Blade questions Again!!!

Discussion in 'Lawn Mowing' started by jcltyson, Apr 6, 2006.

  1. jcltyson

    jcltyson LawnSite Member
    Posts: 97

    I know the blade subject has been beaten to death (sharpening and stuff), however I can't find where anyone covers the question at what point do you say thats enough....time to toss this guy, no more sharpenings...?

    Do you have a particular number of times you sharpen, or are you looking at some physical point on the blade surface you are gauging by..?

    Care to share your thoughts on this subject?

  2. MJLsLawnCareNmoreLLC

    MJLsLawnCareNmoreLLC LawnSite Senior Member
    Posts: 841

    Generally depending on the width of the blade, after about 1/2" to 3/4" has been removed the blade gets tossed.

    I wouldnt go by number of sharpenings because it depends on who is sharpening and how much material is taken off.

    Besides blades are cheap. No sense in re-using blades over and over until they become unsafe.
  3. jtkplc

    jtkplc LawnSite Silver Member
    Posts: 2,646

    I just eye it and judge by how much material has been taken off and by how beat up the cutting edge is.
  4. topsites

    topsites LawnSite Fanatic
    Posts: 21,653

    Me, too ... But:
    - I run the weakest (oldest) blades on my old(er) machine, I run the meatiest (newest) blades on the new mower (it has a lot more power and rpm). This is to prevent fly-apart from happening, and it helps to run worn blades on lower rpm stuff. Also, the new mower gets the new blades, then once worn to a point, I got blades for the old mower - The old(er) mower sees a lot more off-turf stuff, I'll take the old one through the rough a lot faster than the new one, and I'm not afraid of replacing a blade if it gets bent (since it's worn anyhow).
    - I check the mfg's recommendation (it's fairly ridiculous, it's hardly worn but I can see their point - guaranteed not to fly apart). I usually go twice that amount of wear, but I also make a small grinder mark at the replace NOW point (I make this mark on one or the other side when the blade is out of balance, so it serves a double purpose: restores balance, and gives me the end-of-life guide). Obviously, once the mark is made...


    Far as blades being cheap, I don't know but 70 dollars for 6 of them is more than I'd like to pay.
    I'd show you one but I'm not in the mood to take pics, and it's downstairs.

    Just make sure you don't run them until they're slivers... I've seen that, and it just baffles me how anyone could do that.
  5. TLS

    TLS LawnSite Fanatic
    Posts: 7,937

    The further you sharpen a blade back towards the lift wing, the SHORTER your blade gets in overall length.

    This is why a fully sharpened old blade cuts like crap compared to a brand new blade.

    Usually when they start to get old, they get ruined by a rock or something that prevents them from being used anyway. I'm a blade freak. I have probably 25 sets of blades in my shop.
  6. topsites

    topsites LawnSite Fanatic
    Posts: 21,653

    Do the outer edges of your blades angle inwards? I mean, can you see this happening, and have you taken old and stacked them on top of new to see?

    Because mine don't angle, and they don't shorten. Ok, yeah, they do, maybe by a 1/16th of an inch from front to back, if you add both sides together you might lose 1/4 of an inch on a rainy day.

    The biggest thing is fly-apart, you don't have enough steel left on a worn blade to keep it from coming apart at 3000 rpm, especially if you hit something, it is possible a sliver or chunk of steel come flying off. Nevermind it throws your mower off balance, but that piece of steel, who knows where it will land, huh...

    Other than that, this is an old wive's tale in my book. Of course, I have seen the fools who, when sharpening, must take off a considerable amount of steel. I mean, if you sharpen to where your outer edge no longer exists, you've already gone several inches beyond mfg. specs. and are far beyond where I throw them away, and you're in serious danger of finding out what fly-apart means.
    I only go over it twice real light, just enough to restore the edge, it's not even enough to take out burrs or nicks (they just have to work themselves out over time). I can easily sharpen a blade 100 times before it needs replacing, that's how little steel comes off.

    I would take pictures, but am still not in the mood.
  7. TLS

    TLS LawnSite Fanatic
    Posts: 7,937

    No wives tale here...

    Take a tape measure, turn blade upside down on workbench, measure from blade TIP to opposite blade tip. This will be a diagonal measurement.

    In addition to this measurement getting smaller, your angle of attack starts angling back and is no longer 90 degrees.
  8. topsites

    topsites LawnSite Fanatic
    Posts: 21,653

    Ok, I see what you're saying and I do believe that makes a small difference. I thought you meant people who sharpen them beyond the back edge, to where it is visibly shorter from side-to-side, lol

    Anyway, I took some pics, both a new and an old blade. The new blade is slightly worn but it was brand-new 3 acres ago, it barely has a day of use in it, has never been sharpened and the paint just wore off the edges.
    The old blade has been sharpened well over 100 times, is in use only on the older machine and has gone through well over 1,000 yards.
    The old blade is just now past manufacturer recommended replacement, thou I run them longer because when the old mower goes through the rough, nothing beats an old blade.

    To run the old blade is technically wrong, but I run them on my old machine. Should you run them? I can not tell you what to do.

    The white arrows point to the fly-apart spot: This is where the steel is at its weakest on this type of blade, but all blades have a weak spot and as one sharpens them, the weak spot becomes thinner.

    The second picture the old blade is lying on top of the new, thou honestly speaking, it is not really shorter as far as I'm concerned, the angle is not a perfect 90 degrees but it's still close (what are we talking here, 89.5 degrees? I mean, it's almost 90...).
    To maintain the angle, notice how I came in from the inside of the blade and worked my way out over time, this is not without thought.
    But yes, the new blade does cut slightly better, to a very small degree .... Anyway:
  9. rodfather

    rodfather LawnSite Fanatic
    Posts: 9,501

    I toss em when the tips start rounding off badly.
  10. topsites

    topsites LawnSite Fanatic
    Posts: 21,653

    Ooops, I noticed something else after the 10-minute time-out.

    On the second picture (I put it here again, with an edit), the arrow points to that small mark that I make with the grinder to mark the spot when I will replace them, thou this is deep in the red danger zone and you take your chances with fly-apart.

    This blade only has one mark, I usually make the mark when the blade is off-balance so as to both get the blade marked and the balance restored. To see the mark, you have to look close, but it's there, about a 1/4 inch groove at the end.

    Technically yes, the old blades should be tossed, they are past mfg. replacement specs.
    But I ain't running my new stuff through the rough, and the old blades still cut decent, too.


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