Magnetism - Pros and cons.

[Kaizer]

Dear All,



Actually there are two questions buried in this post.



A] Have any of you great folks sharpened your SE / PE blades and then experienced that the blade becomes mildly magnetic?



B] If yes, then is it good? Bad?



I got one of my folders (a cheapo switchblade) which proudly says "STAAINLESS STEEL" and after due sharpening (Plain edged blade...get it sharpened on amotorized stone) promptly becames magnetised. I accedentally noticed themagnetis when a button compass i brought the knife near went awry and spun wildly. The blade geometry is a spear point with a "soft" steel.



HAvent sharpened my Big Ss that is the Spydercos as yet.



just wanted to understand the pros and cons of this if it does happen to my spydercos.



HAve a great day!



A door half open is a door half closed. But a knife half open is a knife fully closed.

[4 s ter]

Kaizer

The needle of the compass is a magnet with a N and S pole. Bring it close to any metal object and it will move. This does not indicate that the object is magnetized, only that the compass needle is.

If your blade will pick up (or move) small metal objects it is magnetized. Try small nails or something similar.

Regardless of the above, often when sharpening I have noticed the small metal particles cling to the edge of the blade and have to be wiped off. Likely some slight induced magnetism or static attraction.

David

"Not all who wander are lost"

[java]

Kaizer,

4 s ter’s answer is probably the most logical - that of ferrous material interrupting the earth’s lines of magnetic flux. This is the basis of how magnetometers and inertial navigation systems work. (And was probably the inspiration for Dr. Emmett Brown’s flux capacitor) However, if you start attracting nails and your knife sticks to the fridge after sharpening maybe this explanation will work….

Magnetism is still not fully understood but there are three elements: - iron, nickel, and cobalt – that display the phenomenon called ferromagnetism. This is why steel, being alloyed iron, is also commonly used for magnets. Ferromagnetic materials are composed of a large number of small volumes called domains and due to their inherent properties, they can be “magnetized” to the point of saturation by the presence of a strong magnetic, electromagnetic, and a few other forces. The ability to resist the decay of the magnetism once an inducing force is removed is called remanence and is affected by things like heat.

You said the knife has a soft steel. I’m not sure where the breakpoint that determines whether steel can be made into a magnet lies as far as the carbon to iron ratio goes but I am aware that strain can induce what is known as magnetic anisotrophy. The magnetism then tends to align itself in accordance with or perpendicular to the direction of the built in strain. The carbon in the steel causes the precipitation of iron carbide in the iron that form what is known as a second phase. The phase boundaries between the precipitate particles and the host iron form obstacles to domain wall movement and raises the coercive force and remanence compared to pure iron. Now I don’t know how soft the steel is, what the sharpening materials magnetic fields are, or if you are sharpening briskly and hard enough to induce a strain sufficient to magnetize the knife but, hey, it sounds like a good theory. Is it good? Seems an cool curiosity and a good coversation piece but I haven't a clue on the lasting effects to the blade.

Kaizer, your observation is interesting and made me delve deep within the ancient recesses of this rusty cranium to try and remember my basic inertial nav and magnetic flux theories. Surprised how much garbage is lodged under the old thinking cap. If anyone is interested, I can do an OT on another theory of how IN systems work but right now my brain is in pain so I’ll sign off early for the night.

In C8H10N4O2 and now a triple dose of 2,(p-isobutylphenyl) propionic acid, I remain,

java


Hmmmmm. My reference to INS was in error and was caught by a sharp mystery person at Boeing. It has been awhile and I should have said AHRS as in Attitude Heading Reference System. <b>These</b> systems commonly use a flux valve or a magnetoressistive sensor to measure variations in the earth's magnetic field (Usually 0.5 - 0.6 Gaus) to navigate. INS works by using 3 axis gyro assemblies or ring laser gyros to calculate acceleration errors from where it was to figure out where it should be (or where it isn't) and to get to where it should be.


Edited by - java on 5/3/2003 5:22:53 AM

[Sword and Shield]

I have an Old Timer that does the same thing. Sharpen it up, and it'll pick up paperclips or a finish nail. Use it a few times, and it's gone. Sounds like an induced magnetic field to me.

Well, it's nearly bug season here. Let the N,N-diethyltoluamide flow! <img src="smile.gif" width=15 height=15 align=middle border=0>

Never underestimate the impossible.

[sc_rebel1957]

Can't beat Java's explination of why, all I can add is I've ran into a couple of knives that had a very strong magnetism, both were B/Ms a Stryker and a Osborne.
I have no clue how they got that way and I doubt very seriously that it would hurt anything unless you were disarming land mines.
BUT! it so annoyed me that i traded both knives away promptly.
I use mostly diamond hones by DMT and the steel sticking to the metal part drove me nuts. Ron

[java]

Resplendent One,

Don't be a drinkin' thet stuff unless yer tryin' ta OFF yourself! Talk about WMD! Now go load me up another of your dimethylamine compound concoctions yer famous for. And don't scrimp on the 10-(3-dimethylaminopropyl)-2-chlorphenothiazine this time!! <img src="smile.gif" width=15 height=15 align=middle border=0>

Looks like I may have to look into the magnetism phenom a little more. Verrrrrry interesting....




&lt;font color=&quot;BLUE&quot;&gt;&quot;A hole-less knife is soul-less knife is a whole less knife&quot; - Javanese proverb&quot; &lt;/font&gt;

Edited by - java on 4/30/2003 7:32:20 AM

[Zrexxer]

It's been over 20 years since my materials science course, but I seem to remember that there are magnetic and non-magnetic stainless steels. The Austenitic steels are non magnetic, but can only be hardened by work-hardening and are not suitable for cutting edges. They have very high corrosion resistance though. Martensitic steels are magnetic, and can be conventionall hardened for cutlery uses. The bottom line of all this of course, is that knife steels can generally be magnetized.

Dan

[J Smith]

I know if you beat steel with a hammer it will aline the steel molacules and this is where the mag.comes from.I would think that the same thing will happen to a lesser degree when you sharpen steel.

I learn something new everyday,even though I don't want to. Jeff

[Sword and Shield]

OK, Java. Got a new tranq I've been working on for a while, it's called the Revolver. Six shots of Jamaican Blue, mixed with an equal amount thorazine. It'll stand you up before it knocks you out! <img src="smile.gif" width=15 height=15 align=middle border=0>

By the time you read this, you'll have already read it.

[java]

Resplendent One,

Wheelguns! Coooooool! Where's Revolvergeek when you need him?? Like the new sig. Reminds of the old saying, &quot;If I had a dollar for every dollar I spent, I'd have all my money back!&quot;

&lt;font color=&quot;BLUE&quot;&gt;&quot;A hole-less knife is soul-less knife is a whole less knife&quot; - Javanese proverb&quot; &lt;/font&gt;

Edited by - java on 4/30/2003 6:25:24 PM

[midget]

I like having my blades magnetized. It's useful for picking up crap every so often, like a needle or a tiny nail that you can't get your fingernail under.

I take a coil of wire, place my blade in the middle, and connect the ends to a battery, like a lawnmower, or motorcycle battery. Yes, i know, it shorts it, so i only do it for a sec or so.

You can't put your knife on the TV or your moniter, however, cause that will damage the screen.

I've never had a problem, and it's useful once in a blue moon.

[delicrazy]

i was gonna go into a speech about ions, but does it matter?
cons, you cant dig up land mines with them (like travolta did in that movie)
you cant rub your computer with them
you cant fly on maglev trains with it
youll end up like me and go in a circle for an hour and a half during your boyscout orientering course
pros
you can impress your friends and family.
the party gets boring, whip out the magnetic knife!
you can have someone you dont like dig up land mines.
erase peoples computers
rub them on cassete tapes to make them sound funny when played.
pretend your magneto
you can rob canadian people! (no offense VW but canadian coins are magnetic)
i think that about sums it up

[Kaizer]

Hi All!

Thanks for all your most valuable inputs. I got the drift about the alignment of the molecules. I think the heat generated while sharpening on the spinning wheel (it gets quite hot; there is a definate &quot;sting&quot; in the blade.. certainly not warm... but HOT)tends to do the trick of realigning the molecules.
My theory goes thus...
More heat = More kinetic energy in them atoms / molecules.
Now, a minimum amount of energy is used to keep the crystalline structure of the steel intact. The earths magnetic field then comes along and kind of &quot;casts&quot; them atoms into a north south (or south north?) orientation. And we have magnetism.
Java: Domo Arigato. The explaination shed some light on things i didn't know.
Thanks to all for their inputs.

This seriously is home!

Kaizer


A door half open is a door half closed. But a knife half open is a knife fully closed.

[sc_rebel1957]

Another useful tid bit of jibberish while I'm bored watching the clock <img src="wink.gif" width=15 height=15 align=middle border=0> if you're ever stranded in the Alaskan bush like in the movie the EDGE ya won't hafta be a wearin silk undies to make a compass <img src="smile.gif" width=15 height=15 align=middle border=0> Ron

[Sword and Shield]

Precisely, Kaizer! <img src="smile.gif" width=15 height=15 align=middle border=0> Actually the Earth's magnetic field is semi-backwards. When you think you are going North, you actually are going towards the magnetic SOUTH pole and vice-versa.

Think about it. North attracts South, right?

By the time you read this, you'll have already read it.