Magnetic blade

L

Lanza

Joined
Oct 29, 2005
Messages
1,022
I just discovered an unused hunting knife I've had for awhile has a magnetic blade. Any thoughts on what this means would be appreciated.
 
That perhaps it was lying in a toolbox next to a magnet for all those years..?
 
Stop by any machine shop and ask them to de-magnetize it for you. Only takes a second and they probably wont even charge you.
 
Just whack it on the edge of a table or vise. It will no longer be magnetized.
 
Maybe you could use it to remove steel shot from your pheasants and ducks that you shoot ;-)
 
Ordinarily, I'd have no clue as to why (or how) a knife blade might become magnetized without deliberate effort to make it so. But oddly enough, I was experimenting with convex sharpening a few days ago, using sandpaper on a rubber sanding block. The knife I was sharpening is called a 'duct knife' (double edged, dagger-like utility knife) that I purchased at Home Depot a while back. Apparently these are used by installers of heating & A/C system ductwork. Anyway, I was dry sanding the blade, and I noticed afterwards that the metal filings were clinging to the tip of the blade, just as they would to a magnet. So far as I know, the knife wasn't magnetized prior to sharpening. It'd just been laying on a table for a while.

I've been reading online a bit about magnetism, and apparently it's possible to magnetize some materials with 'vibration', if the material happens to be aligned with the earth's magnetic field while the vibration is taking place. Perhaps the vibration of sanding/sharpening induced some magentism into the blade steel? I'm not sure, but it makes me wonder...
 
When heated above a certain point ferromagnetic materials tend to pick up even small magnetic field and once cooled while in that magnetic field tend to be magnetized. It's very common in knives since they are heat treated at high temps. Especially in knives that are induction heat treated and made in factories that may have magnetic fields due to high power wires near furnaces. Especially if it's an electric furnace.
 
Obsessed with Edges said:
Ordinarily, I'd have no clue as to why (or how) a knife blade might become magnetized without deliberate effort to make it so. But oddly enough, I was experimenting with convex sharpening a few days ago, using sandpaper on a rubber sanding block. The knife I was sharpening is called a 'duct knife' (double edged, dagger-like utility knife) that I purchased at Home Depot a while back. Apparently these are used by installers of heating & A/C system ductwork. Anyway, I was dry sanding the blade, and I noticed afterwards that the metal filings were clinging to the tip of the blade, just as they would to a magnet. So far as I know, the knife wasn't magnetized prior to sharpening. It'd just been laying on a table for a while.

I've been reading online a bit about magnetism, and apparently it's possible to magnetize some materials with 'vibration', if the material happens to be aligned with the earth's magnetic field while the vibration is taking place. Perhaps the vibration of sanding/sharpening induced some magentism into the blade steel? I'm not sure, but it makes me wonder...
Click to expand...
Slightly off-topic: I have one of those HD duct knives, I sharpened it up but have not used it yet. What is your opinion of the blade steel on yours? Mine felt like 440A when sharpening. It is not magnetized.
 
Bill1170 said:
Slightly off-topic: I have one of those HD duct knives, I sharpened it up but have not used it yet. What is your opinion of the blade steel on yours? Mine felt like 440A when sharpening. It is not magnetized.
Click to expand...

I'm assuming whatever steel it actually is, it's nothing special. 440A might be a little too generous assumption of it. I have an older Kershaw Leek made with 440A, and I think even that is likely better than whatever this duct knife is made from. It seemed to be VERY easy to remove metal from this blade (I was also a bit surprised by the quantity of filings coming off of it when sanding). This knife was a cheap one, and I'm assuming the steel is probably Chinese or otherwise 'imported' from who-knows-where. I used the knife to cut some pink fiberglass insulation, and the edge didn't seem to hold up to that very long beyond the first couple of cuts. But then, that's basically what I expected of it when I bought it (for around 7 or 8 bucks, I think).
 
If you stick the blade through a soldering gun's loop (it has to be the kind with the loop), it will be demagnetized.

My D4 got magnetized when I was flat-grinding the blade using a belt sander. I guess all the static buildup did something to affect the magnetic polarity of the blade, and the blade's magnetic field was pretty strong. Like I said, the soldering gun took care of that right away.

Bill DeShivs said:
Just whack it on the edge of a table or vise. It will no longer be magnetized.
Click to expand...

This never works, at least not for me. Maybe if you whack it hard enough to break it.
 
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