Milling rare earth magnet or other magnets?

Hello, My skills as a machinist are lacking but I usually get by with my small mill and lathe by taking light cuts and cracking a book when I am unsure about
cutting speed and feed rates. I would like to mill and shape a magnet. I will be atempting this on Clausing 8520 or a light weight metal lathe. Any advice would be very helpful. What type of endmill would be recomended for this? What sort of ?
Thanks, Eddie
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mill
I have no experience with such magnets, but I'm of the opinion they will not lend themselves to machining. Grinding may work, with the use of a silicon carbide, CBN or diamond wheel. I can't help but think that between hardness and abrasion, HSS wouldn't stand a chance.
It might be helpful to provide better guidance if you suggested what you intended to do. Your mind's eye and mine likely don't see things the same way, so I may not understand your objective.
Harold
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same
My first project will be taking a magnet shaped like a small brick and creating two small shelves on the brick so it will then be shaped sort of like a surface plate with the shelf on it or the plate one might create to mount a QC tool post in the t-slot of a lathe compound. I would also like to reduce the OD diameter of a magnet shaped like a simple cylinder. I don't own a surface grinder or a tool post grinder. I do have a high speed (35K RPM?) laminate trimmer that I mount on the Aloris post on my lathe for tapering wood spindles. Even if I put a small grinding wheel on the laminate trimmer I couldn't slow down its speed easily. If the material was Al or steel I wouldn't have a problem creating these most basic of shapes even with my light equipment but as you mentioned, the magnet seems really brittle. I haven't tried ANY methods yet. I'm planning ahead. Thank You, Eddie
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simple
I'm of the opinion you can do both by grinding.

speed
for
laminate
I don't think you'd want to, either. Grinding wheels can usually be run @ 6,000 SFPM with total safety. You'd use mounted points, which will easily run at that speed, assuming they're not any larger than 5/8" diameter. You might even get away with a 3/4" diameter point, but I'd be caustion when starting it up. Don't stand in line with these wheels while they're spooling up, nor for the first minute or so. If they'll hold up for that, they're likely fine. Dress with a diamond and go to work.
You may have a hard time finding silicon carbide wheels, but aluminum oxide may work. It's not as hard as silicon carbide, which would be the best choice unless you can find CBN or diamond wheels instead. Harbor Freight offers some small diamond wheels of sorts, and they're not expensive. I'd suggest you investigate them.

the
Yeah, which is why diamond would likely be the best choice.

My pleasure. Hope you have success. Why don't you let us know?
Harold
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The answer depends on what type of magnets you want to machine. A good place to start is: <http://www.rare-earth-magnets.com/magnet_university/types_of_magnets.htm

I'll assume for now that for the purpose of this posting that you are thinking of buying some of the rare-earth magnets, since they exhibit the strongest magnetism. A quick search on Google with rare-earth-magnet +grinding brings up some interesting information: [1] <http://www.armsmag.com/rare_earth_magnet.htm : "Rare earth magnets are brittle and can be abrasively machined with coolant served to absorb heating and dust. Without coolant, rare earth magnets could crack and chip by the heat produced during high speed cutting or grinding, and the sparks contain the easily oxidized grinding dust that could cause fire!"
[2] <http://www.offshoresolutions.com/products/magnetic/rareEarthMagnets.htm "Since rare earth magnet material is prone to chipping and cracking, it does not lend itself to conventional machining methods. It can, however, be abrasively ground, but only with the use of liberal amounts of coolant. The coolant minimizes heat fracturing and the risk of fires caused by oxidized grinding dust."
The risk of fire is mainly from the rare-earth metals used; Neodymium and Samarium. In fact Neodymium is a common component in cigarette lighter/gas welding flints for this reason.
Machining and Tolerances: from [2] above: "For as pressed material, tolerance on the thickness (direction of magnetization) is ± .005. Other dimensions are ± 2.5% or ± .010, whichever is greater." gives a typical range of tolerances for commercial grade magnets.
Material Properties: Both types of rare-earth magnets are very brittle and frangible, and I would hesitate to reply on their bulk strength to hold a job down for milling. The Neodymium are often plated with nickel to improve their structural integrity. Dropping an rare earth magnet on the concrete is likely to shatter it. Wherever possible, use other means to secure your workpiece to the table otherwise you may find the magnet shattering or cracking under shock loads.
Magnetic properties: Although the rare earth magnets can exhibit great force, they don't tend to resist sideways movement that well - the friction between magnet and workpiece is key here. In addition, the greatest holding force is obtained by joining the north and south poles of the magnet with a steel bridge, instead of sticking the magnet to one piece with one pole and placing your object on the other pole of the magnet. Have a look at a magnetic table for, say, a surface grinder and you will find a series of lozenge shapes on the table which are separated from each other and the table by non-magnetic material. These provide alternating north and south poles for the workpiece. See: <http://www.rare-earth-magnets.com/magnet_university/magnetic_orientation .htm> and check with the supplier of your magnet to obtain an appropriate magnetic field that is bridged by your workpiece. If you buy cheap magnetic hooks, they often have the hook bolted or welded to a steel cup in which the magnet sits. The magnet is one pole and the steel cup is the other pole, and they connect through the item it is stuck to. This give much stronger holding power than just a magnet by itself.
If I were you, I would avoid machining the magnet if possible, and use steel pole pieces to a) provide a steady rest for the workpiece, b) protection for the magnet, and c) increased magnetic holding performance in use. The magnet can be used to provide the magnetic fields and the steel pieces for their strength and to act as pole pieces.
Health issues: If you are grinding magnets, you probably need to grind with coolant, not only for the fire risk but also to keep metal dust down. Cobalt: <http://www.atsdr.cdc.gov/tfacts33.pdf Chromium: <http://www.atsdr.cdc.gov/tfacts7.pdf Boron: <http://www.atsdr.cdc.gov/tfacts26.pdf Samarium: "Little is known of the toxicity of samarium; therefore, it should be handled carefully." <http://www.scescape.net/~woods/elements/samarium.html Neodymium: "Neodymium compounds, like all rare earth metals, are of low to moderate toxicity; however its toxicity has not been thoroughly investigated. Neodymium dust and salts are very irritating to the eyes and mucous membranes, and moderately irritating to skin. Breathing the dust can cause lung embolisms, and accumulated exposure damages the liver. Neodymium also acts as an anticoagulant, especially when given intravenously." <http://en.wikipedia.org/wiki/Neodymium Nickel: "Exposure to nickel metal and soluble compounds should not exceed 0.05 mg/cm^3 in nickel equivalents per 40-hour work week. Nickel sulfide fume and dust is believed to be carcinogenic, and various other nickel compounds may be as well. ... Sensitised individuals may show an allergy to nickel affecting their skin."
Bill Lee
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Harold and Susan Vordos wrote:

I ground a small rare-earth magnet on a carborundum wheel holding it in my hand. It sparked fiercely.
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Under the nickel plating, rare earth magnets are a brownish powder, bound together somehow, They're fragile, and crumble easily under a hammer. I'm not sure they'd machine well -- Email reply: please remove one letter from each side of "@" Spammers are Scammers. Exterminate them.
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They work the material then magnetize them. A magnetized rare earth magnet basically wants to explode into little pieces because of the magnetic force.
Larger rare earth magnets are pretty dangerous in this respect.
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On Sat, 10 Dec 2005 01:11:20 +0000, Eddie wrote:

Others recommended grinding---I always wondered about the toxicity of rare earth metals (neodymium, samarium) used in those.. http://www.rareearth.org/magnets_safety.htm seems to recommend reasonable care---it's probably a good idea to use wet process and get rid of the slurry/swarf.
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On Sat, 10 Dec 2005 01:11:20 GMT, "Eddie"

Eddie- Lots of replies about how hard these are to machine. Grinding is really the only way. The NdBFe magnets will actually catch fire and burn sort of like a fourth of july snake. Plus, they will become de-magnetized at a fairly low temperature. So you need to grind with a coolant. Also, since the the best coolant will contain water you will need to dry and oil the magnets right after grinding. Very soon after exposure to water or water based coolant the magnets will start to corrode. This corrosion proceeds fast and will ruin the magnet. ERS
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On Sat, 10 Dec 2005 01:11:20 GMT, "Eddie"
Don't. Make (unmagnetised) pole pieces instead, then stick a magnet in the middle.
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What size do you need? It may be easier to obtain than to machine.
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Been there tried to do that as well, even grinding is not what I expected..I was looking to make a smallish 1/8 to 3/16" thick by 1/2 wide by 2" long magnet to make a super skinney magnetic aquarium cleaner, and it has failed miserabley. I had a nice bunch of Rare earth magnets that I ruined in my endeavors and even paid for some of those endeavors by having a machine shop grind them.....Oh they got the magnet gorund ok, but it became very very fragile due to the naature of its construction, not from its thin section. I then spent $4.20 and bought a premade magnet of proper dimensions and now I have my skinney mag cleaner......probablay went through $100 of labor and materials with nothing to show....
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All of the aqyuarium glass cleaners I have seen are ceramic magnets, I don't think I'd risk a NIB magnet unless it was potted in epoxy.
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I have torn apart quite a few mag cleaners and all were the elcheapo types inside. The better ones made by MAG Float are rare earth types. I used epoxy resin to encapsulate the magnets I wound up usiing,in a mold I made so they are not in contact with the saltwater anyhow......
On 10 Dec 2005 16:25:17 -0800, snipped-for-privacy@localnet.com wrote: All of the aqyuarium glass cleaners I have seen are ceramic magnets, I don't think I'd risk a NIB magnet unless it was potted in epoxy.
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On Sun, 11 Dec 2005 00:00:57 GMT, snipped-for-privacy@hotmail.com (Roy) wrote:

Sure you have much to show. Experience. Something very valuable.
Gunner
"Pax Americana is a philosophy. Hardly an empire. Making sure other people play nice and dont kill each other (and us) off in job lots is hardly empire building, particularly when you give them self determination under "play nice" rules.
Think of it as having your older brother knock the shit out of you for torturing the cat." Gunner
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(Roy) wrote:

"Experience is what you get when you don't get what you really wanted."
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(Roy) wrote:

Good judgement comes experience and experience comes from bad judgement.
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Eddie,
For a little more detailed discussion take a look at
http://www.magnetsales.com/Design/DesignG.htm
Go to the "Machining of Permanent Magnets" section. I would also look at the "Manufacturing Methods" section for some more insight.
Hope this helps.
Cfs
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You might be able to find the size you want already made, here: http://www.wondermagnet.com/main.shtml They have a large variety of rare earth magnets. -- Email reply: please remove one letter from each side of "@" Spammers are Scammers. Exterminate them.
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