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magnatism and edges

H

Hu Lowery

Joined
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Roseland, LA
I can't remember if it is the grain of the metal or what that lines up when something is magnetized and is in random alignment when it isn't. Just wondering with the endless quest for the perfect edge, has anyone tried to determine if magnetizing a tool has any effect on tool sharpness or edge durability? Probably need a CBN wheel to minimize heat at the cutting edge and even the heat generated with one of those might be too much.

Hu
 
hu lowery said:
I can't remember if it is the grain of the metal or what that lines up when something is magnetized and is in random alignment when it isn't. Just wondering with the endless quest for the perfect edge, has anyone tried to determine if magnetizing a tool has any effect on tool sharpness or edge durability? Probably need a CBN wheel to minimize heat at the cutting edge and even the heat generated with one of those might be too much.

Hu
Click to expand...

The grain structure can't move in the solid phase. It is individual molecules of each micro grain particle that have a magnet polar structure. Magnetization causes the random orientation of these individual molecules to have an average increase in alignment along the magnetic force direction. The stronger the magnetizing force the greater number of molecules that line up along the magnetic force. When 100% of the molecules are lined up, then the material has reached magnetic saturation. When the external magnetic force is removed, some of the molecules stay oriented along the magnetized direction and some molecules only partially return to their former alignment. This is the residual magnetization of the material. As noted in previous posts there are several ways to remove the magnetization. The most effective is heating, but the others work well enough for most practical purposes. Striking does not always work if the magnetization is strong.

BTW, I think that super cooling down to cryogenic temperatures may also work to demagnetize the steel just in case anybody has a really good refrigerator. 😀
 
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I remember years ago reading (maybe in Fine Woodworking) that some of the old timers believed that hanging tools like bench chisels on a magnetic strip would cause the edges to dull. I believe most didn't agree.

robo hippy
 
If you rub the magnetized tool with a frog hair cloth, it will remove the magnetism, but the side effect is that it will cause warts to appear on the tool. 🙄

Warts on the cutting edge present a problem that is worse than magnetization.
 
"BTW, I think that super cooling down to cryogenic temperatures may also work to demagnetize the steel just in case anybody has a really good refrigerator. 😀[/QUOTE]"

Send them to Odie this week (per his gallery thread, it's -15 there). It's been near 0 for the last 2-3 weeks (except for a couple of days) with a few days in the -10 degrees. I am ready to shoot the groundhog!!! Gretch
 
If your heating the tool hot enough to change the magnetizm your grinding far too hard. Don't know about HSS or particle metal steel but you have to heat a carbon steel tool to red hot to make it non magnetic. you would have to really grind to get a tool red hot. So get out your frog hair and attack the tool. Actually I have a doll copy of your tool and have been poking needles in it to make it get dull quicker. 🙂
 
john lucas said:
If your heating the tool hot enough to change the magnetizm your grinding far too hard. Don't know about HSS or particle metal steel but you have to heat a carbon steel tool to red hot to make it non magnetic. you would have to really grind to get a tool red hot. So get out your frog hair and attack the tool. Actually I have a doll copy of your tool and have been poking needles in it to make it get dull quicker. 🙂
Click to expand...

The heating that was discussed above isn't from grinding, it is from putting it in a 350° F oven for ten minutes -- see Hu's post.
 
Bill Boehme said:
If you rub the magnetized tool with a frog hair cloth, it will remove the magnetism, but the side effect is that it will cause warts to appear on the tool. 🙄

Warts on the cutting edge present a problem that is worse than magnetization.
Click to expand...

OK, that was funny, warts and all
 
a somewhat serious question

john lucas said:
If your heating the tool hot enough to change the magnetizm your grinding far too hard. Don't know about HSS or particle metal steel but you have to heat a carbon steel tool to red hot to make it non magnetic. you would have to really grind to get a tool red hot. So get out your frog hair and attack the tool. Actually I have a doll copy of your tool and have been poking needles in it to make it get dull quicker. 🙂
Click to expand...


John,

While I don't think magnetized or nonmagnetized would make any real world difference the question was I think valid. All this heating and freezing and such, particularly the freezing, is of debatable value but it seems to be more and more widely accepted that freezing anything is of benefit. I do have to admit it is of great benefit to ice cream, other things I'm not so sure. I can say with 100% certainty I have never found freezing to be of benefit to me!

Since we are talking about the very cutting edge itself I have to assume that it reaches the same heat as the pieces that are sheared or torn off of it that we see as sparks or very close to the same temperature. It might only hit that temperature for a moment in a tiny area but that is the area we would be cutting with.

I am sometimes guilty of overheating a tool when first shaping something but by and large I don't and resharpening never creates noticeable heat with the soft white wheel I use. My training was on far older alloys than this newfangled stuff and if you ever made it change color you had destroyed the temper even if you ground or polished the surface to hide the evidence. A lot like sharpening before the tool is dull, I was trained to cool before the steel was hot. I think we may have the most ability to learn as teenagers even if often the least willingness. I remember the things taught then and have forgotten a million and one things learned since then.

Hu
 
It's the high vanadium content of CPM-10V steel that mainly accounts for its properties. Thompson lathe tools use a tripe tempering process that converts the austenite to martensite which is the process that created the carbides that give the steel its hardness and makes it wear resistant. They follow the first high temperature tempering cycle with a cryogenic cycle which is said to further increase the conversion to martensite. I suspect that the difference between the same steel with a cryo tempering cycle and steel that doesn't include it would not be noticeable to woodturners.
 
That's finer than Frogs Fur!

Well, I ain't ever seen fur on a frog.

Well, that is because it is so fine.

I think that came via my grandpa, many years ago in Missery, or Missura as he and grandma used to say....

Any way, I have noticed that my chisels become magnetized when I sharpen them. Lay them down next to the grinder, and they come up with a metal filing beard. A light tap on another steel seems to demagnetize it. At least all the beard comes off.

robo hippy
 
Bill Boehme said:
Thompson lathe tools use a tripe tempering process....
Click to expand...

Funny - Doug has never mentioned cow stomach as part of his toolmaking process... 😉

(I guess you "got the 'L' out of there" Bill??)

R. 😀
 
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