Rotary Cutter Sharpening Rotary Cutter Blades

[YardBikeBob]

What is the prevailing wisdom (oxymoron?) on sharpening the blades on a rotary cutter? Yes, there is a pretty good 2-year old thread on this.

It was time to mow again and I noticed the tips of growing grass looked more bludgeoned than cut previously. Time to look at the blade.

It looked awful. So I dragged out the 4 1/2 angle grinder and went after it. I left the blades on the cutter and just worked them over from the back of the implement. A half hour of effort including finding an extension cord. I was amused that the 'spec' is a 1/16th edge -- like me and my grinder could hold to that.

It did mow a lot better. The grass was a foot high and the tractor went through it like a hot knife through butter. Unfortunately, humans are creatures of habit and/or stupid and I started at the periphery of the field and worked inward. The edges of the field is where the rocks grow better. So by the time I got to the 'pretty' part of the field, the blades were dinged up again. OTOH, if I could be more careful, that 1/2 hour of effort got demonstrably better results.

Before the sharpening, the blades were so banged up I'm surprised they cut at all. That must be a lesson in what a heavy metal blade with the cutting edge like a chunk of rebar will do at 200mph.

Bob

 

[boggen]

razor knife sharp = no good
knife sharp as in (pealing knife in kitchen sharp) = no good
butter knife (blunt edge) = getting there but not yet
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dull = rounded / oval shaped

for me something a tad more dull than a butter knife.
1/8" or perhaps a little more.

rotatory cutters (bush hogs = name brand) take a beating, whacking out smaller size trees, to hitting rocks, to scalping the dirt (blades running into the ground it self), to hitting dirt clods.
you won't be getting a "golf course" cut, let alone a lawn / yard cutting. they are setup / made, for big stuff, and as a result give a much rougher cut. as in "splintering" and "ripping" vs actually cutting stuff in half like a finishing mower.

you don't want a "long" taper down to cutting edge. say 45 degrees top and bottom coming to the blunt edge of about 1/8" this way when ya do hit a rock. it just gives a little nick, vs taking out 1/2" plus of cutting edge.

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some folks want super clean cut like a finishing mower, and will spend the time constantly sharping the blades, to point of even using the rotatory cutter on the regular yard/lawn. in those cases sharpen the blades up like a finishing mower blade.

yes a sharper cut does require less HP from tractor, but the trade off any rocks, larger thicker / taller weeds will eat the cutting edge up.
yes a duller edge does require MORE hp from tractor, but less sharpening, and can take more of a beating without constantly re sharping the blades.

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like finishing mower blades, it does help if you pull blades off and "balance" the blades. so they are the same weight, and will balance out level from end to end. balanced blades = less wear and tear on stuff, and more likely a easier cutting and better cutting.

 

[nybirdman]

You want to shatter not cut,cutting you end up with a bunch of "pungie" stakes.Not good for tires or people or pets.

 

[Gary Fowler]

You want to shatter not cut,cutting you end up with a bunch of "pungie" stakes.Not good for tires or people or pets.

I do believe he said he was mowing grass, not saplings. If mowing just grass, a sharp blade will work and cut much cleaner than a 1/8" thick blade that is standard for bush hog. It will not deal with rocks very well though. If I were just mowing grass, I would put a 45 degree bevel on the blade and put a sharp edge on them. They will get dull faster but at least you start with a sharp blade for easier and cleaner grass cutting. I would remove them from the deck and balance sharpen them because you will be taking off a lot of metal to get that edge on them.
I have been contemplating doing that with my bush hog as I no longer have a need to mow down trees.

 

[mikehaugen]

like finishing mower blades, it does help if you pull blades off and "balance" the blades. so they are the same weight, and will balance out level from end to end. balanced blades = less wear and tear on stuff, and more likely a easier cutting and better cutting.

I have always wondered what everyone's procedure is for doing this. My woods finish mower has the "swinging" blades similar to a rotary cutter and I one time actually took the time to take each blade half and set one end on a block of wood and the other end on a kitchen scale (measured grams) in both directions to make sure each pair was close (within a couple grams). It worked well but sure was time consuming. I don't use that mower anymore and the rc doesn't get balanced... just wondering how you guys balance the two piece blades.

 

[boggen]

I have always wondered what everyone's procedure is for doing this. My woods finish mower has the "swinging" blades similar to a rotary cutter and I one time actually took the time to take each blade half and set one end on a block of wood and the other end on a kitchen scale (measured grams) in both directions to make sure each pair was close (within a couple grams). It worked well but sure was time consuming. I don't use that mower anymore and the rc doesn't get balanced... just wondering how you guys balance the two piece blades.

i have been known to raise deck up / block it up, and grind away.
if i start it up with deck raised, and it sounds like a helicopter and deck is vibrating. then i am in trouble. and moan and complain, because i should of taken time to just pull the blades off and balance them.

honestly i haven't sharpened rotatory blades in some time, hasn't been a real need to. just haven't used it.
with that said, at one time i remember seeing a "router" bit perhaps grinding bit that resembled something like a pulley. to make quick work of putting cutting edge on to rotatory cutter blades. for what i remember it could have been a drill bit, with a pulley shape grinding head on it.

 

[BlacknTan]

Yeah,

funny how those rocks seem to grow, and reproduce on their own... More prolific than rabbits!

 

[Mud Mechanik]

I have always wondered what everyone's procedure is for doing this. My woods finish mower has the "swinging" blades similar to a rotary cutter and I one time actually took the time to take each blade half and set one end on a block of wood and the other end on a kitchen scale (measured grams) in both directions to make sure each pair was close (within a couple grams). It worked well but sure was time consuming. I don't use that mower anymore and the rc doesn't get balanced... just wondering how you guys balance the two piece blades.

I take them off of the cutter and sharpen them pretty sharp ( I am only clipping clean grass ), then I use a fish culling board to see which one is heaviest.

 

[HEC]

I have a 6 ft. bush hog squealer over 20 years old and I sharpen the blades pretty sharp on the cutter with a grinder every spring before mowing down 30 plus acres of old hay fields . I have never taken them off to balance and the cutter runs just as smooth as it did when new , and I do hit a rock or two each year .

 

[rsallen]

I always try and keep the original angle of whatever the blade was when new.
The blades (two different mowers) measured at 32 degrees new if memory serves. Yeah I keep at least a couple of sets for each mower so if I don't like the cut I can swap them out without making a big deal of it and sharpen at my leisure.
Made my own balance device from a super fine free wheeling bearing I came up with from some place or another, clamp it on to the bench slide the blade on and touch the blade...if it's out of balance the heavy side stops pointing down. Balanced blades sure make it easier on those carriage spindles.

I hate grass.