Great thread! I've been using the cone balancers for most of my jobs, and I'll agree that they can never be entirely precise, I once tried to balance the 32" single blade on a Snapper RER, and I had a heck of a time with a cone balancer, I eventually had to resort to putting a screwdriver in a vice, levelling it off, and hanging the blade from that. I highly enjoyed your analytical approach to the issue of a perfectly balanced blade, and in this case I'm sure $92 will go a long way in protecting the life of those precious mandrels. I rebuilt all of the lawn tractor mowing decks I have as a precaution, and I'd certainly hate to have all of those shiny new bearings shred themselves because proper care was not taken to balance the blades.

 

Well..... um.... ahhhh.... I guess since I own a JD 48C deck AND the aforementioned and technically derided "plastic cone balancer" I will have to reply. IF I were balancing mowing turbine fans instead of "mower blades" I really might opt for the somewhat expensive "hi-tec solution" outlined in the above revue.

However, since my deck is designed and constructed by John Deere I can be totally assured that my "plastic cone balancer" is within the expected parameters of JD's engineering expectations of home maintenance balancing efforts by a normal individual. John Deere assuredly selects only the finest and typically roundest of hardened ball bearings and mostly symetrically machined bearing races. I'm totally sure that both items are manufactured from fully tested and proven metalurgically excellent materials for long life in high speed rotational service. (When maintained/lubricated as instructed by the visually illustrated and well edited owner's operational manual.)

As the pivot point of a plastic (cheap conical) balancer is made of "space age petrochemical plastics" it is thus inherently self lubricating and free of friction to the amount of weight applied in the balancing proceedure of a simple "mower blade". I will even go so far as to say that I have had no complaints whatsoever after balancing the front wheels of my wife's candy apple red semi-custom 4 wheel walker (w/seat and hand brakes) without hesitation using the same device. Even on the most uneven of shopping mall floors the wheels continue to track true and totally free of vibration. With several years of these positive results I can feel totally assured that my mower blades (OEM and specialty GATOR brand) will remain vibration free to the extent and degree required by the original equipment spindles.

Disclaimer: I am in no way connected nor am I reimbursed by any cheap-o plastic balancer manufacturer, their advertising departments or distributors.

 

Yup, that's the way to do it. :trink39:
I am going on my tenth year with my Scag turf tiger 60" deck. All original bearings and spindles. I have never balanced a blade. Common sense prevails in this household.

 

I love precision, but that's a lot of money... if I had a small engine shop, that'd be another issue. I'm just a DIY-er though.

 

I thought about that for some time; then realized that I just paid well over 20 times that for my LT, and so I decided to rely on less art and more on precision, and that I would be sharpening blades for more than just one mower. I'm about ready to offer a service in the community and pay for this capability in a couple of weeks.

 

its true one has to love precision. and be analytic. there are a great many blades that have survived lesser methods to be sure, without blowing up. with care the lesser cones certainly work out for a lot of folks. im just not one of them ! im sure a lot of bakancing happens with the nails too

 

I think my head just esssploded...

Mike

 

While I'm not able to justify getting myself one either, I can certainly respect a quality tool and admire those who demand perfection like that.

Who wouldn't like to take a freshly polished blade and feel/hear the satisfying snick of a powerful magnet securing it in place before giving it a good spin on a precision bearing assembly and watching it whir?

Thanks for sharing with us!

/WW

 

One thing that I do see wrong with the pictures besides the dirty blade. The fixture would have to be sitting on a precision surface plate leveled for accurate measurements to be made. Otherwise it's not any better than a cheapo balancer.:banghead3

Maybe if I were in a blade balancing business, hmm. Precision balanced for BIG $$$. :fing02:Thanks for the idea.

 

You're right that a couple of the pictures show a dirty blade, and that was explained suitably. The first step is to put a wire brush on the angle grinder and clean things off. then follow with 60 grit flap disk and a file.

The comment about a level surface plate is not accurate. The fixure doesn't "sit" (horizontally) on anything -- it is mounted once to a vertical surface level to within 5 degrees of plumb, using carpenters level. Thats the advantage of this particular solution: once the fixture is mounted, then all of the balance imperfections are manifested as rotation around the low friction bearings. The cheapo balancers are just as innacurate no matter how carefully they are mounted, due to friction.

 

that,s all well and good.but what about all the grass dirt and all the rest that gets caught on the blades. what happens to all that balancing .but very well written.sorry.

 

This is the conclusion I came to several years ago while sharpening/balancing blades. Thirty minutes into mowing I may have a few ounces of debris adhering to the blade. My fine balancing job is shot. So maybe the next step is to coat the blades with graphite or silicone to reduce sticking grass, and to do a better job of cleaning the deck and blades after each use.

As to the hundred dollar balance jig; it can't hurt, it's great for peace of mind, it is likely a once in a lifetime purchase, each of us does what makes us most enjoy our equipment.:fing32:

 

Thanks for that, dlleno! I'm curious what methods you found the shops using.

Anyone try using a tire spin balancer?

 

The shops locally that I interviewed all used a nail in the wall. honestly I suspect the cheaper cones are not that much better than a finishing nail and a drop of oil, and would probably work good enough especially for smaller blades with round mounting holes. Even in my case (star mount), the nail method showed balance -- it was just not very sensitive to imbalance as I illustrated.

Considering the spin balancer really brings the right issues to the front in the case of blades on a mower. first of all, the mount point itself on a car tire is far more precise, and the effects of imbalance is vibration in the vertical direction (the seat of your pants). weights are added in strategic points around the tire.

in the case of the mower blades, the blade edge itself is the only thing you can adjust, and the mount point is much less precise. Also, the vibration is lateral, and absorbed by deck suspensions and normally not felt at all in the case of an LT, for example. smaller push mowers, not so much of course, but the blades are typically shorter anyway.

In the case of a mower blade, the mount point itself has some slop (tolerance) built into it (you can wiggle the blade before tightening things down...), and this imprecision is tolerated by the spindle/mandrel assembly. When we balance blades, we are just insuring that we do not introduce any additional imbalance not accounted for already by the designers.

 

And we all should remember that there are only two (2) days per year that an accurate blade balance can be achieved, the Summer or Winter Equinox. Might as well forget it the rest of the year.

Has anyone tried balancing a sickle bar blade on a standing broom?

 

I think the gunk stuck to the blade is a factor, but my hunch is it does not play as much of a factor as the metal. When your cutting grass the gunk sticks to the blade yes, but I would think that for the most part it sticks uniformly. Only way to really tell is to sharpen and balance the blade then mow a good stand of grass then take the blades off and put them on the balancer. If it remains well balanced then I think it lends even more credibility to the balancer.

In my mind, there is nothing wrong with quality and craftsmanship. Some people are content with their walls being 1/2" out of plumb, others not so much. The ones that are perfectly plumb are indicative of better craftsmanship. So it goes with the balancing of blades. IMHO. :thThumbsU

 

Interesting. I tend to skip the whole middle section of your process though. I have a nail sticking out of the side of my bench, and hang the blade on it. The side that drops gets a couple passes on the grinder until it stays level.
There are two things to keep in mind as well: The first time you ding that blade, all the work done is lost.
It's usually an impact that takes out the spindle. Even the weakest spindles can hold up to an improperly balanced blade (within reason), but I have had an AYP aluminum spindle broken by hitting a 2" rock.

 

Interesting. I tend to skip the whole middle section of your process though. I have a nail sticking out of the side of my bench, and hang the blade on it. The side that drops gets a couple passes on the grinder until it stays level.

yes, indeed. especially for round mouting holes, a smooth finishing nail with a drop of oil is probably just as good as any of the less expensive cones. its just not very sensitive. thats the only reason I decided to spend the $92 -- increased sensitivity to imbalance.

There are two things to keep in mind as well: The first time you ding that blade, all the work done is lost.
It's usually an impact that takes out the spindle. Even the weakest spindles can hold up to an improperly balanced blade (within reason), but I have had an AYP aluminum spindle broken by hitting a 2" rock.

yes good point about what really takes out a spindle. What I'm really refering to is the effect of routinely and consistently imbalanced blades on the long-term life of a spindle.

Naturally, the system is able to accomodate small dings, and one should remove the blade and re-balance after hitting something big. But genearlly, my point is that the purpose of balancing is to eliminate the variable of the blade itself from the equation which has a great many other factors.

the other thing I like about this jig is the indicator rod that allows you to detect even slightly bent blades. Its possible that a blade could be sharpend and balanced after hitting a large rock, but still could be bent in which case you might not know it until your grass started to look uneven.

My question for the original poster is "How do you know the blade hub is balanced as precise as you have the blades?"
Dave

In my opinion, what we have to accept here is that the blade hub, the spindle, the blade mount point itself, and even the pulleys were all designed within their respective tolerances, and that the system is designed to work within the tolerances that are known and accounted for by the designer. A balanced blade is something that the designer has to assume, and over which h/she has no control. So we are motivated to to minimize the contribution of the blade itself to the entire system.

we wouldn't want to add an imbalanced blade to an already imbalanced hub.

 

My question for the original poster is "How do you know the blade hub is balanced as precise as you have the blades?"
Dave

 

Years ago I wondered if blade imbalance was the cause of deck pans cracking around the spindle housings. Using brass to braze the cracks and balancing the blades proved this was the cause as the 2 decks I did are still going strong. I would have used steel to weld but wanted to test my theory.

If you are a woodworker you are familiar with the pilot bearings on a router bit. Most mower blades have a hole that you can find a bearing to match. Mount the bearing on a horizontal stud, hang the blade on it and you have a very accurate balancer. The bearing lubricant is very light so it takes very little weight to turn it.

Before I remove a blade I check one cutting height, rotate 180 degrees and measure the other. If not the same the blade or spindle is bent causing a dynamic out of balance condition that no amount of grinding will correct.

I went overboard making a heavy stand with a square post so different sized bearings could be mounted on the 4 sides. I learned the 3 adjustable feet on the stand to precisely level the bearings are not necessary.

This statically balances any blade. Back on the mower there will be no left to right so to speak out of balance condition.

If a blade is bent it will not be balanced dynamically but can be perfectly balanced statically. Back on the mower this condition causes the blade to vibrate up and down or wobble.

A 2" blade with a 3/4" mounting hole hung on a nail has 18.75% of the blade's weight acting as a pendulum masking much of an out of balance static condition simply because the pivot point is not in the center of the blade.

For comparison an auto wheel and tire which is much heavier that is out of balance by 1/2 oz is easily detected by a technician's road test if they specialize in that.

A 1/2" x 3" x 30" Gravely brush blade now coasts for about a minute after the tractor is shut off with absolutely no vibration. With background noise it is dangerous because you can not hear the drive gears turning.

Have found dull blades to still be balanced at resharpening time even before cleaning. After a cleaning and my sharpening they are out of balance. An extra pass or five of the grinder sometimes on one end is required to rebalance.

Have found all new replacement blades to be well balanced so far.

Garry

 

Before I remove a blade I check one cutting height, rotate 180 degrees and measure the other. If not the same the blade or spindle is bent causing a dynamic out of balance condition that no amount of grinding will correct.



Garry

I just stack all three blades together and which ever one is bent will not match the other two.

 

Go one step further and pop the seals on your balance bearings and wash out all the grease.. Put in a few drops of light oil...

 

Try GOOGLING something called "spectral vibration analysis" and you will quickly realize this is a joke.

I have tracked and balanced 100s of aircraft propellers and helicopter rotors over the years and this whole discussion is just comical.

Non of the overkill methods take into account the harmonics or shock loads encountered in the everyday life of a mower blade. While it is true a mower blade should approximate a statically balanced state at the time it is installed that starts to change as soon as it hits it's first blade of grass and wear takes place.

A bit of serious research into the intricacies of vibration, causes and effects would be a good starting place.
http://en.wikipedia.org/wiki/Vibration
http://en.wikipedia.org/wiki/Vibration_of_rotating_structures

Yeah, it's all math and science stuff! There are numerous books written on the topic as well.

I do have a Chadwick-Helmuth system available. At $30K I guess everyone should run out and buy one. :ROF:ROF

OR, for $4 I have a cheap plastic "cone on pivot" that will give me a close static balance and just call it good. :dunno:

 

yea I do believe it is clear that complex vibrations are not the issue. Its the static balance we're after, and one is free to determine what is requried in order to reduce the contribution of the blade's static balance as far as one deems necessary, and to introduce as much precision into the process as needed, for the cost that is acceptable.

One point that should be made here, with respect to this veritically-mounted jig, is that the level of precision I illustrated (perfectly horizontal blade) is neither warranted nor recommended, because perfect horizontal orientation is the most sensitive position: Only a few strokes of the file are detected, which is clearly over kill and would cause most anyone with a lick of sense to roll on the floor laughing as well. As the blade rotates on the jig, the normal force (what pulls one side down, due to imbalance) is overcome by the friction in the bearings and rotation stops. Even the instructions state that some rotation is acceptable I just don't remember how much, exactly.

This method is just a practical way to improve the precision and sensitivity of nails and small cones, improves repeatability and reduces the level of art required. The balance step is quicker, easier, and quite an advantage especially if you are balancing more than two blades per year.

For me personally I find that the small cones offer no practical advantage over a good finishing nail, and both methods are blind to a certain amount of imbalance. Beyond this particular $92 jig, the solutions really get esoteric.

Anyway, my goal was to show how one can really drive to zero the static balance contribution of the blade at sharpening time. I do think it would be amusing to play it the other way -- to see how little one can get away with, and what the results are. For example, I used to balance push mower blades with a finger and a screwdriver and lived to tell about it. One can mow a lot of grass and hit a lot of stuff, and still keep cutting grass...

 

OK, I think we've got this end to end balancing thing knocked... Now, what about balance from one side of the blade to the other? How "important" is widthwise balance in the entire spectrum of rotating blade mass? If my blades are perfect lengthwise I sure want them to be in balance crosswise as well!

AND, in my case, I certainly want to make sure my blades are truly centered on the spindle bolts when I tighten them. Afterall, there is a significant space in the blade hole around the bolt. Anyone install micro arbors to assure the blade is running it's true center of balance on the spindle bolt or spindle shoulder? Yes, and who can assure the sympathetic vibrations of a triple blade belt driven deck can be controlled even with precision balanced blades... Oh the disturbing ramifications of runaway manic mechanical obsession!

Tomorrow, a discussion of bivalve torque and it's effect on lower shell evolution.

 

AND, in my case, I certainly want to make sure my blades are truly centered on the spindle bolts when I tighten them. Afterall, there is a significant space in the blade hole around the bolt. Anyone install micro arbors to assure the blade is running it's true center of balance on the spindle bolt or spindle shoulder? Yes, and who can assure the sympathetic vibrations of a triple blade belt driven deck can be controlled even with precision balanced blades... Oh the disturbing ramifications of runaway manic mechanical obsession!

I usually do make a tight fitting spacer to get rid of the mount variable.

 

well.... the term obsession, as well as thread drift, come to mind but I assume you are serious and not being rhetorical!

I acknowledge that my suggestion here to introduce greater precision into the static balancing process has generated some interesting implications of esoterica that I never intended -- but assuming you are serious here I'll weigh in:

the things that I'm out to optimize are the things that the origional designer placed into my control, namely static blade balance. Beyond that, if there is compelling reason to change something, then I am modifying, not maintaining -- which is an interesting topic to be sure, but a little out of scope in my opinion, at least for my original intentions for this thread. If the design is that bad, then I should have bought something else, I guess

that said, since the primary motion of the blade is to rotate about its center, I suspect that non-homogenious materials, irregular densities and other esoterica within the width of blade material itself are, well, either unimportant or already accounted for by the blade manufacturing process itself. no reason to re-design the blade is what I'm saying, unless of course you are building your own!

I touched on the factor of slop/tolerance in the blade mounting point, earlier. my take here is that I can't control that, except to try and center the blade during install (which I do), but frankly the original design expects such slop and builds in this tolerance. To me, the presence of slop here means

1. worry more, not less, about blade balance.
2. the slop is within the original design intensions, so trying to reduce it won't do any good.

As for the other dynamics of rotating blades, I quick look at the blades themselves will reveal their original intentions: they appear to be stamped out by the thousands, and the center hole is cut with a die of some sort. In any case, not exactly your best example of a machinist's pride of dimmentional precision. This tells me that all those dynamics are either unimportant or accounted for, and that my job is to not worry about anything except static balance.

Harmonic activity relating to multiple spindles matters is a similar don't-care, but it is amusing detail that one can ponder while mowing Fortunately for me I have to worry only about two of them, which is enough for both sides of my brain to handle while I'm out riding.

 

I've been reading thru these post and a lot of it seams to make sense but it does seam to me to be a lot of work for nothing.

I have been mowing lawns for over 50 years and I have never bothered to balance a mower blade in all that time and I can't think of any problem that has been caused because of an un-balanced blade ?

Of coarse I'm certainly no expert on mower blades, that is just my own personal experience.

 

I've been reading thru these threads and a lot of it seams to make sense but it does seam to me to be a lot of work for nothing.

I have been mowing lawns for over 50 years and I have never bothered to balance a mower blade in all that time and I can't think of any problem that has been caused because of an un-balanced blade ?

Of coarse I'm certainly no expert on mower blades, that is just my own personal experience.

this is a very fair question. I've been mowing for nearly a half century as well, and as I mentioned earlier I balanced push mower blades with nothing more than a finger and a screw driver, and in many cases not at all.

That was when my blades were shorter, narrower, and when I bought old mowers at yard sales and would often let more than two years elapse between sharpenings. my motivation this time is a bit different, since I paid one or two hundred times as much for my LT as I did my first used lawn mower. even after adjusting for inflation! So I tend to follow the mfg recommendations, at least those that make sense (speaking of not making sense. one manual says you can only sharpen a blade once before it needs to be replaced). lol well, what else are they going to say when they don't want to be held liable?

But the (common or uncommon, TBD!) sense in me remembers push powers that vibrated, some more than others, and that the blade was attached directly to the engine crank. reducing vibration was, and still is, my main objective, even if I can't feel it in the seat of my pants, because things that don't shake last longer than things that do. so I basically took the mfg recommendations, noted that they made sense because I don't want things to shake, and then made the best of my ability to make sure that if things vibrate or the spindles wear, it would not be becasue of the blade's static balance. I suspect that the worst enemy is continuous and progressively worse out-of-balance from repeated sharpenings, where the spindle bearings would be loaded more and more.


I'd suggest if you want a crude adjustment, get a finishing nail or a small cone and call it good. Whether it is so or not you won't know for a long time anyway. If you really want to eliminate blade balance as a factor, then you've got to get more serious -- and even then you won't know for a long time if the effort was necessary! Proably today's decks, especially the lower cost ones, are not made as robustly as those 40 years ago, which means that tells me spindles will be happier longer if the blade is balanced.

But thats just my opinion; without supporting data, all the balancing efforts, from finger to the expensive jigs, are more about the owner either doing what they were told without understanding it, or just feeling good and believing in his/her approach that is best for them. We're not likely to ever get supporting data because it would take too long and require too much control in an experiement to produce anything useful.

I suspect that the situations most likely to benefit from careful, precise balancing are those where one or more of the following is true

1. the interest is in long term cost of ownership
2. there are mulitple blades in the deck
3. the blades are long.
4. the deck is consumer grade, not professional

all of the above apply to me.

 

I hoist it up and grind away... I dont even remove the blades...
never had a problem with one spindle bearing in my life of 60 years...

 

I like it. maybe your spindles are just as robust as the axle from which you are hoisting your tractor! I don't think my LT could tolerate being hoisted like that and suspect that today's spindles found on sub-$2000 LTs sold in big box stores are not quite that durable.

 

Gravelys actually enjoy being hoisted like that!

 

Once you use the blade and it gets any dirt and/or chopped vegetation stuck to it, it is no longer in "perfect balance". You would have to stop and clean the blades every few seconds of cutting to maintain "perfect balance" for any amount of time that would actually make a difference over a less precise balancing method. Heck, if you use a cheaper, less precise method to balance the blades, and then use them to cut, and they get some dirt and/or clippings stuck to them, they might end up being perfectly balanced for a few seconds of use after a minute or two just like the first few seconds of use of a perfectly balanced set of blades.

 

There are two falacies here

1. considering how fast the blade spins, the accumulation of dirt and debris will tend to be uniform, and especially since organic matter is lighter than the steel in the blade, such non-uniformity is probably not significant especially if the blade is balanced to begin with. this is a hypothesis that should be tested though; perhaps we can collect more data here as the season progresses.

2. the fact that other tolerances (including the possible accumulation of debris on the blade) are present in the system should convince us to eliminate or reduce the ones we have control over, not to intentionally introduce variability.

perfect balance can never be obtained, and the excersize is not so much about acheiving perfection as it is about finding the method that is good enough, using measurement indicators that you trust and can be repeated. In the case of this particular device I am using, I find that I just have greater control, sensitivity, repeatability, and therefore greater and more accurate visibility into what is going on.

 

first data point: after 45 min mowing

ok ttftt I took her out for the first mowing of the season. 45 min overall time on the counter; mixture of leaves, grass, and light brush. grass was not very tall, but whatever accumulation of organic matter occurred on the blades was astonishingly uniform, and undetectable with the crazy esoteric overkill balancer.

perfect balance maintained. Here's the blade

need to test of course with heavier/taller grass.

 

Re: first data point: after 45 min mowing

ok ttftt I took her out for the first mowing of the season. 45 min overall time on the counter; mixture of leaves, grass, and light brush. grass was not very tall, but whatever accumulation of organic matter occurred on the blades was astonishingly uniform, and undetectable with the crazy esoteric overkill balancer.

perfect balance maintained. Here's the blade

View attachment 205468

need to test of course with heavier/taller grass.

I know this would be a lot of work for your personally, but it would be incredible if you could chronicle your findings thoughout the season. We all have our theories, but there is nothing like a facts from a well controlled study.