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How do ya ll get at your large MMM blades 4 sharpening

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gball7
Join Date: Dec 2007
Posts: 43 North Carolina
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2008-03-26          152437

All,

I just bought a new Kubota BX2350 with 60" MidMountMower. I have a front end loader, so I could use it, once I've removed the deck from the tractor, to hoist the deck so that I can get the blades off and then use the bench-grinder to sharpen them.

But how do you guys go about sharpening your blades? Is this the only way to do it, or do any of you use other methods?

Thanks in advance,
Mike


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Murf
Join Date: Dec 1999
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2008-03-26          152443

We sharpen more blades than I care to think about in a year.

All are done the same way. Blade is clamped in a bench vice, and touched up with a 4.5" hand-held angle grinder. A very simple balance beam scale is then used to ensure they are equally ground and still balanced.

A couple of tips though, never grind them to anything but a 45° angle, and never sharpen them to a knife edge, always leave a little flat spot on the face edge, about 1/32" - 1/16" in thickness depending on how stout the blade is, finish cut or bush hog type.

If the blades are in tough shape, replace them, they're not expensive, and compared to the cost of the damage an out of balance one will do it's cheap insurance.

Best of luck. ....

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auerbach
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2008-03-26          152447

Also, don't let the grinder heat the blade, by keeping it moving and not pressing too hard. If they really need sharpening, take them to a pro. Doesn't cost much. When you see how they look when properly done, you can aim for that yourself next time. ....

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bvance
Join Date: Jul 2004
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2008-03-26          152460

Murf,

Just curious, why should one leave a 1/32 blunt edge?

Brian

....

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bvance
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2008-03-26          152461

GBall,

You asked how one gets at their blades to remove them and you indicated you hoist the deck with your FEL.

I just flip mine over on the shop floor and remove the blades that way. I can do it by myself and I would guess you only have to lift 80 pounds or so as most of the weight still rests on the floor.

It would seem that removing the blades while under a swinging and suspended deck would be a bit awkward if not dangerous. I also find that you have to wedge a block of wood between the blade and the deck frame to keep it from moving for easier wrench torque.

Brian ....

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kwschumm
Join Date: Feb 2003
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2008-03-26          152462

Bvance, my guess is that the blunt edge is less prone to be a source for dings that might start stress cracks. I'm curious what Murf says. ....

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gball7
Join Date: Dec 2007
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2008-03-27          152471

Great points guys.
Bvance, I was thinking of a similar scenario to what you do (flipping the deck over on the shop floor), only using the FEL, while backing the tractor up, to slowly flip the deck upside down. I agree being under a hanging deck, much less only supported by hydraulics that can leak-out/lose pressure, isn't very safe. I suppose though if I just lift under the front edge, as it sounds like you do, that a 250 lb. deck could be flippable without using the FEL. I might need to buy a new center blade as was suggested, as the middle one and the rock both suffered pretty badly when they met. The barbs/malformations on the center blade's leading edges are about 1/4" high and are peppered in several places along the edges. I still feel that all three blades need a touchup the way they came from the factory--- fairly blunt on the edges, but as suggested, I guess it's good to have a blunt leading edge. I'm only running engine @ 2400rpm while mowing during the run-in period (pre-50 hrs.), so I think sharper blades would definitely give me the best cut. Right now I'm missing some grassblades now and then. I think if I were at full tip speed (e.g. 3000rpm) this wouldn't be an issue.
Mike
....

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Murf
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2008-03-27          152474

The blunt edge on the blades is not as important for a finishing mower that is unlikely (supposedly) to hit anything it is not as critical as in the case of say a bush hog type mower, or a commercial cutter that is constantly working, and on different and often unknown sites.

The logic is that no matter what you are cutting, or where, the blades will dull and hit things, even if only the odd piece of stone or gravel that ends up in the grass. If the blade is honed to a sharp edge it creates two problems.

First, it doesn't subject the lead edge to as much heat which takes the temper out of the steel, but even if the blade is ground to a sharp edge without subjecting it to much heat, as with a water-cooled slow moving stone, the thin edge will never stand up to the stresses of doing it's job. The inevitable result is that the lead edge either gets worn away, or chips and breaks off, leaving a blunt edge very quickly. That blunt edge negates any benefit you just got from the sharpening.

Secondly, and most importantly, if you start with a rather blunt edge, the lead edge will last a lot longer, and the longer you can keep the edge as close to the way it's supposed to be, the better. Better performance, better cut, better all around.

It's a difficult concept to get your head around, but even a big nasty blade takes a heck of a beating just cutting grass. Bear in mind, those blades are really moving along. As an example, if we use a 5' bush hog, running at 540 rpm, the blades are spinning at 1.6 times that speed, so they are turning at about 864 rpm, if the blades are 5' in total, they are turning in a circle about 15.71' around the perimeter. That means each blade tip is going to turn at (864rpm x 15.71") a rate of 13,573 feet per MINUTE. That is 154.8 miles per hour!!

At that speed nearly anything will wear out steel.

Best of luck. ....

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gball7
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2008-03-27          152476

Wow- awesome primer, Murf. So I guess the somewhat blunt edge I felt when feeling under the deck when the tractor was delivered is about right all told. Perhaps I should just buy a new center blade... and keep the even bluntness on all three (replace the messed up center blade).

Anyone have an idea what a new blade for a Kubota BX60MMM deck might cost? I'll probably be calling the dealer soon to find out. ....

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Murf
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2008-03-27          152477

No problem, happy to help.

Dealer, I don't know about pricing, but after market blades usually cost less than the gas to go get them.

If you are looking at replacing the blades, I would highly recommend you go with a high lift mulching blade like the Gator brand units.

They will give you a nicer (IMHO) cut and the difference in performance is unbelievable. The high lift makes the blades of grass stand up to be cut more uniformly, and will re-cut any dry clippings or leaves.

They virtually eliminate any visible clippings if you cut regularly and don't let it get too long.

Best of luck.

....

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gball7
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2008-03-27          152501

Good info again, Murf. I emailed my dealer today and he said a single blade for my Kubota 60"MMM costs roughly $16.00... so yeah, I think I could have him UPS it to me for less than the cost of fuel to go pick it up myself (the dealer's over an hour an a half away one-way from my property). May look into the special blades you mention also. ....

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bvance
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2008-03-27          152502

Murf,

Thanks for all the great info on the blunt edge etc. I knew you would have a reason and thanks for sharing it!

Where might I find the Gator blades?

Brian ....

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bvance
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2008-03-27          152503

Mike,

Just another suggestion on using your FEL to flip your deck.

If you do as you suggest you might, you would need something to block the deck as you were backing up otherwise it would it would just keep sliding towards you. Additionally, just as you get the deck to tip over the center of gravity, you will have some slack in the chain from about 1 foot before COG and 1 foot after, which will cause the deck to free fall somewhat before the chain catches it. And as it falls several inches or so, the far edge of the deck still on the floor will likely kick out a bit which may cause some minor scratches or damage. Not to mention potential stress points of where the chain must attach to. I'm not sure I would try that. At the very least, you would get a lot of jerking on the chain and the attached stress points.

As I said, I just flip mine myself. I get it to COG and carefully walk around it while I keep it at COG and then let it down again. Someone could help you and make it even easier. Your wife could easily hold it at COG while you walk around to the other side.

Brian ....

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kthompson
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2008-03-28          152507

Does a MMM not have a oil filled gearbox? If so flipping it would seem not to be a good idea (assuming it has a vent). Lifting your deck and then blocking it with solid wooden blocks it a safe method. A floor jack is a good tool for such and is what I find works best on my ZTR for this. (Tried to remember why I gave away my ramps first time to remove blades from ZTR.)

Impact wrench helps with problem of trying to hold blades while removing or tightening them.

Mike, you may find a closer place to buy your blades if you have the old one in hand. If you are near an Agri Supply (NC is their home) they stock many blades made by Oregon at a good price. They are on line and will ship. They stand behind their product very well. kt ....

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Murf
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2008-03-28          152510

Either Google 'gator blades' or any place that sells and services commercial turf equipment will have them.

Best of luck. ....

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bvance
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2008-03-28          152525

KT,

It does have an oil gearbox but I have never had any trouble with it leaking. Blocking it up means you have to crawl under and that's a big hassle. It's just easier to flip it, take off the blades, sharpen and then put them back on. It really isn't a problem at all.

Brian ....

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gball7
Join Date: Dec 2007
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2008-03-29          152540

Good dialogues, guys. I do think the gearbox is oiled, and the info on relatively lightweight at COG is good. If flipping the deck, I just don't want it to pass 'no return' and crash down, which sounds like it's avoided by this method. I suppose (as alluded to) driving the front end up on ramps would also work- as long as parking brake is all on and the wheels are chocked off. I will check on Agri Supply. My Kubota dealer did say they could ship a single blade to me. Have a good weekend everybody.
Mike ....

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bvance
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2008-03-29          152543

Mike,

If you are concerned about the weight, when you do it the first time have a buddy help you and try it the first time with both of you and the second time with him just assisting slightly. If you are comfortable doing it by yourself, there's your solution, if not, you could try a couple of the other solutions suggested here.

Brian ....

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DennisCTB
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2008-03-29          152545

I got these mower stand axles and wheels from Larry's Moweraxles. I put them on at the end of the season.

I lift the deck by myself, it is not that bad, two people and it is a piece of cake. I used to do it befre I had the moweraxles as well and just placed some moving pads behind it when I laid it on its back.

I like the space saving of the moweraxles so its worth it to buy them and go through the extra work to install them.

....


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DennisCTB
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2008-03-29          152547

I have been using a big grinding wheel on my blades and it is hard as hell to get a nice consistant edge. This angle grinder idea sounds good. Is a $30 buck Black and Decker 4.5 inch angle grinder up to the task or do I need to spend more for something I will only use on the mower blades? ....

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gball7
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2008-03-29          152549

Dennis,
Those Moweraxles are pretty cool. Seems like those would do the job.
All, what's the difference between putting the blade in a bench vise and using an angle grinder, vs. holding the blade and using a benchgrinder? Any preferences? Sounds like more of you use the angle grinding?
Mike in NC (this weekend rainy & cool NC) ....

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DennisCTB
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2008-03-29          152550

Over the years I have used:

1)hand file
2)cheapo Bench Grinding wheel
3)Belt Sander
4)Heavy Duty Bench Grinding Wheel

I would have to say that I got the best job from the hand file. I may just be using the Bench Grinder wrong but grinding a smooth edge against a wheel is tough. I went and bought a bigger bench grinder because the toy one was so slow and the grinding so imprecise.

I was hoping that since an angle grinder places the grinding disk flat against the blade that getting a straight edge might be easier. Then I would use either the belt sander or bench grinder to dress and make that straight 1/8th edge Murph mentioned, been doing that step for a while. ....

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gball7
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2008-03-30          152599

Thanks Dennis,
On the topic of files, I've only ever used a wood rasp type "file". I assume they're in the same family as a blade file, but obviously too coarse for metal filing. What "size", "gauge", etc. of file do you use for blade sharpening work?
Thanks- Mike ....

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Murf
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2008-03-31          152610

IMHO, a 4.5" angle grinder is the only way to go.

All Dennis' methods will work, but none as consistently fast and easy as the hand held grinder.

Again, IMHO, it's also the easiest way to get a good result.

After much experimentation, it seems the easiest way to do it is to clamp the blade in a bench vice and hold the grinder wheel such that it is parallel with the angle the blades cutting face SHOULD have. The part of the cutting face closest to the center is usually nearly untouched and can easily be used as a guide. Then, using light repetitive strokes pull the grinder from that face (barely touching it) out towards the tip, getting a little heavier as you get to the most worn portion of the blade near the tip.

Three points are important.

One, keep the grinder moving and try not to heat the blade any more than necessary.

Two, don't worry about the cutting edge being parallel to the back edge, as long as it's sharp it's ok.

Third, the blade MUST end up balanced after sharpening. The 'balancing tool' need be nothing more sophisticated than a bolt held in your hands and through the center hole of the blade. An imbalance will cause damage to the quills (spindles) and bearings that the blades run on, as well as other parts of the drive line.

Best of luck. ....

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kthompson
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2008-03-31          152624

Quote:
Originally Posted by Murf | view 152610
Third, the blade MUST end up balanced after sharpening. The 'balancing tool' need be nothing more sophisticated than a bolt held in your hands and through the center hole of the blade. An imbalance will cause damage to the quills (spindles) and bearings that the blades run on, as well as other parts of the drive line.Best of luck.


How close to balance does the blade need to be? I would assume any amount that would cause a very noticeable heavy end would not be ok.

With the single bolt, you mean hold the bolt level and the blade vertical, correct?

Thanks Murf, kt
....

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Murf
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2008-03-31          152627

How closely the blade needs to be balanced is a gray area.

If you have a heavy duty cutter, or don't cut a lot, it's not as critical. If you have a lightweight cutter, or cut 12 hours a day it is a BIG deal.

Let me put it in easier to understand terms to understand, and without making this a physics lecture. If a 20" finish mower blade was one ounce out of imbalance, the heavy end would exert a load of about 441 pounds on the shaft driving it. Now one ounce is quite a bit, but it illustrates how fast it adds up. Also how much it counts.

A balancer doesn't have to be anything more than a bolt held horizontally between your hands, or a nail stuck horizontally into a wall.

We made up a shaft that spins on a very smooth bearing that is bolted to the shop wall, it will show a VERY small amount of imbalance because it takes so little to move it.

Another very popular (and cheap to buy) unit is a little cone that stands on a spike, you put the cone into the center hole of the mower blade and the heavy end tips down, the further it tips, the heavier it is. Low tech, but dependable and easy. They sell for about $10 at commercial mower shops, probably over the 'net too.

Bottom line, the easier the blade can spin or move on the 'balancer', the more precise it will be.

Best of luck. ....

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hardwood
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2008-04-01          152643

I use a bench grinder and a nail in the vise for balancing. The only thing I'm real sure of is that I'm getting old, but I've always guessed that 90% of the grass is cut by the first inch of the blade. I usually sharpen them about twice or until the sharpend end of the blade develops a radius of about the size of a dime then I throw them away. Frank. ....

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kthompson
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2008-04-01          152646

Frank, you are sure of more than most are.:) Too many act like youngens way too long. kt ....

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gball7
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2008-04-01          152649

Awesome responses all,
I finally read the Kubota 60"MMM deck's owners manual last night and a mill file is suggested for touchups. I actually don't own a bench vise, so I'll go out and buy one and mount it to my workbench and get started with touchup using a file. I'll also look at angle grinders going into the future. They mention balancing in the manual. The nail in the vise for balancing sounds like another great idea. Thanks guys,
Mike ....

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kthompson
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2008-04-01          152650

Mike, if you have a flat surface and a sufficent "C" clamp you can clamp the blade to that. I find that works better for me than the vise as my vice wants to hold it vertical and not flat, the angle I rather use the grinder. kt ....

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Murf
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2008-04-01          152651

Frank, you're on the right track with your guess, but the actual figure is just a little higher.

If we use a 'standard' 60" 3pth finish mower as an example;

The average tip speed is about 18,500 rpm, working backwards from the circumference, that means the blade is spinning at ~3,485.5 rpm or ~58 revolutions per second, but there are 2 cutting edges (ends) on the blade so there would be ~116 passes of a cutting edge per second.

Now, if we also assume a mowing speed of 4 mph, that means the blade is moving forwards at the rate of ~5.84' per second, or ~70" per second.

So, we have 116 blade tips passing by a given point every second, and moving forward ~70" in that same period of time. If we divide 70" by 116 passes of the blade we get 1.66" of cut per pass of a blade tip.

So there you have it, the outside 1.66" does almost all of the cutting. Or another way, 8.3% of the blade is what actually does the work.

Best of luck. ....

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gball7
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2008-04-01          152661

Good point KT. I do have a couple of those Sure-grip things that I use for light woodworking. I could use those to vise the blade flat to the edge of my workbench. I do think, as you note, that working the blade on horizontal angle could be easier than working on the vertical. It might be rainy here Saturday, but sunny and drying out Sunday, so I'm planning to take the deck off and touch up the blade Saturday, then mow Sunday! Will be two weeks Saturday since I did my first Kubota mow job, so the grass is getting really ready for another cut. The back paddock has that pink flowered heather or whatever it's called up to my high ankles. We've been blessed with such good, steady rain here in central NC lately. Lovin' it.
Mike
....

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hardwood
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2008-04-01          152663

Murf; Wow, you really like to get into the numbers, maybe you could help my wife ballance her checkbook. "Meanwhile back at the ranch", using your numbers my guess comes out almost right on the schmacker. I just love to mow grass so I only go about 2.5 mph just to make the job last longer so maybe my one inch guess is right on the mark. Frank. ....

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bvance
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2008-04-02          152667

Murf,

I emailed the Gator Blades folks and asked for Gator Blades for my Kubota MMM and they asked for a bunch of exact measurements that I supplied and here is there response:

"We offer two Gator blades for the 54" decks. One has an 1-1/8" center hole and the other has a 23/32" center hole. You would have to either have the center drilled out or have a reducer bushing made for these Gator blades to work. They are the Magnum High Lift blades at $19.95 each. "

My arbor hole on my blades are about 29/32" so I guess I could get their 23/32 and drill it out. Does that sound right? I would have thought they would have had stock blades for a major brand mower. What am I missing or what are they missing?

Thanks for your help.

Brian ....

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Murf
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2008-04-02          152670

Frank, it's the engineer in me, Uncle Sam paid a bunch to get me highly edjumikated, so I might as well use it now and then, if only for fun like that. ;)

As for your wifes cheque book, all I can say is I hope she's better at it than my ex was... "What do you mean overdrawn? I can't be, I've still got cheques left??!!". :(

Brian, you're not missing anything, they make blades for 'commercial' cutters. On the bigger machines 1-1/8" is pretty much an industry standard. The 3pth & MM mowers are not built to that 'industry standard' is all. You can try drilling out those blades, but they're made from some pretty hard steel, might be tough going. If you have access (or can mooch same) to a lathe I'd be making a bushing to take up the difference to the 1-1/8" arbor size. All you would need was a piece of heavy wall tubing run out to 0.109375 thickness with the right size inner & outer bores. Then just cut it into 3 washers.

Other than that look around, there are several others making much the same blade.

Best of luck. ....

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How do ya ll get at your large MMM blades 4 sharpening

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bvance
Join Date: Jul 2004
Posts: 280 The Great Pacific NorthWet, Olympia, WA
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2008-04-03          152685

Murf,

You are amazing! You ought to hire out your advice.

I will look around and see if I can find someone else that has the right arbor size and if not will take your advice and have someone make me a bushing.

Thanks so much for all of the help you supply to so many of us on this board...it is very much appreciated :)

Brian ....

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How do ya ll get at your large MMM blades 4 sharpening

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kthompson
Join Date: Oct 2005
Posts: 5275 South Carolina
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2008-04-03          152690

Brian, if you have them made, you may wish to have a few extra made especially if you will be who saws them to the proper thickness as the set up on this size job will be a big part of the cost. Sooner or later you will loose one. kt ....

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Murf
Join Date: Dec 1999
Posts: 7249 Toronto Area, Ontario, Canada
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2008-04-03          152696

Brian, thank you for the kind words sir.

Kenneth has a good idea. In fact, if there's a small machine shop in your area you may be able to just drop the 3 blades off to them as a 'fill in' project and have them run the holes out to the right size.

Since balance is critical it's very important that the holes be very precisely done. You would likely never get it right with a hand drill.

Best of luck. ....

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How do ya ll get at your large MMM blades 4 sharpening

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bvance
Join Date: Jul 2004
Posts: 280 The Great Pacific NorthWet, Olympia, WA
TractorPoint Premium Member -- 5 Tractors = Very Frequent Poster  View my Photos  Pics

2008-04-03          152732

Kenneth, great idea to get a couple extra, I'll do that.

Murf, I had ruled out me trying to ream out the arbor hole with a drill. I've tried similar things before and when the hole is already in something, trying to make it bigger, especially in hardened steel, just jerks you all around....would likely break my wrist! :)

Thanks guys for all your help.

Brian

....

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