OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Walk Behind Lawn Mower Frames Victa Lawn Mower Frames How Sharp should the blades be?

I just replaced the 4 cutting blades on my 4 yr old Victa Hawk (BS475 engine) and noticed the new Victa blades aren't very sharp.

How sharp should the blades be? There are probably safety issues to consider but are there any rules of thumb here? Should I be sharpening them on the grinder prior to installation?

Cheers

gcv

Not terribly sharp, the second you use them a razor edge would get knocked off anyway.

I believe that sharpening the blades for a rotary mower is one of the biggest Urban Myths in existance. I've had many people ask me the same question. Velocity is what makes the blades cut. Grinding the blade edge only serves to shorten blade life.

I can remember seeing many agricultural slashers that use lengths of high tensile chain as the blades.

I'm not convinced, Greg. I used to buy blunt blades and use them as-received, but they would not cut one particular kind of "grass" that consists of very small diameter cylindrical blades that grow one-per-plant from a largish underground nodule. Sharp blades will cut that stuff, and if you keep it cut, it doesn't seem able to compete with the real grass, so it goes away. I've been using sharp mower blades ever since.

Incidentally my slasher (a 5 foot offset contractor type with a 70 hp Hadbro gearbox, I don't recall the brand of slasher, but it was one of the 2-3 serious local brands) had sharpened blades, and it is just as well, considering they were half inch thick spring steel, two inches wide.

I agree that you can do most mowing with blunt blades, but you can get a neater job with less blade speed (and therefore less machinery wear) if you use sharp ones. Ordinary push-mower blades can be resharpened with a hand-file in mere seconds per blade, without removing them, if you maintain them. For me that means a touch-up about once per 2 years. If you tend to mow a lot of rocks, it all becomes more of an issue though.

I think you are talking about onion weed by the sounds Grumpy.

Silver grass is another tough one to cut.




Im a bit hot and cold on the sharp blades thing.
How thick is the steel, 1-1.5mm spinning at 3000+RPM, im not thinking it need to be razor sharp to do the job.

It was indeed onion weed, Bob. When I switched to sharp blades it seemed to go away over a couple of years. The sharp ones cut it, the blunt ones didn't.

If you are mowing something like couch or kikuyu, or even fine rye grass, provided you run the mower fast you can get an OK result with blunt blades. My theory, though, is that the less you shred and tatter the cut ends of the grass, the better the job. Also, when I'm mowing easy stuff, I like to use about 2,500 rpm, and save the flat-out stuff for when the wheels really sink into the longish kikuyu in summer.

Yes I do agree! Onion Weed or Onion Grass is one difficult obstacle, then yes, the sharper the better. Other than that, I stand by my statement! May I state that Onion Weed, or Onion Grass, is not grass! Correct me if I'm wrong Grumpy, but the discussion was about sharpening blades, NO mention of cutting Onion Weed / Grass!

I have made several blades for mowers out of 3.0mm thick spring steel, and never have I ground an edge of them. They have, and still are, cutting fine!

And yes, Onion Weed / Grass as well! The way I see it, that stuff, along with Bathurst Burr, Paspalum, Patersons Curse, and other NOXIOUS WEEDS should be removed from existsance anyway!

I agree that onion grass/weed is a weed Greg. I find it isn't very convenient to remove it from a grass area by spraying it though, since it is moderately resistant to glyphosate and you end up with a whole lot of 1.5 inch circles of dead grass all over the place. I also agree that, at least in my experience, you can mow real grass pretty effectively with blunt blades - but I think you can come closer to the reel-mower ideal by using sharp blades.

Having had issues with my last lawn, and some of the various species that grew very happily amongst it, I found it was a mix, in general, the sharpening I did was to keep the blade straight more than anything, and to bring the edge down to about 0.7mm.

I never found going past about .7 or .6 had much effect, as it wore off faster, and really did not show a huge effect on the lawn, however, once the blades wore back to the thickness of the metal, or even much greater than .7, I found i was having to double take a fair bit of the lawn.

OK
There seems to be a bit of varied discussion here. I'm going to experiment. I'm going to use the dull (new)) blades as they are are for a couple of mows then sharpen them and come back and give you my impressions.

I have a many different kinds of grasses and weeds in my lawn (trying to spread the buffalo though) so it should be a good test.

Cheers

gcv

I shall be awaiting results with interest - just purchased new blades for the slasher and was surprised to see them to be so blunt with about 1mm of vertical attack edge - but then the whipper snipper works with 2mm cord

I'm quite curios too, as the topic seems to have many different experiences to it.

Awaiting your results eagerly!

OK, the verdict is in. After a little experimentation I noticed no difference between cutting standard length grass of various types with new blades, good sharpened blades and finally blunt blades.

Where I noticed a difference was in mowing down hedge trimmings. The new and sharpened blades worked equally well, where the blunt blades were not as effective. The new blade's quality in cutting lasted longer than the sharpened blade

A new blade has two 90 degree edges very close together (top and bottom of the cutting side). A sharpened blade only has one sharp edge.

Maybe if there is a way to sharpen the blades so that it has two edges on the cutting side, like a new blade it would be best. You're nto aiming for a knife styled edge. Rather, a rectangular edge with two keen 90 degree edges close together.

Now, back to that stubborn trimmer that dies when revved.............

gcv

gcv, good testing mate, I had pondered the same question once, grumpy's comment about a cleaner cut on the grass blade is what I found and at lower rev's too. On fine leaf buffalo it doesnt shread or feather the end of the leaf so much so then you dont get as great a "brown" tip effect in a few days. It will be interesting to see if you notice any difference over the nxt few days / week of the various blade types.

I'm going to chime in here....

As taken from my shop manual:

"Cutting blades on a rotary lawn mower should be sharp enough to cut grass without tearing, tearing causes tops of the grass blades to become brown, it also makes grasses more susceptible to diseases, fungus and blight"

And from another part of the same manual:

"A sharp blade or cutting disc reduces drag on the engine,saves fuel,and extends life on both the engine and blade"


Hope that answers your questions.

Kori

Good points about the tearing & engine wear.

My blades tend to sharpen themselves over time to thin sharp curved blades!

It must be that cement lawn edge that keeps them honed.

New blades always get a zip on the grinder wheel. I'm cutting grass not dirt so two sets of blades should last the life of the mower.

My Mustang is 30+ years old and is only on it's second blade set...

... as it only does a tennis court, grass path and a front lawn but it has done these over 800 times without an issue so far!