Best Wheel For General Dry Grinding
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    Default Best Wheel For General Dry Grinding

    I recently ordered a small surface grinder. More to play with than anything else. It does not have a coolant setup, and it would not easily (at a glance) adapt to one without making a huge mess. Most of my mills have full enclosures and the one that doesn't keeps the floor pretty wet to the rear with its table top enclosure. Anyway, I saw a reference the other day to a wheel that was supposedly "better" for dry grinding.

    Any suggestions? Well, other than spend more money and get a different grinder.

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    Norton 32A, or 32AA, or 5SG. Any of them are far better than aluminium oxide. 5SG ceramic is the best, stays sharp longer therefore grinds cooler. 32A is great for roughing off material, little more forgiving than 5SG. If you are looking for coarse grit (36 or so) go for the 32A, 60+ grits I prefer the 5SG. Hope this helps.

    I do a fair amount of dry grinding for work and almost never reach for aluminum oxide. Wider 5SG stones can get pretty expensive so most I have are 1/4", wider we go for the 32A.

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    Well I have a Boyar-Schultz 618-2A with coolant and it does not make a mess unless you pour coolant on like a fire hose ,no real shielding . I just put it on Craigslist Phoenix the other day if you want to see how it is set up.

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    Quote Originally Posted by EOLSON View Post
    Norton 32A, or 32AA, or 5SG. Any of them are far better than aluminium oxide. 5SG ceramic is the best, stays sharp longer therefore grinds cooler. 32A is great for roughing off material, little more forgiving than 5SG. If you are looking for coarse grit (36 or so) go for the 32A, 60+ grits I prefer the 5SG. Hope this helps.

    I do a fair amount of dry grinding for work and almost never reach for aluminum oxide. Wider 5SG stones can get pretty expensive so most I have are 1/4", wider we go for the 32A.

    The "A" in 32A a means aluminum oxide.

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    I'm not sure 5SG wheels really shine until you get into production grinding and can take advantage of more grinding between dressings. If you have the money, hey, go for it. Note that Norton recommends their own special dressing tool for the SG wheels, though I've always used an ordinary cheap one. Not sure what the difference is. My experience is wet or dry is very much material dependent. Some things just like lubrication, even if it's just a brush or spritz of oil, water-based or even WD-40. I've never had any issues with inexpensive white aluminum oxide wheels, wet or dry. The real trick is not over dressing them, which gives you a fussy wheel that tends to burn. The hardness of the wheel should also be suited to the material if possible. Fine wheels are often a mistake as well. If you can't get a good finish with a 46 grit, something's wrong.

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    Yeah dress fast for rough grinding. It will leave a coarse finish but boy will it rip the stock off and cut free and cool. Make sure you're not using an old rounded nub of a diamond too. A fresh one is worth the cost several times over. A dull diamond will start you off on the wrong foot with a slightly glazed wheel. Slow the dress down for finishing; how slow you'll figure out as you go. Too slow and you'll have loading, wheel bounce and burning.

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    Default Worn dressing diamond re-mount

    Quote Originally Posted by eKretz View Post
    Yeah dress fast for rough grinding. It will leave a coarse finish but boy will it rip the stock off and cut free and cool. Make sure you're not using an old rounded nub of a diamond too. A fresh one is worth the cost several times over. A dull diamond will start you off on the wrong foot with a slightly glazed wheel. Slow the dress down for finishing; how slow you'll figure out as you go. Too slow and you'll have loading, wheel bounce and burning.
    I totally agree when it comes to a dull dressing diamond. A diamond has more than one facet and can be remounted. Remove the diamond from the mount, then turn it so a sharp facet is exposed on top. Reset it using silver solder and a torch. Cool in the air.

    Roger

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    Quote Originally Posted by tdmidget View Post
    The "A" in 32A a means aluminum oxide.
    A quick history of aluminum oxide abrasives:

    The white aluminum oxide abrasives are pure alumina and do not contain titanium or iron oxide impurities. The grey, brown, blue, and red aluminum oxide abrasives contain iron, titanium, and for the red wheels chromium additions. The abrasives are made by flash cooling molten alumina on a chilled conveyor belt. The flash cooling is required to produce small alumina crystals. The cooled chunks of alumina are crushed to the desired grit size. This process originated in the early 1950's. It was a major improvement over the original process developed in 1904. The earlier process produced 10 ton blocks of alumina by resistance heating the raw starting materials. The blocks were slow cooled over several days and then broken apart and crushed to the desired grit size. The slow cooling produced large crystals.

    A 46 grit abrasive grain will have on average three crystals of alumina. The white alumina grain is not durable and breaks apart with relatively little pressure. Many years ago it was the first choice for dry grinding due to its rapid breakdown and the resulting sharp fractured remaining grain. The pressure that is exerted on the grain increases as the grain surface becomes dull. The grinding wheel tends to be self sharpening assuming that it also has a low grain bonding strength. This would be roughly a J grade. The grey, brown or blue grinding wheels containing the iron and titanium oxide impurities have a much higher grain strength and require much higher pressures for the grain to fracture. The fractured grain does not have the sharp edges of the white aluminum oxide. The red wheels contain chromium oxide which increases the grain strength slightly while still maintaining the self sharpening characteristic.

    There are also alumina-zirconia abrasives which are used in cutoff and snagging wheels. These are very sharp abrasives which erode rapidly.

    In the 1960's Norton developed the 32 A single crystal per grain abrasive. This abrasive is produced by pre selecting the grit size by sorting through the
    bauxite starting material by size. A batch of 46 grit size alumina crystals will be selected, for example, and then run through a furnace to fuse the internal fractures within the crystal. The abrasive produced does contain the original iron and titanium impurities of the raw alumina.

    The 32A abrasive grain when it becomes dull will fracture along one of the many crystal lattice planes. The grain is self sharpening and there will be a large number of grain fractures before the grain is consumed. The fracturing process requires higher pressures than the white alumina oxide but the grinding wheel will have a much longer life. This abrasive would be the first choice for a general purpose wheel.

    The SG or the roughly equivalent 3M cubiton abrasives introduced in the early 1980's are microcrystalline alumina grains produced by a chemical process. Each grain contains thousands of crystals. The process involves producing a gel which contains the micro crystals. The low strength gel is crushed to produce the desired grain size.
    The gel grain is then run through a flash furnace process to sinter the grain. The waste dust from the crushing process can be recycled back into the next batch of gel. It is a energy and material efficient process.

    Each microcrystalline grain can be fractured thousands of times before it is consumed. The only difficulty is that it requires a very large pressure to break off a micro crystal.

    The solution to the problem is to mix the seeded gel abrasive with the easily fractured 1950's abrasive. The mixes from Norton are SG at 10%, 3SG at 30% and 5SG at a 50% mix. Grinding application with large wheel contact areas will use the lower concentrations of the seeded gel abrasive.

    There are a number of grain geometry variations possible with the seeded gel abrasives. The Norton Targa wheels, for example, use a extruded gel grain that is 10 times as long as it is wide. This produces a very porous light weight wheel that is stronger than a conventional grinding wheel. The wheels can be used at surface speeds significantly higher than the 6500 ft/minute of the conventional abrasives.

    The seeded gel wheels will still require high wheel pressures to be self sharpening and would not be suitable for some grinding applications.

    When the grinding operation is less than ideal the abrasives will not be self sharpening and you will need to use the diamond dresser to pull out the dull grain and expose the next layer of abrasive. This will occur if you are working with a grinding wheel pressure that is too low for the abrasive being used.
    Last edited by Robert R; 04-08-2020 at 03:52 AM.

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    One makes a cost evaluation and justifies a more expensive wheel.
    For short run jobs work how often the wheel is altered makes a big difference.
    How many wheels hanging on the rack makes a big difference.
    Paying 20x the price likely can be justified in some shops and certain work.
    Need to dress a form and lose ¼ of wheel for a few parts can’t justify such a wheel.
    So, ceramics are good where they save dollars’
    I like white wheels mostly, I have had some jobs where pink wheels were better for running cooler, have one job where a 46 k brown wheel would ruin the edge that had a .005 to .007 radius corner running dry and a 46k white wheel did not. Had a job where a ceramic was better, but not better enough to justify the price. It mostly depends on dollars. For my grinding now that I’m retired of one-ups and few ups to about 300 parts I mostly use white wheels.

    For the OP I would recommend a small mist collector and design a box-in at the go direction of his grinder. Containing the grinding dust is a good thing and some work needs coolant/wet.

    Right now, a 46 J white Carborundum is my favorite for hard and medium hard steel for running dry. (AA46 J8 V-46)
    Applications | CARBORUNDUM GRINDING WHEEL CO.

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    so the color of the wheel is directly related to the type of abrasive used? no dyes involved?

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    QT Dian: {so the color of the wheel is directly related to the type of abrasive used? no dyes involved?] true.

    Brown is usually a tough wheel more for longer life that cool grinding. pink are often friable grains that may chip off and give another sharp edge before the bond lets lose. White wheel can also be friable to chip off and give another cut
    Black wheels are hard and much like green wheels (SC,Silicon Carbide ) hard enough to abrade carbide. Blues are ceramic good/great for hard steel but expensive. Orange wheel are/may be made of clay and are often fine grain for super finishing. Some grits are coated so to give them a varied ability to the bonds ability to hold each grit. Some times the cooling process is used to make the hardness of the wheel. Even the kind of glass and clay that makes the glass is a trade secret of a wheel manufacturer. Big science.. The spacing between each grit is important to wheel life, surface finish,heat or cool and other qualities.

    Likely there is a internet site that explains this but a lot is close held by each abrasive manufacturer trying to make the better wheel, i used to have the formulas sheet on some wheels but they may still be out in the shop or tossed. Not much good nowadays. I used to be in a position to ask a wheel manufacture to make a special non catalog wheel.

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    thanks RobertR, nice historical summary. how is Cubitron II made? same "gel" proces? (and yes, it really should be called Triangulon )
    Last edited by cyanidekid; 04-09-2020 at 08:32 PM.

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    Quote Originally Posted by tdmidget View Post
    The "A" in 32A a means aluminum oxide.
    Yes, you are correct, I should have said "far better than the standard white aluminum oxide"

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    Quote Originally Posted by cyanidekid View Post
    thanks RobertR, nice historical summary. how is Cubitron II made? same "gel" proces? (and yes, it really should be called Triagulon )
    There are a number of different processes for producing micro crystalline abrasive. 3M was the first manufacturer to file a patent and begin production in 1981. Their patent was specifically for abrasives used in sandpaper. Norton followed in 1982 with a seeded gel process that did not infringe on 3M's work. Norton's abrasive patent covered both sandpaper and grinding wheel applications.

    When 3M began selling the cubitron abrasive to wheel manufacturers Norton filed a patent infringement claim. Eventually 3M paid Norton a large settlement to be allowed to sell the cubitron abrasive to all interested customers. If you buy a ceramic abrasive wheel in the US made by a company other than Norton it will have the 3M product. The Cubitron abrasive has sharper edges and requires less applied force to self sharpen. The disadvantage is that it also has a shorter wheel life.

    Over the last 40 years there have been over a hundred additional patents. You can search on freepatentsonline.com using the keywords from the earlier patents. There will be patents on the cubitron II abrasive and on the Norton extruded SG abrasive. The 1980's processes described below for gel derived abrasives are obsolete. They do provide the background for understanding the more recent work.

    If you would like to know more take a look at:

    3M 1985 patent 4518397 Has the details of their aluminum oxide- zirconium oxide-magnesium oxide micro crystalline abrasive process along with photographs and grinding performance tests

    3M 2016 patent 9446502 Method for producing triangular abrasive shards

    3M 2001 patent 6277161 A process for producing submicron size crystal abrasives derived from alumina gels

    Showa 1993 patent 5215551 A variation of the 1985 3M process that generates a 0.4 micron micro crystal compared to the earlier 3M 10 micron crystal size

    Norton 1963 patent 3646713 This is the 32A abrasive

    Norton 1986 patent 4623364 This is the seeded gel process. It appears that Norton stumbled on this process by accident. The seeding crystals required for producing the abrasive originate from the alumina grinding balls used to mill the gel. The crystal size is 0.4 microns. The abrasive does not require the addition of zirconium oxide.

    Other comments:
    The color of the abrasives can be deceptive. The Norton SG abrasives are either white or blue. This appears to be a marketing strategy to distinguish between two grain bonding formulas. Norton provides no details on their website.

    The patents are useful if you are interested in numerical comparisons of the different abrasive types. This kind of information is omitted from the marketing literature in anticipation that the customer will buy a trial wheel and do their own research.

    The color of the older abrasives can provide a clue as to their heat treatment. The 3% titanium dioxide present in the fracture resistant grades of abrasives is initially brown. If the abrasive is furnace annealed to remove the fractures in the alumina crystals caused by crushing the color will change to blue-gray.
    Last edited by Robert R; 04-09-2020 at 11:31 PM.

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    very interesting. i alwas assumed the color was just a way to distinguish between wheels and dependend on the manufacturer. well, at least concerning norton sg wheels, this seems to be the case.

    edit: i have a blue od grinding wheel. if i look up the product number i see it in blue but also in yellow.

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    Interesting stuff! As I've said, the benefits of the SG wheels elude me and I wonder if the bit about more wheel pressure is why. Maybe SG wheels aren't a big improvement for small 612 type grinders, compared to a more rigid machine with more HP?

    Surface grinding is learned from the more experienced people in any given shop. It's treated as more of an art, with formulas and rules rarely given, though they do exist if you search the 'net or read some of the old books. I'm convinced that much of what people believe is sub-optimal at best, but because they've been doing it that way for 30 years, there's no changing the thinking. Most everything I was taught over the years about dressing a wheel has turned out to be wrong. Only a bunch of experiments, combined with the use of a profilometer, has led me in the right direction. Same thing with balancing. If you're not doing it, you're not getting the best out of the wheel.

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    Quote Originally Posted by Conrad Hoffman View Post
    Interesting stuff! As I've said, the benefits of the SG wheels elude me and I wonder if the bit about more wheel pressure is why. Maybe SG wheels aren't a big improvement for small 612 type grinders, compared to a more rigid machine with more HP?
    That is the idea. A toolroom grinder wheelhead may weigh less than 400 pounds. That weight limits the maximum pressure that can be applied to the grinding wheel.

    The manufacturers should be publishing charts displaying grinding depth, wheel width, wheel travel speed, coolant type, steel hardness and abrasive grit size verses grinding wheel pressure. The chart would then include the pressure operating region were their wheels are capable of self sharpening. It is easier to let the user do the trial and error work.

    A wheel used for finishing needs to be self sharpening at very low wheel pressures.

    The more recent 3M abrasive described in the 2001 patent is designed for a wider operating range.

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    Hell, my whole Boyer-Schultz 612 doesn't weigh a lot over 400#! That's also the reason balancing is so important.

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    "When the grinding operation is less than ideal the abrasives will not be self sharpening and you will need to use the diamond dresser to pull out the dull grain and expose the next layer of abrasive. This will occur if you are working with a grinding wheel pressure that is too low for the abrasive being used."

    does the diamond not cut/fracture the grains?

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    Quote Originally Posted by dian View Post
    "When the grinding operation is less than ideal the abrasives will not be self sharpening and you will need to use the diamond dresser to pull out the dull grain and expose the next layer of abrasive. This will occur if you are working with a grinding wheel pressure that is too low for the abrasive being used."

    does the diamond not cut/fracture the grains?
    Dull grains and simply loading up with particles on material being stuck/loaded on the wheel.
    Aluminum is an extraordinary example with loading quickly and with serios consequences.
    Coolant can sometimes reduce loading of some materials.

    Q:[does the diamond not cut/fracture the grains?] It can with certain grains and others the diamond just breaks them away from the bond (the material holding grits together.)

    Crusahable wheel often hold up better than diamond dressed wheels..They have a bond that is made for crushing with a roller dresser. Most/many non crushable wheels might break with rying to crush them.

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