Sharpening question-should soarks fly?

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fatcat55

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Jan 1, 2010
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Someone please educate me...

At the gun show yesterday, I saw a guy sharpening knives. He was using a grinding wheel and sparks were flying from the fixed blade he was working on.

Forgive my ignorance, but seems like I have read that grinding wheels and excessive heat will ruin the steel. Am I missing something ? It seems like sparks just couldn't be good for most blades. No idea what brand but it was a finished knife.

Thanks for any information.

P.S. Saw another guy with a sign that said "FREE knife sharpening" and also a sign by the knives he had for sale that said "Most knives $5.00"...I guess you get what you pay for... I passed on his free offer figuring he probably "sharpened" those $5 knives!
 
are you sure he was not using paper wheels? with a carbon steel blade you will get some sparks which is normal when you sharpen with the grit wheel. the paper wheels will not ruin a blade when used properly like some guys (who dont know what they are talking about) will say.

i have sharpened with the paper wheels for 20 years and i'll never go back to anything else. check out the thread i started on them.
http://www.bladeforums.com/forums/showthread.php?t=578787

i couldnt resist asking you this question, what are soarks :p :D.
 
thanks for the information. That might explain what he was doing. Maybe I should have stopped to ask him and possibly learn something.

"Soarks" are the result of failing to proofread posts...

I find them very "commmon" in my posts.lol.
 
Depends on how much sparks you see and how long it takes for him to run the blade through. I typically get some sparks when sharpening carbon steels on my low grit belts, but those are far and few in between. A low grit grinding wheel that sends up a whole shower of sparks that goes all the way to the floor will probably ruin the temper within seconds. Though in some cases, you can ruin the temper even if you don't see any sparks if the guy spends over 5 seconds sharpening the same half inch of the blade.
 
Sparks will never fly from my knives. Heat removes the temper. If a steel molecule becomes red hot and flies from the blade, the molecules that were beside it were heated to the almost exact same temperature. One thing's for sure, throwing sparks from a blade definitely CAN'T be good for it.

Just my opinion. YMMV.
 
Sparks are always going to fly when applying steel (most steels) to a grinding wheel. The amount of pressure and the length of time you hold the metal to the wheel will determine how hot it gets. I've never used a grinding wheel on my knives, but have on many other things, and I use light pressure and keep the metal constantly moving. I also frequently quench the metal to cool it.

I'm no metallurgist, this is just based on experience :D
 
I've been sharpening and reprofiling with a belt sander for years, and have never ruined a temper past the first couple of weeks when I was learning on cheap machetes. Using new belts, the correct grit (if you need to remove lots of material, use heavy grits, don't just saw on it with a fine belt) and keeping a pail of water handy to dunk the blade in between passes will keep your temperature down just fine. I don't let any part of the blade linger on a moving belt for longer than a second or two, and even less if it's a very thin cross section to the blade which can't sink the heat as effectively. The hardest part of this of course, is to be able to return to the correct angle once you've pulled away from the belt and dunked the blade in water, but that just comes with practice.

Short version---if somebody who doesn't know what they're doing is using a power tool to sharpen, yes they can quickly ruin the temper. Making blanket statements like "if there are sparks flying then you've ruined the temper" as some have is a sure sign of not knowing what they're doing. I never finish an edge on a belt, the final bevel is always flattened on a stone, but I can get a completely dull/damaged knife to 95% of where it needs to be inside of a few minutes.
 
Most custom knife makers sharpen on belt sanders, and sparks do indeed fly when sharpening. It only ruins the heat treat/temper if you burn the steel by holding the steel in one spot, or letting the blade get hot while removing lots of metal.

Pay special attention to tips as thinner the steel, the easier it is to burn. Just keep the steel cool to the touch, dunk as necessary to keep it cool.

Same applies to paper wheels.

I have seen people use actual stone grinders at high speed to sharpen and I would not recommend it. Removes a lot of metal!


On a side note, I would probably bet that the knives for sale were not $5. I would suggest that that is what the sharpener charged for most knives to sharpen them for the customer!
 
glenns1956, the paper wheels are a lot different than a grinding wheel. i get the knives i make extremely sharp and i have no problem with the edges on them. if i did damage the edges, they would not hold up the way they do. check out the vid in this post. http://www.bladeforums.com/forums/t...-that-factory-edge-!!!!?p=9313785#post9313785

it takes a lot more heat than what you think to ruin the edge of a knife.

here is another vid of the same knife in the above vid cutting free hanging newspaper http://knifetests.com/kII.html
 
learned how to sharpen tool steel bits for turning down metal on a lathe way back in HS. i dont use this method on knife sharpening but i have to agree there would be sparks and that if done properly like its been stated , quenched often avoiding hot spots there should be no damage to the heat treat.
 
i took machine trades in school and i was amazed when i watched the teacher grind a tool bit for a lathe. when he quenched it the bit sizzled in the water. when he was done the bit cut really good. most steel used in making knives can take more heat than what most people realize.
 
richard j said:
i took machine trades in school and i was amazed when i watched the teacher grind a tool bit for a lathe. when he quenched it the bit sizzled in the water. when he was done the bit cut really good. most steel used in making knives can take more heat than what most people realize.
Click to expand...

Actually, I've seen a lot of tool steel being used in cutlery purposes. The bits I learned to grind were A2 steel, not sure what they were hardened too--probably not much considering they were going to be cutting metal.

But, yeah, we were taught basically not to let the edge get too hot to touch with our finger tips to avoid screwing up the temper. While trying to get the hang of this, you could tell really easily if you screwed up the temper because the steel at the edge would turn blue.
 
The sparking of the particles leaving the blade is not necessarily an indication of the temperature of the larger piece they came from. In other words, the red sparks leaving the blade do not indicate the blade they came from was the same temperature as the spark.

The other side of this is that metals that do not spark, like nickel and copper, can still be overheated by careless grinding.

Steel dust is somewhat pyrophoric, as I learned by asking this same question about 2 years ago. This means the tiny little particles of steel made by grinding will oxidize rapidly enough for them to get hot and glow.

On the sharpening side, there is research out there that indicates dry sharpening, even by hand, will produce temperatures at the very edge sufficient to soften steel tempered below 1000 degrees F.
 
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