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How Hot
- Thread starter U.C.O.K.
- Start date
If it starts to change colors, you've probably got issues. The technical answer would be anything higher than the final tempering temperature is too hot, but for that to mean anything, you have to know what the temperature was and have a way to measure what temperature you've reached.
Unless he has Chef's Hands, in which case the metal could be white hot and he'd think it was fine.
Jason B.
Knifemaker / Craftsman / Service Provider
- Joined
- Jun 13, 2007
- Messages
- 11,179
Some may argue but I beleive that if you see sparks too much heat is being created. Remember the edge is very small, not much is needed to ruin that. I've kept my blades plenty cool before, using wax on the belts, dipping the blade in cold water after every pass, worked good and the blade never got hot but the edge burr was still blue... so how hot did it really get? I'll stick to my slow stones.
Hi,
How hot is too hot? It depends on the steel. Most knife steels will lose some hardness if the heat generated during machining is more than you can touch. And yes, sharpening is a machining process. A few, like HSS and to a lesser extent, D2, (a hot work die steel), are able to hold their temper at much higher temps. HSS will hold it's edge and temper to a red heat. That's why it was developed to make cutting tools for lathes and mills. As a side note, T-series alloys will hold an edge and temper to 5000F to 6000F.
Keeping material cool during machining can be achieved several different ways. First, if you do the process slow enough, (rubbing your knife on a rock by hand), you won't create enough friction fast enough to build damaging heat. Things get a little more complicated when we switch to powered grinding. There are a couple things we can do to beat the heat. We can run a coolant to carry the heat away, either a fluid or air. But that tends to be messy at home. Or we can machine fast enough to have the heat carried off by the swarf. Those sparks that you see coming off your knife edge UCOK, are actually a good thing. That is where most of the heat is. But notice I said, MOST, but not all. Some heat is left behind. And with the very thin section that makes up a knife edge, there isn't a lot of mass to absorb much heat. And the tools generally available to home knife guys mostly can't remove stock fast enough to be totally "safe" to the edge to sharpen dry. In manufacturing, I would combine these two processes, coolant and high speed stock removal to give the edge every chance.
dalee
How hot is too hot? It depends on the steel. Most knife steels will lose some hardness if the heat generated during machining is more than you can touch. And yes, sharpening is a machining process. A few, like HSS and to a lesser extent, D2, (a hot work die steel), are able to hold their temper at much higher temps. HSS will hold it's edge and temper to a red heat. That's why it was developed to make cutting tools for lathes and mills. As a side note, T-series alloys will hold an edge and temper to 5000F to 6000F.
Keeping material cool during machining can be achieved several different ways. First, if you do the process slow enough, (rubbing your knife on a rock by hand), you won't create enough friction fast enough to build damaging heat. Things get a little more complicated when we switch to powered grinding. There are a couple things we can do to beat the heat. We can run a coolant to carry the heat away, either a fluid or air. But that tends to be messy at home. Or we can machine fast enough to have the heat carried off by the swarf. Those sparks that you see coming off your knife edge UCOK, are actually a good thing. That is where most of the heat is. But notice I said, MOST, but not all. Some heat is left behind. And with the very thin section that makes up a knife edge, there isn't a lot of mass to absorb much heat. And the tools generally available to home knife guys mostly can't remove stock fast enough to be totally "safe" to the edge to sharpen dry. In manufacturing, I would combine these two processes, coolant and high speed stock removal to give the edge every chance.
dalee
when i sharpen carbon steel knives on the abrasive wheel i notice some sparks but the blade is not being pressed hard and the sparks are very light. there is no color change and i havent felt temperature change. in this video i'm sharpening a knife i made and the sparks arent anything like they appear to be. http://www.youtube.com/watch?v=plMbnQMQJMg
Hi,
The thing is, a section as thin as a knife edge can cool as fast as it heats. Our fingers feel the heat behind the edge not right at the edge. The steel can literally be burnt right at the very edge and still feel only slightly warm to the touch. How much damage occurs depends on how far back into the blade the heat has traveled. It might be all the way though the blade, or just right at the very edge. But there is damage, it can't be helped.
A light or heavy touch will influence how much heat stays in the blade. Obviously, a heavy touch will create more friction and generally "choke" the cutting action allowing heat build up. But you might be surprised at how hard you can push different types of machining operations and not build up heat. But in abrasive machining for knife making, you can't push the work that hard. Belts and wheels tend to clog and stop cutting pretty easily. Should you as a knife maker toss out your grinders? No, the speed increase will out weigh the potential for damage. You just need to be careful.
dalee
The thing is, a section as thin as a knife edge can cool as fast as it heats. Our fingers feel the heat behind the edge not right at the edge. The steel can literally be burnt right at the very edge and still feel only slightly warm to the touch. How much damage occurs depends on how far back into the blade the heat has traveled. It might be all the way though the blade, or just right at the very edge. But there is damage, it can't be helped.
A light or heavy touch will influence how much heat stays in the blade. Obviously, a heavy touch will create more friction and generally "choke" the cutting action allowing heat build up. But you might be surprised at how hard you can push different types of machining operations and not build up heat. But in abrasive machining for knife making, you can't push the work that hard. Belts and wheels tend to clog and stop cutting pretty easily. Should you as a knife maker toss out your grinders? No, the speed increase will out weigh the potential for damage. You just need to be careful.
dalee
if he is using a regular grinding wheel then i wouldnt let him touch a knife. if its a lawnmower blade that wont matter a whole bunch but for a knife, i would rather do it by hand. a regular grinder can remove a lot of metal quickly and shorten the life of your knife
Absintheur
Banned
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- Jan 31, 2008
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- 3,280
Unless he has Chef's Hands, in which case the metal could be white hot and he'd think it was fine.
No...but he might think it was medium well done...lol.
