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.

 

[cisco]

Seems most around my way don't sharpen the blades on their rotary cutters, but then again they don't use them on lawns. The guy I most often cut stuff with, a hunting club buddy, hasn't sharpened his since buying the unit used a decade ago. Whatever.....I sharpen blades the "quick and easy" way, i.e., laying on my back under the cutter (with safety wedges) with an angle grinder, once or twice a year depending on cutter use and what I've inadvertently hit with it. I used to take off the blades and fine tune them on a grinder (modestly sharp edge - like when new) once a year when I was clearing saplings and heavy brush, but now every 2 years as it's now mostly weeds and light brush, and every few years I'd buy new blades. Yup, with a tractor 15 HP lower than my friend's I could cut everything he could re. saplings, and when I trimmed the weed-filled edges of roads the stuff didn't look totally mangled behind my cutter's sharper blades. Now, as to balancing it's a challenge given the blades weigh ~ 23 lbs each (Woods 72 behind K L3400), and one has to get the blades within an ounce or so if one doesn't want major vibration and cutter spindle stress. Couldn't use my kitchen scale with its' 15 lb limit, so went the route of Solomon - an 8' bar (straight 2X4' in my case) with hooks at each and a U-bolt at its' midpoint - would suspend bar from garage hoist, place a blade on each end and then just watch how it balanced out.
So, big tractor and only brush/saplings - sharp blades not critical.....for smaller tractors or fine weeds and grass, then it's quite useful.

 

[YardBikeBob]

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. I have been contemplating doing that with my bush hog as I no longer have a need to mow down trees.

Thanks, Gary, you're a careful reader. The first few years of owning this place we didn't own a tractor. All I could do in the meadows is cut some trails with a Swisher behind my ATV. When the tractor came along, I had the perfect justification for a rotary cutter.

Now we've trimmed out a piece of the meadow, all of the small trees, saplings, and blackberry patches have been beaten down and now it is just mowing grass.

Sharpening the blade did a much better job just cutting grass. Now if I will just quit trying to expand the area I could quit scalping rocks and dinging the blade again.

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.

There ya go! Letting me know I'm trying to use the wrong tool for the job. The TBN trademark! Go buy another implement -- a finish mower! It would seem, to do it right, you only need the RC the first time to knock down the area then maintain with a finish mower.

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Thanks for all the feedback. I am happier with the RC performance with a sharp blade just cutting grass. I was just wondering how often others sharpen their blades. Never? Once a season? More often? I'm thinking I might run the blades past the angle-grinder a little more often if I'm just working the grass. The performance was better.

I'm still in awe of the amount of violence there must be under that RC deck as it still cuts when the blade is so dinged up.

Bob

 

[YardBikeBob]

Now, as to balancing it's a challenge given the blades weigh ~ 23 lbs each (Woods 72 behind K L3400), and one has to get the blades within an ounce or so if one doesn't want major vibration and cutter spindle stress.

Wow. Balancing within an ounce on something weighing 23 lbs? Don't they have OCD medicine for that?

So far, I'm thinking if I'm grinding a few minutes on each blade, I'm sorta balancing the blades as I go. And, no, I really don't want to bother taking those blades off and trying to retorque those huge bolts on the RC cutter.

I'm still using some 2-stroke Lawn Boy push mowers from the 70's around the yard. (Nothing smells better in the morning!) Sharpening those had been the only time I've noticed balancing would make a difference as their blades are thin, stamped steel. And then I just replace them once I hear the 'helicopter sound'.

Bob

 

[YardBikeBob]

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

Huh. So you Yankees have rock gardens, too? It really is amazing how they sprout in the Spring. The north end of this state, above the river, is almost all clay soil. I personally know people who have purchased rocks to meet their landscaping goals! And I'm saying a few Benjamins per rock! Go Figure.

Of course, if I could find a decent deal on a load of real top soil. . .

Bob

 

[rsallen]

For me Bob I found I saved quite a lot of time by using a dedicated mower as opposed to a mowing deck on the tractor. Some years ago (15? 20?) I got a reasonable deal on a Groundsmaster and never regretted the decision, over all it easily cut my time spent mowing by more than half what it used to take.
I kept the old deck for the heavy garbage I was reclaiming from the wild for a few years and was using it less and less as time went on. Finally sold it to someone that wanted to do the same thing with it as I had started with it. Good old deck, it was old when I bought it, Woods 6ft deck, and a heavy mother. Worked nice considering what it was.
One day driving down the road I noticed someone had put an older Scag 52in finish mower out on the front lawn with a for sale sign on it. I thought well at least look at a zero turn I got no place I need to be. So I turn around.
Sale was right. I bought it for $200, a couple of belts and pulley bearings later I have a nice zero turn. A little maintenance as with any machinery, it's been a dependable tool.
Yeah, it has it's place in the scheme of things right next to the Groundsmaster.

I hate grass.

 

[YardBikeBob]

For me Bob I found I saved quite a lot of time by using a dedicated mower as opposed to a mowing deck on the tractor. Some years ago (15? 20?) I got a reasonable deal on a Groundsmaster and never regretted the decision, over all it easily cut my time spent mowing by more than half what it used to take.

Huh. Everyone says that: Mowing behind a tractor is slow. Several friends in the KC area swear their ZTRs are just the ticket for their gentlemen ranches. A good friend paid just about as much for a really nice Grasshopper as my tractor. His lawn is also beautiful and groomed.

But I have just some old, bumpy fields I'm trying to spiff up. I am curious how fast ZTRs can deal with uneven ground. And rocks. I can drag the mower at a good clip across this old pasture right up until my suspension seat goes to full compression and my beverage froths over.

My 6' cutter will have to do for a couple of old people to enjoy the view during happy hour and a little toil in the garden.

You might have a respectable name.

RDAllen

 

[orangeandgreen]

I have an older Woods 10 foot cutter that has extremely slow tip speed, when doing the yearly CRP trimming, it pushes some grass over instead of cutting it if the blades aren't sharpened. The fields look good right after they are cut then the grass starts standing up after a couple days. I found it does much better with a yearly sharpening. Before owning this cutter, I had never heard of shapening a "bush hog"
A neighbor has a similar cutter that is a couple years newer and leaves a much nicer looking cut. I looked up the specs and he has different gearing (faster) in the outboard gear boxes. For $1400 I could put the "new" gear boxes on my cutter, or just sharpen mine every year..

 

[k0ua]

Every time I think about sharpening the blades on the Bush Hog, I hit another patch of rocks, and think "nah". I don't have any grass to mow with it anyway, just brush, and weeds. (and rocks:laughing

When I lived near Willard, I had lots of grass, and had a nice rear finish mower.. I sharpened its blades often.

 

[rsallen]

Huh. Everyone says that: Mowing behind a tractor is slow. Several friends in the KC area swear their ZTRs are just the ticket for their gentlemen ranches. A good friend paid just about as much for a really nice Grasshopper as my tractor. His lawn is also beautiful and groomed.

But I have just some old, bumpy fields I'm trying to spiff up. I am curious how fast ZTRs can deal with uneven ground. And rocks. I can drag the mower at a good clip across this old pasture right up until my suspension seat goes to full compression and my beverage froths over.

My 6' cutter will have to do for a couple of old people to enjoy the view during happy hour and a little toil in the garden.

You might have a respectable name.

RDAllen

Nah, not suggesting do anything you don't think you want to do. Just giving the arc of how I (and perhaps others) come to have more equipment than I would have ever expected when starting the reclamation effort. As to how the Groundsmaster handles the roughness of the ride ( and nope I didn't pay a lot for it), the good thing is it moves as fast or slow as I need it to. Which of course also makes things go faster overall. lol, and if my beverage of choice starts foaming over......I drink faster.

Any ways, this is just another chance to say how much I hate grass. lol

I hate, I absolutely detest grass.