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 ?
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.
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
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.
I'm of the opinion you can do both by grinding.
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.
Yeah, which is why diamond would likely be the best choice.
My pleasure. Hope you have success. Why don't you let us know?
The answer depends on what type of magnets you want to machine. A good
place to start is:
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
 <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!"
"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  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.
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.
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:
.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.
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.
Samarium: "Little is known of the toxicity of samarium; therefore, it
should be handled carefully."
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
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."
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
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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
Larger rare earth magnets are pretty dangerous in this respect.
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.
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.
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....
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, email@example.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.
On Sun, 11 Dec 2005 00:00:57 GMT, firstname.lastname@example.org (Roy) wrote:
Sure you have much to show. Experience. Something very valuable.
"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
For a little more detailed discussion take a look at
Go to the "Machining of Permanent Magnets" section. I would also look
at the "Manufacturing Methods" section for some more insight.
Hope this helps.
You might be able to find the size you want already made, here:
They have a large variety of rare earth magnets.
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