What size grinder for sharpening brush hog blades?

[jkwilson]

Time to mow the pastures, and I got started sharpening blades last night. My old auction-bought $12 7" grinder seems to have a drive issue and the spindle is locking up on me. I need something different to get the job done.

It's a 3 spindle mower, so I have to do 6 blades every few years. It's a job, but I don't do it very often. The blades are about all I use the 7" grinder for. I have several 4 and 4.5" grinders for lighter work.

I was going to need some new wheels as I only have 2 more, so that really isn't a consideration.

What size would you go with, 7" or 9"? I'm leaning to the 9" because my brain says the 7" is so much faster than the 4.5" that the 9" must be even better. But is it?

And after that, what would you buy? Looks like several in the $200 range, several in the $130 range, and then the Harbor Freight in the $65 range. My gut tells me that even though a new Makita or Milwaukee would be a nice tool, my needs will be met by the HF and I save money.

Thoughts?

 

[Bobcat753]

Personally I'd look at the hitachi or a dewalt 7". The bigger you go the heavier it gets. For new wheels I'd look at metabo or 3m cubitron.

 

[gungatim]

I use a 4". HF brand angle grinder. way too hard trying to sharpen blades on a bench grinder. Just stick them in a vice and go at it.

 

[jkwilson]

I use a 4". HF brand angle grinder. way too hard trying to sharpen blades on a bench grinder. Just stick them in a vice and go at it.

The difference in a 7" and 4" grinder is night and day on these big half inch thick chunks of steel. I wouldn't even consider using a bench grinder on them.

 

[sberry]

Neither. Go to Walmart and get a 4 1/2, 30$ and is about as good as any grinder they make. We sharpen in place.

 

[8man]

Agree with Sberry, in place if you can support it where you can get to it with an angle grinder. Safety first.

 

[GCncsuHD]

I always just lift up the bush hog, set it down on jack stands, crawl under and go to town with an old Craftsman 7" that's about twice as old as me.

 

[oldldh]

A "Real Man"---


Would just use...


A Flat *******...File...


Take him about 5 minutes per blade!!!


(I'd use a big Reed/Starrett/etc vise to hold the blades and a BIG Angle grinder...)

 

[sberry]

I am using one now and did this the other day. Yes, a couple jackstands and a piece of cardboard to sit on. a big C clamp or I can clamp an 11R on it to hang on to really helps and sharpen often.

A full powered 4 1/2 grinder will tire a man out in a hurry out of position. A big heavy more powerful monster to remove and detail a small amount of material isn't going to help. I used part of one wheel on my 7 inch air in the last 20 yrs, my nine broke 30 ago and never replaced it. I overloaded some units along the way in a hurry, you wont do it here. It was operator error.
Don't fuss over wheel quality, there aint night and day difference. Look for a good supply priced right. I am not a big fan of cut offs for electric, they are good problem solvers, I hate the mess and the noise and like variable speed but for general fab work a 4 1/2 x 1/4 is the standard, some apes use a size bigger but you aint a pipeliner etc.

 

[sberry]

I always just lift up the bush hog, set it down on jack stands, crawl under and go to town with an old Craftsman 7" that's about twice as old as me.

Right, its a tool you already own and are familiar with. If the op doesn't own a grinder that will do this job a small one is the starting point. I am a career welder and could use any method made, any size, any wheel, I use the same one I do for everything else.

 

[PT Doc]

2x72 belt grinder

 

[dr_clyde]

I really like my 6" metabo. It has 12 amps and can handle a 6" wheel, but I usually fit it with a 5 inch 36 grit disc for general grinding tasks. It has a lot more torque than a standard 4 1/2" grinder, and isn't much bigger.

If you're looking for an excuse to buy a new tool, go for it. I love my big 7" metabo as well. If you need to just get the job done and already have a 4 1/2" grinder, just put an aggressive ceramic fiber disc on it. Should make short work of brush hog blades.

You'll find that a standard grinding stone isn't as efficient as a nice ceramic disc. Even an underpowered tool can really move some metal with a coarse one of those attached.

 

[GCncsuHD]

Right, its a tool you already own and are familiar with. If the op doesn't own a grinder that will do this job a small one is the starting point. I am a career welder and could use any method made, any size, any wheel, I use the same one I do for everything else.

He did mention in the first post he has several 4.5"s, and had been using a 7" for this job until it died. It appeared he was asking if a 9" would be even better for the job.



If you keep up with it and touch it up several times through the season a 4.5" will do the job great, but if you're like me and slack off on that, not to mention have several spots with boulders sticking out of the ground in the fields, it takes a 7" to fix those "oops" marks.

 

[SARG]

I have a small brush cutter with two blades. I sharpen them with a 4 ½ inch grinder while on the cutter. Touch them up every other time I use it.

 

[sberry]

Yes, easy to miss some details, all these threads run together,,, ha. Ok,,, if my 7 died wouldnt bother replacing it to zing a couple blades on occasion especially if I had a decent 4 1/2 handy.

 

[sberry]

I am with the dr above, certainly not against buying something to improve things but there is no reason not to get on with your day. I went in a shop he other day and the boss was gone, 2 guys dicking off, one sitting round watching a blade sharpen. It paid for the man the tool and them some. I wish I was in the spot to spend some on tools and see a return, I hit a spot where ambition is the biggest asset or input.

 

[justme-]

FWIW we sharpen blades every day (part of service) and use an 8x36 chisel grinder (think bench belt sander on steroids) with a 36 grit belt free hand under the bottom roller. Takes about 2 blades to practise and get the hang of it. That said, if you know what you're doing the tools is far less important than the knowledge. I doubt a 9" would be any better than a 7, tho I can see how a 7 is better than a 4-1/2. I would suggest dropping grit to a 36-40 range if you can find it in whatever you use and you may find it is faster than a normal box store disc, which are usually 60-80 grit.

Also since it should be understood but has not been said, make sure to balance the blades after sharpening, and if you hit "boulders" even with a brush mower, check for a bent blade before spending the time sharpening.

you also may consider looking for double edged blades, or making yours into them. One of our rental brush mowers has that so a quick flip gives a sharp edge again - tho 90% of the time we have to replace the blade from meeting those boulders and fence rods before they get dull enough to flip.

 

[kenburkholz]

A few years ago my kids bought me a H.F. 9" angle grinder for my birthday.I have never seen anything with that much power. I don't use it for everything because it's just too heavy! The combination of weight and power will blow you away,you need to watch how fast you remove material. Ken.

 

[kenburkholz]

When I worked for a pipeline outfit years ago,there were several places on the right of way we couldn't use herbicides, so we had to use tractors with field mowers. The blades don't last long with rocks and stuff. So , we made our own flails with a mounting flange, a length of heavy chain,[ at least 1/2"thickness] . These worked well for us, but use these with extreme caution. Ken.

 

[Mohawk Dave]

People still use bench grinders with grinding wheels?

4.5" Metabo, or Makita/Milwaukee/DeWalt with a flap disc. 100x more control and precision. And f-ck HF 4.5"....vibrate your hand off.

 

[sberry]

I could just about get by without a bench grinder. I use one on occasion for wire wheel and an occasional drill bit and even that I can do with a hand held.

 

[bobcatdan]

Unless your blades are as dull as flat stock, a 4 1/2" will clean up brush hog blades just fine.

 

[sberry]

Wouldn't take but a wheel if they were.

 

[jkwilson]

I appreciate everyone's input on this. I'm still not sure what I want to do. I think before I go any further I'm going to try a blade with a coarse wheel on one of my smaller grinders just to refresh my memory on what it's like. In my mind, the 7" was much better than the smaller ones, but others chiming in that the small ones are good makes me wonder if I was really comparing apples to apples when I tried it many years ago.

Maybe I was using a coarser wheel on the 7" than I was on the small one and thought the size was the difference and it turns out it was the wheel. Wouldn't be the first time I thought I was smart and turned out to be dumb.

 

[juicedapple463]

People still use bench grinders with grinding wheels?

4.5" Metabo, or Makita/Milwaukee/DeWalt with a flap disc. 100x more control and precision. And f-ck HF 4.5"....vibrate your hand off.

No sh-t, I was helping my father grind some stripped nuts and he has a 4.5" HF grinder and holy sh-t my hands felt like they were going to fall off from the vibration.

 

[sberry]

The super cheap HF are not very good and a waste of money. They don't work right. But they do make a fairly good grinder at about the 30$ level that after it hit the gang box for a while wouldn't be able to tell from any other. You cant buy one for 9.99 and the Cheapest good grinder they make can be had occasionally at Menards on sale for 20. They must clear them at cost.

 

[sberry]

You want a common 1/4 steel grinding wheel.
I used to stock a box behind it, I still panic a bit if I look over and see it low. I bought 20 and tossed a couple on the trucks. Its the type of stock I never want to have to stop to get. Gasses the same way, if something comes up want to be able to work a week or 2 without nickel and diming.

 

[sberry]

The only reason I don't use flap disks is that I have air and use a sander although I might try one on a spare grinder for a couple jobs. I can finish quite fine with a common wheel though. I am a pretty fair welder but I am a super grinder.

 

[catalytic]

If you use an angle grinder on your heat treated blades, you will ruin the temper

It is extremely difficult to grind blades with a grinder and not heat them up enough to anneal them or destroy the temper (so you end up with soft blades that appear sharp but don't hold an edge).

This is what belt grinders are for -- the belts carry the heat away so the metal gets barely warm to the touch. Basically, the three price points are harbor freight 1x30 belt grinders (usually $35 on sale), grizzly 2x72, or Burr King 1.5 x 60 (or 2 x 60 or 2 x 72) (around $2400 shipped -- mower blade sharpening guides available). Youtube "Burr King 760 mower blades" for a ton of videos.

 

[Mohawk Dave]

If you use an angle grinder on your heat treated blades, you will ruin the temper

It is extremely difficult to grind blades with a grinder and not heat them up enough to anneal them or destroy the temper (so you end up with soft blades that appear sharp but don't hold an edge).

This is what belt grinders are for -- the belts carry the heat away so the metal gets barely warm to the touch. Basically, the three price points are harbor freight 1x30 belt grinders (usually $35 on sale), grizzly 2x72, or Burr King 1.5 x 60 (or 2 x 60 or 2 x 72) (around $2400 shipped -- mower blade sharpening guides available). Youtube "Burr King 760 mower blades" for a ton of videos.

I agree with heating up too much...but give me a flap disc on a 4.5" and I'll keep that sucker cool with fast light-medium passes. I don't overheat my stuff...

 

[catalytic]

I agree with heating up too much...but give me a flap disc on a 4.5" and I'll keep that sucker cool with fast light-medium passes. I don't overheat my stuff...

confession: I've done this too. However, you have to be SUPER careful -- even if most of the steel feels cool to the touch, the very thin edge heats up much faster than the rest, and it's really easy to draw the temper away to 1/16" back from the edge (where you need it most). There's also a problem because flap discs are rough grit, so you never really get things properly sharp. With a belt grinder, you can go up to 2000 grit if you have the patience (I wouldn't bother for the Brush Hog, but I also wouldn't stop after rough flap disc grit).

There's really no reason not to pay the $35 and grab a belt grinder from horror freight. Or if you don't want to remove the blades from the machine, then a pneumatic or electric handheld belt grinder (the type for grinding welds) is the thing to have (like this: http://www.nationaltoolwarehouse.co...eYt_m4j2mOeNfz5H5e5dzDzJBjBhxtaAWIRoCmK3w_wcB
)

As with any power sharpening work, keep touching the steel to make sure it's only warm to the touch no matter what you use.

Or if you don't want an excuse to buy more tools, then grab a medium coarseness USA-Nicholsen or Century ******* mill file. This will sharpen them up really fast -- a few careful passes to expose new steel is all that is needed unless you've been brush-hogging rocks.

 

[Mohawk Dave]

Yep. What catalytic said. I keep a utility grind on my lawn tractor because it eats twigs, small branches, and the random dog toy. Using a file after a flap disc is great. And flap disc come in finer grits. Or do what I do and keep a worn down flap disc on a grinder. Its what I also use to finish off the wedge and burn the top of the shaft when I head a hand tool.

 

[Rookie2]

I would take the blades off and chuck em up in my friends milling machine ! Im too old to be climbing under a death trap mower I borrow once a year.

 

[MagnumForce]

I would ditch the 7 inch and go with a 4.5 inch Metabo with flappy disks as well, so much better!

I have never found anything better for heavy industrial use, my Metabo runs for hours every single day, 5 days a week for the last 5 years and only issue I had was replacing the 69 cent switch lock. We have Milwaukees and Dewalts and they don't hold a candle to the Metabos. In fact if it is an angle grinder, we call it a Metabo at work no matter the brand.

I never use our 7 inch Metabo as you just don't have the control. The 4.5 inch with flappy pads will make very quick work of the job with awesome control and a perfect edge.

If you are dead set on a 7 inch, I would still go Metabo.

 

[gearhead1]

My bush hog was so old, I couldn't get the blades off without cutting the pivot bolts with a torch. I lifted up the mower on the tractor, used a jack stand to hold the deck, and crawled underneath to sharpen blades with a 4.5" grinder. I wouldn't have had room for anything bigger. It worked fine.

 

[PT Doc]

Ceramic will cut nice and cool and get the job done with careful attention to the pressure used.

 

[Packard V8]

If you use an angle grinder on your heat treated blades, you will ruin the temper

Like most absolute statements, the above is absolutely not true in all cases. Some of us have been sharpening many blades with an angle grinder for many years without ever ruining one.

Conversely, I've seen blades ruined on a belt grinder because the operator didn't know how.

BTW, its the first inch of the blade which does the cutting. As long as that's sharp, the rest matters little. If the blade has an angled outer end, sharpening it shortens the blade. On two-blade decks, if the blades get too short, it will show up as uncut blades of grass left down the middle.

jack vines

 

[justme-]

Guys, unless you're heating the blades enough to blue the steel you're not affecting the temper at all and even blueing them only occurs at the thinnest edge until you get so overboard it's ridiculous. You're working on a lawnmower blade not a straight razor, or a scalpel. If you're grinding that hard and long on that chunk of steel you probably should replace the blade instead of sharpening it.
As long as you're not heating it to change the color of the steel (400*f I believe) you're fine. This is a common question that comes up on knife/razor restoration forums.