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spope14
02-21-2002, 07:52 PM
New challenge from a student. he wants to make a magnet. The idea came after he had surface ground a set of hardened parallels (4150), and found them to be magnetic. His father or brother or something said to him "Hey, why don't you make a magnet that can haul about five pounds for me. I need one to put on a rope to get tools out of the river when I am working". He works on or under bridges, thus the river and such.

OK, so I could say - "hey for probably five to eight skins, you can buy a magnet", but alas, I really do NOT want to kill the adventuresome spirit of learning - and he is watching me type this and will be checking in on this board.

Seems I remember something like beating a piece of steel with extreme predjudice (I really love that term, the student is looking over my shoulder puzzled about what that means) with a hammer will do it, but I need some better ways, info, and such.

OK you machine shop experts, help me out here.

SGW
02-21-2002, 09:10 PM
Put the steel in a strong DC electromagnetic field and suddenly turn off the current.

Some kinds of steel will work better than others, too, but that sounds like a good research project for the student....

JimWolford
02-21-2002, 10:17 PM
Magnets used to be made with a hammer-MANY years ago.
Goes like this, first determine magnetic North at your position.
take a bar of SOFT IRON, steel don't work as well, and heat it to red in your forge.
Lay the iron bar on the anvil so that it points towards the magnetic North pole.
Pound the iron untill it is cool, at this time you will find by checking that you have made a magnet.

It,s how the first compass needles were made about 500 years ago ;-)

Jim

Thrud
02-21-2002, 10:21 PM
The strongest permanent magnets known to man are NbFeB (it was accidentally discovered after a nuclear bomb test - or so I have been told). A piece 1/8" diameter can easily pick up a 5lb. block of steel. You can salvage these rare earth magnets out of dead 3 1/2" hard drives as they are used in the linear motor accutators (voice coil drive) for the r/w heads. Lee Valley Tools sells coin shaped, rods, washers, half spheres and spherical NbFeB PM magnets.

Making your own is a waste of effort. A coil of wire on a soft iron core makes a good electromagnet Hammering does magnetize as does placing magentic materials in a strong magnetic field - non-alternating, of course - an AC field can actually degauss a magnet. The piece he had was magnetic because it was held on a magnetic chuck for grinding - you normally degauss pieces after being held in magnetic chucks.

dave

Oso
02-21-2002, 11:20 PM
If yer gonna make a magnet, soft iron does NOT work, as it won't hold the magnetic "charge". Steels DO. Compensators on old Navy compasses are soft iron because they don't hold the magnetism (low remanent field)

You can point a piece of rod north and hit it (uses earth's magnetic field)

heat it and let cool in a field, such as pointing north.

Hit it with a LARGE external field, like a magneto charger applies.

There are likely other ways, the idea is to get all the little "magnetic domains" lined up in the same direction. REmanent magneism is the degree to which the domains stay that way after the field is removed.

The 5 lb is a problem, takes a good magnet material, most of those are already magnetized!!!!! :-)

snorman
02-22-2002, 01:08 AM
I don't think it's practical to try to make a magnet. Lot of work and it won't be worth a hoot. If you want a really good magnet tool, I suggest using a cobalt magnet. They hold their magnetism much better than other types and they're stronger than most. You might try Edmund Scientific. I don't recommend neos.

lynnl
02-22-2002, 11:24 AM
I was unaware of the process of heating to red heat and pounding while aligned w/magnetic N to introduce permanent magnetism. As a youth I recall magnetizing some screwdrivers by coiling a wire around them and jumping the wire across Dad's car battery. Produced some pretty sparks, as well as magnetic screwdrivers. My question is: would that process have been enhanced by heating the screwdrivers? ... would they have to be heated to critical temp?

willjordan
02-22-2002, 03:02 PM
I was told once that many shipways are aligned so that the keel is east-west (magnetic?) to lessen the tendencey for a vessel to carry its own magnetic field. I imagine that this may have been the case in the days of rivited hulls. Not so certain if it makes so much difference with a welded hull.

------------------
grace & peace
will

[This message has been edited by willjordan (edited 02-22-2002).]

hms50
02-22-2002, 08:17 PM
Hi Scope,

As a fellow teacher I read your note with interest. At my school we have a magnet charger that the physics teacher has the kids make magnets with. We found that o1 will work pretty well as will w2. The charger consists of two soft iron pins about 3/4 inch dia. Each pin is wound with hundreds of turns of copper magnet wire. One coil is wound clockwise, the other counter clockwise so they will create opposite poles. A car battery will supply the d.c. current needed. When I was a kid, a fellow showed me one of these he made to recharge magneto magnets with. Before alnico, this was a constant problem. He used 120 volt a.c. because it was handy! Don't try this with kids around! He used a piece of aluminum foil in the circuit. The foil would burn out so fast that the magnet would be charged before the electrons changed directions! In other words, the circuit only lasted for 1/2 of one cycle. This method didn't work every time, several trys were somtimes needeed. I think Lindsay has a book with plans for a magnet charger in it.
Good luck
hms50

snorman
02-23-2002, 08:50 PM
Here's a schematic for a mag zapper for slot car motors if you insist on making your own.

http://www.oldweirdherald.com/techtips/magzap.jpg

These things store a charge and release it all at once and are potentially lethal so use caution anytime you are handling them.

Oso
02-23-2002, 09:24 PM
I looked at that, and without seeing any explanations, I am dubious.

Most pulse zappers do NOT have any sort of core in them. The core tends to increase the inductance to the point that the pulse is stretched out and the peak lowered. The peak does the work.

I have seen zappers that charge an 18" speaker magnet, WITH THE FULL MAGNET STRUCTURE IN PLACE ("shorting" the magnet). No core.
Speaker weighs about 30 lb or more, it jumps when the pulse hits it.

RPease
02-23-2002, 09:49 PM
Spope14,

If you are interested, there is a quick little tutorial on magnets at http://www.slick7.com/

Once there, click on "Tech Articles" (on left side of page) and then select "Maget Manual" (their spelling......not mine).

Might be of interest to the student.

Doesn't mention anything about the "east-west" hull orientation thing. Never heard of that before, but there are lots of things that I've never heard of. (And lots we "puny humans" don't have any idea about.) Sounds interesting though. Maybe that's why I keep getting lost on the lake in my boat. Hull must have been built in the wrong direction.

Regards,
Rodger