling.

 

[ChuckT]

Ok, shear rather than chisel.