Author Topic: Cutting Magnets (Read 8336 times)

taylorp035 · « **on:** August 05, 2009, 04:56:19 PM »

Today I tried to cut a 4 pole hard drive magnet in half to make two separate magnets using a hacksaw. The result was a half decent magnet and a bunch of little broken pieces. After getting halfway through, it kind of crumbled into several pieces. Also there was a lot of sparks and I was concerned that something may be toxic. Any suggestions?

Flux · « **Reply #1 on:** August 05, 2009, 12:06:13 PM »

Most hard drive magnets are actually two blocks of neo on a steel backing plate, Not sure which ones you have.

There is a fair bit of data on separating the neo from the backing plate on the site and this doesn't involve cutting the neo.

Cutting neo is dodgy and I wouldn't really encourage it. I have cut them wet with a diamond tile say perfectly satisfactorily. I wouldn't try it dry as the dust is certain to be toxic and the stuff is not far removed from lighter flint and the dust will probably self ignite. If you cut them wet dispose of the slurry carefully. I don't think neo is a great problem but samarium cobalt dust is very dodgy when it dries out.

Flux

taylorp035 · « **Reply #2 on:** August 05, 2009, 12:36:35 PM »

Thanks Flux,

My magnets are one solid piece, not two separate magnets. I have been successor at removing the backing plate since there is very little glue holding the magnet down.

I also noticed the filings catching on fire.

The reason on why I am cutting the magnets is to use them in a car alternator conversion. I have already prepared the rotor and removed the internal wire. My goal with the project was to hit 12volts at a reasonable rpm ( <500 ). The bearings in the alternator are very nice and beefy needle bearings.

taylorp035 · « **Reply #3 on:** August 05, 2009, 12:41:23 PM »

Do you guys think that I could "score" one side of the magnet and then snap it in half?

ghurd · « **Reply #4 on:** August 05, 2009, 01:02:21 PM »

I score them on both sides, with a utility knife.

Deep as you can in one or 2 passes. It does not take much depth.

I hold one side in pliers very close to the score, the snap it in 2.

It doesn't always work like I hope.

But is a lot faster. Costs less for saw blades too.

Be sure they are 2 poles per side before cutting.

If there are 2 separate magnets next to each other, they do not need cut.

'Snapped' would be a better word and procedure than 'cut'.

G-

FishbonzWV · « **Reply #5 on:** August 05, 2009, 02:29:16 PM »

I depends on how thick the mags are.

I cut some old Maxtor SCSI's, (1/4" thick) with a hand grinder and a cutoff wheel.

I stuck them on my vice and quickly scored each side. Then snapped them in half.

The latest ones are only 1/16" thick, easily broken and easy to snap.

Bonz

taylorp035 · « **Reply #6 on:** August 05, 2009, 03:22:17 PM »

My first magnets are 1/8" thick and 3/4" wide roughly and 1.5" long. My other set is 1/4" thick and 1/2" wide.

tanner0441 · « **Reply #7 on:** August 05, 2009, 03:44:23 PM »

Hi

I have tried cutting these with mixed success, a submeged diamond cut off disc seems most reliable. I used to cut ceramic scanning coil cores with high frequency high voltage AC. Score them with a diamond scribe then pass the current along the score line. I doubt you will score a neo magnet with a craft knife. Also most of the dust finishes up stuck to the magnets.

I removed then magnets from the steel backing by warming the backing and shearing the magnets off.

Brian

Flux · « **Reply #8 on:** August 05, 2009, 03:47:59 PM »

At 1/8 thick you can probably nick them both sides with an angle grinder and snap them it will save a lot of cutting. Beyond 1/4" thick the snapping may be too unpredictable and you would need to cut them through.

I am sorry to disappoint you but unless you have altered the winding you will not reduce the cut in speed with neos. The standard wound rotor is capable of saturating the alternator core so if it need over 1000rpm with the standard rotor you won't get better with neo. All you will do is remove the need to supply something like 40W to the field before you get output but you won't cut in at a lower speed.

Flux

taylorp035 · « **Reply #9 on:** August 05, 2009, 04:06:52 PM »

I just tried to score one of the magnets and it didn't cut at all. I then proceeded to snap the magnet in a wood vice, and all that did was make a bunch of really small pieces.

Also thanks flux for the saturation advice. One reason on why I am trying to do this project is because the brushes / contactor is broken and does not work.

I have 2 more 1/8" magnets, any more suggestions for these? I could try to carefully hacksaw again, maybe on the face for a better cut. I am 1 for 4 so far and the "1" isn't very good.

ghurd · « **Reply #10 on:** August 05, 2009, 04:22:50 PM »

I have cut many 100s, possibly 1000s, of HD neos by scoring them with a utility knife.

Removing them from the backing plate is as simple as slowly bending the backing plate back away from the neos.

Neither works every time, but I am only willing to spend so much time and money on 15 cents worth of magnet.

G-

taylorp035 · « **Reply #11 on:** August 05, 2009, 05:40:40 PM »

That's nice, but my budget is elbow grease.

I will try number 3 after dinner.

taylorp035 · « **Reply #12 on:** August 05, 2009, 06:32:25 PM »

Therefore, do you think I should re-wrap the field coils with the thinner rotor coils?

taylorp035 · « **Reply #13 on:** August 05, 2009, 07:40:12 PM »

Also, the wire that I have is 18 gauge and about 400ft of it.

Flux · « **Reply #14 on:** August 06, 2009, 12:13:58 AM »

Not sure what is available where you live. here in the UK we can get blades coated with tungsten carbide or something similar that are hard enough to cut hardened steel they would probably cut neo or at least notch it deep enough to break it.

Any grinder should notch it deep enough to get a reasonable break. I am not sure about normal hacksaw blades, I have never tried but they would probably struggle with the nickel coating even if they managed the neo.

Many hard materials can be cut with a soft blade ( back side of a cheap hacksaw blade may be better) and silicon carbide powder and plenty of water. Diamond powder is even better. Just seems too much effort for a low cost project.

Replacing the field coils will get you a working alternator again but it won't work at low speed. To lower the speed you need to rewind the stator. For wind the end result will hardly be worth the effort but give it a try, it will be fun, and cheaper than buying one of the many rewound pmg based car alternator things from various websites that claim they are marvellous.

Flux

trader dutch · « **Reply #15 on:** August 07, 2009, 05:49:28 AM »

Short sweet and simple , Tile nippers. Some nippers may have a spacer opposite the hinge of the blades that you can file down to close the jaws tighter. The nippers with off set all ways well need the jaw closure modified but will snap cut the entire H/D mag where the nippers looking like nail biters catch 2/3 of the H/D mag. Nail bitters work well to. A real large good nail biter will easily shear the H/D from the backer steel as well. No heat /no loss on the mag. Fast

taylorp035 · « **Reply #16 on:** August 08, 2009, 06:36:52 PM »

That's an interesting idea. I have a pair that has handles about 16 inches long and can cut through heavy steel wire with ease. I have somewhat given up on this idea of splitting the magnets, but I may come back to it in the future.

Thanks everyone for the suggestions!

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