# Machining neodymium magnets



## deverett (Mar 29, 2010)

Is it possible to machine neodymium (rare earth) magnets? If so, could you please give me some tips on how it is done.

I haven't attempted it yet, but I have a project in mind that would need a curve put on the flat ends of a magnet. Think drilling a cross hole in a bar of brass, putting the magnet in and machining the end of the magnet to conform to the diameter of the bar.

Dave
The Emerald Isle


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## mklotz (Mar 29, 2010)

I suspect that a lot of those magnets are sintered and, while I've never tried it, probably machine like a pink pearl eraser that's been left out in the sun for a year.


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## ksouers (Mar 29, 2010)

Dave,
I would suspect you don't really want to machine it. Will drilling the rod deep enough to bury the magnet suffice? You could then fair the surface with thickened epoxy.


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## Kermit (Mar 29, 2010)

Put a 'cap' on them. Not possible to machine them after they are magnetic. Neo's are very brittle, pressed powder, baked with a binder. Probably not possible to machine them at all. You have to start from scratch with a die, or mold them into shape.


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## mklotz (Mar 29, 2010)

ksouers  said:
			
		

> Dave,
> I would suspect you don't really want to machine it. Will drilling the rod deep enough to bury the magnet suffice? You could then fair the surface with thickened epoxy.



Maybe mix the epoxy with some cast iron swarf?


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## Blogwitch (Mar 29, 2010)

Dave,

I think everyone has got it spot on, except that grinding can usually be used on weird and wonderful materials. Marv mentioned rubber, well that can be ground with ease to very close limits.

Get yourself a toolpost grinder (or even a dremel), fix it onto a ball turner, and away you go.


Bogs


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## grg12 (Mar 29, 2010)

Hallo

Without thier protective coating they will oxidize and loose thier strength. It wont happen within hours but after some weeks or maybe months your magnets will be junk.
Gregor


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## Noitoen (Mar 29, 2010)

If you can't use a little extra thickness by adding a machined piece of steel to fill the gap, get a thiner magnet and make up the thickness with the steel part and epoxy it in place. The energy loss wont be so great.


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## doc1955 (Mar 29, 2010)

Here are some machinable magnets.
http://www.mcmaster.com/#rare-earth-magnets/=6fleif
And yes they are neodymium.
We have done this at the shop where I work with great success.
So I say give it a try you do have to use carbide or grind.


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## mu38&Bg# (Mar 29, 2010)

Machining high strength magnets can be ugly. I was trimming a rotor for a brushless motor once and clipped a few magnets. There was a lot of sparking for just grazing them.

An option is to use a square magnet and add a steel pole piece that would be machined to shape.

If you ever need to shorten a magnet you can just break it. I did this by clamping the magnet in a grinding vise with end I wanted to remove sticking out past the jaw. A light tap with a firm object will usually result in a clean break.


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## Stan (Mar 29, 2010)

About ten years ago I made a 5" magnetic lathe chuck out of a 2" thick block of 6061 aluminum. I cut recesses in it with an end mill for about ten 3/4" super magnets. These were the shiny ones that look like large watch batteries. I epoxied the magnets into the recesses and then put the chuck on the lathe and faced the surface. The facing cut removed the shiny metal case and cut various amounts of the black magnetic material underneath.

I have always used flat washers as keepers on each magnet when not in use and they don't appear to have lost any strength. 

This just proves that when you don't know what you are doing and what material you are working with that sometimes it will work.


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## doc1955 (Mar 29, 2010)

I was thinking of doing a magnetic chuck myself I have machined these magnets with no problems but I did use carbide. 




			
				Stan  said:
			
		

> About ten years ago I made a 5" magnetic lathe chuck out of a 2" thick block of 6061 aluminum. I cut recesses in it with an end mill for about ten 3/4" super magnets. These were the shiny ones that look like large watch batteries. I epoxied the magnets into the recesses and then put the chuck on the lathe and faced the surface. The facing cut removed the shiny metal case and cut various amounts of the black magnetic material underneath.
> 
> I have always used flat washers as keepers on each magnet when not in use and they don't appear to have lost any strength.
> 
> This just proves that when you don't know what you are doing and what material you are working with that sometimes it will work.


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## deverett (Mar 29, 2010)

Thanks for all the replies. Plenty of food for thought there.

I think I'll go with either the filler pieces of steel as end caps or the cast iron dust filled epoxy method. I have to machine some castings in the near future, so will have a copious supply of dust available!

Dave
The Emerald Isle


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## Maryak (Mar 30, 2010)

mklotz  said:
			
		

> Maybe mix the epoxy with some cast iron swarf?



Or buy it pre mixed as liquid steel.

Best Regards
Bob


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## Quake (Mar 30, 2010)

Few things -

1) I have bought quite a lot of these from kjmagnetics.com - they can make them in custom shapes for you - don't know what the minimums might be

2) little known fact - in many scenarios, the magnets actually have MORE strength if they are sandwiched between steel plates, or even if they only have steel on one side. Check out KJ Magnetic's pull force calculator - http://www.kjmagnetics.com/calculator.asp - or if you are into Calculus, do some googling for Faraday's Law. Using a smaller magnet + a steel plate, depending on your use, could actually enhance the magnet's strength.

3) if you try machining them and notice they lost the magnetism, just give it a rest - unless you paid $$$ for the high-temp ones, they will start loosing their magnetism around 186*F - but when they cool, it will come back. (Unless you get them WAY too hot) This is why they are tricky to use in electric motors. (they are popular in DC brushless motors for RC aircraft - see www.gobrushless.com for more info - the air cooling makes them useful there.)

* not affiliated with kjmagnetics.com other than as a (happy) customer.


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## precisionmetal (Mar 31, 2010)

I've cut them in my wire edm machine with no problem.


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## deverett (Mar 31, 2010)

Maryak  said:
			
		

> Or buy it pre mixed as liquid steel.
> 
> Best Regards
> Bob



BUY? I didn't think swearing was permitted on sites like this.

I'll stick (if you'll excuse the pun) to mixing my own if I go that route.

Dave
The Emerald Isle


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## Maryak (Mar 31, 2010)

steamdave  said:
			
		

> BUY? I didn't think swearing was permitted on sites like this.
> Dave
> The Emerald Isle



Dave,

Forgive my lapse in concentration - 

Best Regards
Bob


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## tel (Mar 31, 2010)

Seems to me you'd 'ave to b... bu... b ... - you know, that 'b' word, the epoxy any'ow,(unless you blokes know something I don't) so you might as well get the filled stuff while the madness is upon you.


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## deverett (Apr 1, 2010)

tel  said:
			
		

> Seems to me you'd 'ave to b... bu... b ... - you know, that 'b' word, the epoxy any'ow,(unless you blokes know something I don't) so you might as well get the filled stuff while the madness is upon you.



I managed to PURLOIN some epoxy a while ago, so it will need using up before it goes out of date.


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## bearcar1 (Apr 1, 2010)

hmmm, PURLOIN ??? , don't you mean BORROW :big: :big: :big:

BC1
Jim


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## PhillyVa (Apr 1, 2010)

Dave,

I had an experience with a couple of rare earth magnets that where several inches apart. They came together and one shattered. It was real fun getting all the little bits off the one that was still good. (they where sharp little buggers).

I think like bogs, grinding may be the best option, but you'll have to deal with all the magnetic filings

Or check out "A" in this link

http://www.leevalley.com/wood/page.aspx?c=1&p=45088&cat=1,42363,42348&ap=2

Hope this helps,

Philly


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## deverett (Apr 2, 2010)

Philly

Thanks for the link.

I am presently at 'work' out in Saudi Arabia and have plenty of available time to occupy. During some of this time I dream up all sorts of projects for when I get home - few if any ever seem to materialise due to calls on my time from SWMBO.

One such scheme was to build a small generator. Somewhere I had seen plans for one that used a shaped alnico magnet as the pole pieces. I couldn't find any suitable alnico magnets, so then wondered about rare earth magnets - hence the initial query.

Dave
The Emerald Isle - well, one day.


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## dghibner63 (Nov 15, 2012)

I machine NdFeB every day.  You can grind it with a conventional or diamond wheel.  The conventional will wear more, but you might get lesss chipping.  You cannot remove too much stock at once.  Use a lot of coolant because the dust is combustible and there will be a lot of sparks.  The dust is NOT good for you.  You also must add some type of protective coating as mentioned by someone else, Neodymium breaks down quickly - no matter how you treat it.  A protective coating will slow the process - but make sure the magnet is completely dried before coating or you will end up with rusty junk very soon.  Neo rusts extremely fast - keep it dry when not machining.


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