Another Question Concerning Blade Sharpening

Discussion in 'Lawn Mowing' started by MOturkey, Oct 6, 2012.

  1. orangemower

    orangemower LawnSite Silver Member
    from pa
    Posts: 2,773

    You can make claims like this all day long but others that know better will think you're dumb. I can't see how blades would need sharpened daily if they're sharpened correctly.
     
  2. If you cut a lot of properties per day, you prob need to sharpen daily.
    Posted via Mobile Device
     
  3. PlantscapeSolutions

    PlantscapeSolutions LawnSite Silver Member
    Posts: 2,979

    Are you talking about the Scag type blades where they cut lower at the tip then they do at the part closer to the spindle?

    The thing I have noticed is the Oregon Gator blades are flatter on the top so they sharpen more easily. The J Thomas version of the blades is not flat on the top. I have the more expensive Magna-Matic for mulching blades but I think you could use the cheaper version on the Gator blades without a problem.
     
  4. Ridin' Green

    Ridin' Green LawnSite Fanatic
    Male, from Michigan
    Posts: 13,286

    I believe he's talking about blades like these below. The wave varies by manufacturer, but the idea is all the same. These are Deere OEM wavy mulchers for use with their mulch kits for their Z's, and I used these on my Z950 60" MOD just today on leaves and they work excellently.

    100_1632.jpg

    100_1636.jpg
     
  5. Greg78

    Greg78 LawnSite Silver Member
    Posts: 2,010

    I'm talking about the wavy blades like Ridin' posted. I sharpen wavy blades with my Bradley blade sharpener just fine as the top part of the wave doesn't dull as much as the flat lower tips do so it only needs touched up lightly.

    I've had the terrible results mulching with Gator blades.
     
  6. PlantscapeSolutions

    PlantscapeSolutions LawnSite Silver Member
    Posts: 2,979

    My Scag SWZU's came with blades just like that as part of the Hurricane Mulching Kit. I used them for a while and went back to the Gator blades since they were easier to sharpen.

    The whole logic behind the wave type blade is to have the inner part that's moving move slowly (blade tip speed) do less work by cutting less. While the lower section of the blade really does all the work.

    I miss the old square style Scag decks that were much more mulching friendly. I call the Advantage deck the Disadvantage deck for guys like myself who mulch.
     
  7. Ridin' Green

    Ridin' Green LawnSite Fanatic
    Male, from Michigan
    Posts: 13,286

    That's not correct, at least as far as regular wavy mulching blades are concerned. It may not be that apparent in my pics, but the inner section is higher than the outer section of the cutting edge, The outer section has all the lift built into it, and the inner section actually is just the opposite. It has a built in downward slope to the rear edge of the blade from the cutting edge. The outer section's lift fin is tapered down towards the lower rear section of the blade, and slightly bent inward at the tip to cause lift, followed by moving the cut clippings in towards the center section, where the higher cutting edge re-cuts them and then sort of scoops them in and drives them downward into the turf.
     
  8. PlantscapeSolutions

    PlantscapeSolutions LawnSite Silver Member
    Posts: 2,979

    Those are the exact blades my kit came with. I see what your saying. What I'm basically saying is the closer you get to the blade tip the more cutting action is taking place and the more the blade is working. By the time any grass get to the inner blade section it has been cut a bunch of times. But there could still be some finite number of blades that get skipped as they pass under the center section of the blade but as they pass towards the rear of the deck the outer (lower) section of blade cuts the grass again.

    The Honda commercial push mower has much better logic in using one upper blade for re-cutting the clippings. The Honda uses a full length upper blade for greater blade tip re-cutting speed. The wave type blades really do not have much re-cutting power on the inner section of the blade because it is moving at 50% or less of the speed as the actual blade tip.

    You could probably grind the edge off the inner (taller) blade and make it totally blunted and not see much of a difference in clipping dispersal. I may dig out my Scag wave blade and do a few experiments.

    I'd like to try a mower that has blade timing to see if there is much of an improvement in minimizing mohawks when cutting taller grass after a growth spurt.
     
  9. Ridin' Green

    Ridin' Green LawnSite Fanatic
    Male, from Michigan
    Posts: 13,286

    It is true that the inner edge of the blade is not cutting any standing grass since it has already been cut by the lower cutting edge first. The upper cutting area is mainly to re-cut the flying clippings a few more times before they are driven into the turf by the rearwards slope of the blade behind the upper wave area.

    I don't now if I can explain this so that it makes sense, but think of the shape of the blades cutting area, both inner and outer as a doughnut lying flat on a table top. Now think of the outer section of the blades cutting area as the doughnut tube itself. The air in that area is constantly swept upwards and inwards by the shape of the lift sail. The inner area of the blades with the higher cutting area would represent the doughnuts center, or hole. While the doughnut is round while lying on the table, the doughnut's "tube" is also round in shape itself. That represents the airflows direction or turbulence. So, while it is spinning in a latitudinal circle, the air is also flowing in a circle longitudinally from the outer end of the cutting edge, inward towards the center where the higher part of the blades wavy edge re-directs it downward. The shape of the blade isn't so much for extra cutting ability, but to move the air in a way that re-circulates the clippings over and over keeping them flying past the entire cutting edge of the blade until the pieces are so small and have so little mass left that the suction of the lift fin can no longer lift them to be re-circulated,and the downward force of the inner hump drives them into the turf.
     
  10. MOturkey

    MOturkey LawnSite Silver Member
    Posts: 2,746

    Well, of all the replies in this thread, yours is the only one that actually addresses the original topic. :) Thank you for that. It is also good information to know.

    I'd still like to know though, if sharpening, over time, will soften the metal to any appreciable degree, even if you don't overheat the blades?
     

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