How and when to sharpen Rotary BH blades

[hz293]

I have a bush hog that I bought a short time ago. My land is mostly 15 degree or better slopes and the terrain is quite uneven. To be safe, I mow up and down the slopes. Actually because of some of the terrain I can't always tell if it's up or sideway because it's deceptive I find that a lot of time I'm englfed in dust. Even if I raise it, if I want to cut weeds and tall grass the brush hog will bottom out and hit dirt. There's a few small rocks but not a bunch.

My question is, how do you know when it's time to sharpen the blades and how do you do it. I looked at the blades when I got it and it just looked like flat stock. what am I missing?

Harris

 

[Bird]

If you use the search function, you should find lots of previous discussions on the topic of sharpening brush hog or rotary cutter blades. Most manuals say to leave approximately a 1/8" flat edge on them instead of making them sharp as you would with a lawn mower or finish mower. That's because they are made to cut (or shatter) woody type material (brush, bushes, or saplings) and a razor edge would very quickly have nicks in it. Of course if all you're cutting with yours is grass, you can certainly sharpen it to a finer edge to get a neater, cleaner cut.

As for how to sharpen it? Some sharpen the blades with an angle grinder without removing the blades from the machine. Others remove the blades and sharpen them on a bench grinder or put them in a vise and sharpen them with an angle grinder. I've tried all three of those methods and don't know that I have a preference, but of course, I had an air impact wrench to remove blades. If you don't have big enough or strong enough wrenches to remove the blades, then the angle grinder is the way to go.

 

[Theowegian]

Hoist that puppy way up in the air and get your angle grinder out and grind away. It's the simplest and fastest way.
If you try and take the blades off, you'll get frustrated VERY quickly....

 

[Farmwithjunk]

I have a bush hog that I bought a short time ago. My land is mostly 15 degree or better slopes and the terrain is quite uneven. To be safe, I mow up and down the slopes. Actually because of some of the terrain I can't always tell if it's up or sideway because it's deceptive I find that a lot of time I'm englfed in dust. Even if I raise it, if I want to cut weeds and tall grass the brush hog will bottom out and hit dirt. There's a few small rocks but not a bunch.

My question is, how do you know when it's time to sharpen the blades and how do you do it. I looked at the blades when I got it and it just looked like flat stock. what am I missing?

Harris

When? When they need it. Actually, it's best to touch them up periodically BEFORE they really HAVE to be ground. It's easier that way and you don't have to suffer through poor results mowing until the baldes are too far gone.

I usually sharpen 3 or 4 times a summer. That translates to around 15 to 20 hours of mowing between touch-ups.

How? In 35+ years, I've removed ONE set of blades to grind. It's unneccisary and time consuming. I raise the mower as far as the 3-point will lift it, then back the tail wheel up onto my trailerto support it. I block the front end with jack stands or wood blocks. Even then, I don't actually get UNDER the mower. I don't want to be a statistic.

4" angle grinder and a face shield. Don't grind the edge at too abrupt of an angle nor too flat. 55% seems to work well for me, although I usually just "eyeball" the angle. Any nicks or rolled edge that sticks below the cutting edge, I grind off flat before working the cutting angle. Then I grind just enough to clean up the edge. They don't need to be like a surgical scalpel. Slightly blunt edge does a sufficient job. Too sharp cuts brush rather than shattering it. That leaves tire killers. Too sharp also doesn't hold an edge for long in dirt,rocks, brush and all the other assorted gremlins a bush hog gets into. I try for 1/16th" at the absolute sharpest, and prefer around 1/8th" blunt edge.

 

[radman1]

I may be alone on this one, but I have never sharpened bush hog type mower blades. I figure they are for a rough cut and I usually hit rocks, limbs and so on. My 6' mower is probably 20 years old. Heck, I never look under the thing unless something wrapped around the blades. Maybe that is where Jimmy Hoffa is? I bought is used 10 years ago for $250 but have changed the gear box oil and grease it regularly. Just mowed down probably 100 cedar trees, some 5'-6' tall two weeks ago but went very slow over the big ones.
Finish mower blades are a totally different story. 3-4 times per year.

 

[hsvhobbit]

Factory recommends my blades get sharpened to 1/16" at the edge (Rhino SE6) I check them every few hours and only felt I had to sharpen once (after maybe 20 hrs of cutting). I raise the rig up, put concrete blocks under the edges so I don't get surprised and use a 4" angle grinder, takes about 20 sec of touch up per blade and it's done.

Total time from when I shut off the tractor to when I turn it back on again is around 5 min or so.

 

[have_blue]

I may be alone on this one, but I have never sharpened bush hog type mower blades. I figure they are for a rough cut and I usually hit rocks, limbs and so on. 3-4 times per year.

Agreed! A brush hog used as intended doesn't benefit much from sharpening at all. Heavy brush, rocks, and dirt piles will only undo a sharp edge in 30 minutes.

Problem is, when you hog your rough stuff and remove your rocks, you end up with a nice grass field. Instead of buying a finishing mower, I kept using my brush hog, trying to make it mow like a finishing mower. In my case, it helps a lot to keep the blades sharp. It's like daylight and dark. Sharp blades do a 200% better job, and require a lot less power. I keep my blades dead sharp, and do a 15 minute touchup before each use. Reducing the PTO RPM just a bit keeps the blades sharp 2x longer.

 

[wetrombley]

I have a similar situation with my 6 ft. bush hog blades. Over the past two years I've noticed that they just are not cutting as cleanly as I would like. I would like to sharpen the blades in place and wondered how difficult it would be with an angle grinder. Since my tractor is a Mahindra 3510, I want to get all the cutting action I can without sapping the horsepower.

 

[J_J]

I have a similar situation with my 6 ft. bush hog blades. Over the past two years I've noticed that they just are not cutting as cleanly as I would like. I would like to sharpen the blades in place and wondered how difficult it would be with an angle grinder. Since my tractor is a Mahindra 3510, I want to get all the cutting action I can without sapping the horsepower.

It is not difficult at all. Just raise it up, support it, and go to work on the blades. They don't need to be real sharp. Don't even crawl under there, just reach in with the grinder.

If you have the stuff to remove the blades, do so, and sharpen. Impact wrench, 1 1/2 socket, or whatever. There is a hole in the top plate with a cover. just for this.

 

[greenmule]

Got a 5 ft kk cutter that has 7-8 years on it just cutting grass and weeds,very little brush,no rocks,etc. Still does a fine job cutting, never sharpened blades.

Figured,[if mower still is workin when they do need some attention] would just take torch,cut bolts off,and put new blades on,seems the simplist thing to me to do.

Always sharpen my own lawn mower blades[got an old sears mower that I have shapened probably 10 times,same blades] so not worried about doing it,just figured to sharpen them right,would need to take them off hog,and if I was going to go through that probably painfull procedure,would just cut bolts off and put new blades on,than I'd be good for another 10 year??!!

 

[cisco]

Lots of prior posts on this issue, like most others. In brief, rough cutting requires little in the way of blade sharpening unless one has really rocky soil, lots of raised stumps or similar. For finer cutting, grinding out major nicks in the blade edge, and narrowing such to the 1/8 - 1/16 inch range, is preferable (examine the cut end of the grass before and after you sharpen the blade, and note the ease with which your tractor/hog combination runs). I change blades every few years, for a large field grass area my wife likes to see "nice", keeping the last used set for rougher stuff, like thick brush, saplings and such. I sharpen the blades every month in about 15 minutes - time to raise cutter as high as 3pt will allow, place blocks under the cutter, put on a faceshield and use an angle grinder. Every 6 months or so I drop the blades off with a 3/4" impact wrench (my 1/2 inch was not up to the task - it's a 1 & 13/16 nut), and use the bench grinder. .......And if all I did was cut thick brush, and my wife wasn't looking over shoulder, I might pay a lot less attention to the blades. That said, putting a bit of an edge on a rotary cutter blade is EASY.

 

[sld]

If you are going to go to the trouble of sharpening them I would take them off and do it right.

You really should attempt to balance them, even if it is just hanging them on a nail. I can tell when mine are slightly out of balance but maybe that is just because I have a smaller tractor.

I like to feel the smoothness in a beast like a bush hog.

 

[PM1]

I've never tried sharpening my blades with an angle grinder while still mounted, but it sounds easier than removing and reinstalling blades. The bottom edge of the blade is flat, and the top edge is beveled. How do you grind the top beveled edge (and see what you're doing) with the blades still mounted?

 

[skipmarcy]

I've never tried sharpening my blades with an angle grinder while still mounted, but it sounds easier than removing and reinstalling blades. The bottom edge of the blade is flat, and the top edge is beveled. How do you grind the top beveled edge (and see what you're doing) with the blades still mounted?

It's the way I've always done it - it's ridiculous to R&R blades for a sharpening. As far as balancing them - I've been sharpening the set on mine now 3 or 4 times a year for about 8 years and have never had a balance problem. Touching-up the edge with an angle grinder might take 1/4 oz. to 1/2 oz. of metal off - not much affect on a blade that weighs about 10 or 15 lbs. I just bring the 3 point up as high as it will go and shorten the toplink and the rear of my cutter is right at eye level while sitting on a small crate. I clamp a pair of vise-grips to the end of the blade I'm working on and let it butt up against the cutter housing to hold it still. Plenty of room between the deck and blade for my 4 1/2" grinder. I guess if you have a rear guard of some sort you would have to remove it but mine doesn't have anything. I can touch my blades up in less than 5 minutes and get a nice cut on my yard.

 

[LoneCowboy]

It's a rotary cutter, not a finish mower.
If you want a perfect cut, get a finish mower.

rotary cutters (aka bush hogs) don't cut, they shred. (I like that in Texas they call them shredders, it's a much better name). Look at the tip of the grass blade that gets cut, it's literally torn apart, not sliced clean like a mower. Sharpening doesn't do boo.

90% or more of the cutting happens on the far tip of the blade. When that tip gets worn back an inch or so at a 45 degree angle, you aren't hitting the grass/weeds with a straight edge and the grass slides off instead of being hit at 90 degrees. When that happens, it's time to replace the blade because it won't cut well, it's just bends it over.

There is no sharpening. The cutting isn't happening at the "edge", it's happening at the far tip of the blade, where it's spinning the fastest.

When that tip wears down, buy a new blade and replace.
For us it's every 500 to a 1000 acres.

 

[J_J]

The reason that people sharpened bush hog blades, is that they do want a better cut. When you get a new bush hog and cut a field with out a lot of debris, it does a very good job, and as the blades wear from use, it does start to tear and shred the grass. You could even use a flat faced blade, and it would cut better than a rounded off blade. Some people say they never sharpen, but to each his own. You won't get into balance problems unless you grind more off one blade than the other. Most of the blades start off with a slight edge to them. You all should know by now that a sharp blade cuts better, in any situation. When to sharpen, is your choice. I have even thought of welding some hard surface on the first 2 in of the blade, to reduce wear. It should work.

 

[Deadman]

Its so much easier to just take the blades off, and clamp them in a vice.

 

[J_J]

Its so much easier to just take the blades off, and clamp them in a vice.

What you say is true, but a lot of people do not have air, or a big enough socket, or the torque necessary to take off the bolts.

 

[jb62901]

Took my blades off the other day and did a touch up on them. Weighed them, one at 8.000 and the other at 8.005 think Im good to go this time around. Used a floor jack to reinstall, worked like a champ.

 

[pitt_md]

The reason that people sharpened bush hog blades, is that they do want a better cut. When you get a new bush hog and cut a field with out a lot of debris, it does a very good job, and as the blades wear from use, it does start to tear and shred the grass. You could even use a flat faced blade, and it would cut better than a rounded off blade. Some people say they never sharpen, but to each his own. You won't get into balance problems unless you grind more off one blade than the other. Most of the blades start off with a slight edge to them. You all should know by now that a sharp blade cuts better, in any situation. When to sharpen, is your choice. I have even thought of welding some hard surface on the first 2 in of the blade, to reduce wear. It should work.

I agree with the above. I don't know that it makes a difference when wading through thick brush but I can tell you it makes a lot better cut on tall grass/clover when sharp. It still is not a "finish" quality cut but its pretty darn good.
If it didn't matter if the blades are sharp or not why do the new ones come with a sharp edge?