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+--- Thread: Salutations to Stone Sharpeners! (/showthread.php?tid=217)
RE: Salutations to Stone Sharpeners! - grepper - 01-02-2018
Thanks Mr. Mark. Your post expresses many of my own thoughts regarding knife sharpening and the Internet.
For whatever reason, the sharpening world seems especially prone to birthing self proclaimed “experts” who freely, and even with apparent alacrity, spout out and represent as truth blatantly misguided, irrelevant, or at least ill-considered information, and the Internet offers the perfect venue to do it. It seems that now days all you have to do is sharpen one blade to become expert in the field and start spewing out “advice”.
So much of the sharpening information on the Internet is obviously endlessly repeated hearsay, and/or just opinion and folklore without any supporting data or even thoughtful theory offered as supporting evidence. But not all of it. There is also a lot of excellent useful information and expert advice. Your advice to use your best judgment is probably our best tool for ferreting out applicable and useful information. At least that’s what I do. Kind of like panning for gold. A lot of it is waste, but occasionally something pans out.
There is a real difference between spouting hearsay or opinion, and presenting for peer review a theory along with supporting data and evidence. The former is noise and blather; the latter is a quest for truth and a method of learning.
It is my hope, especially as the Exchange grows, that it remains a valued source of expertise, information, learning and research rather than devolving into yet another bloated bastion of babble. If everybody posts respectfully and thoughtfully it will surely come to pass.
We are lucky to have such an amazing and talented group of people here.
RE: Salutations to Stone Sharpeners! - me2 - 01-02-2018
(12-31-2017, 05:33 PM)grepper Wrote: Mr. Me2 – Because I sharpen on a Kally, I found a statement you made in post #31 of this thread interesting. You stated, “I have seen microhardness tests that show softening during power sharpening of about 5 points.”
What are “points”? Are you speaking or Rockwell C?
Can you point me to those studies?
Sorry, I reread my follow-up and meant to answer more directly. Yes, the drop was ~ 5 points in HRc. I have finally been able to get the link to the information, which is below. The hardness was actually measured in Vickers hardness, which is then converted. The original hardness is 59 to 60 HRc. The overheated hardness dropped to about 55, but only in the last 0.003 to 0.004 inches at the edge. There are some concerns regarding the test, but the information is not available to check the concerns. This includes things like belt speed, pressure, etc.
https://lh3.googleusercontent.com/-fcf1c0FRBWQ/VqbHkj8wOSI/AAAAAAAAGzE/Im-EQpA5uQ4/s912-Ic42/Shears.png
RE: Salutations to Stone Sharpeners! - Rupert Lucius - 01-02-2018
Me2
Great information - for sure I can/will continue to use my Viel (variable speed), SM1 (variable speed) and my water cooled Tormeks, without fear of damaging my Wife's kitchen knives and my pocket knives ZDP 189's.
Thank you for this info, I, was in a holding pattern waiting on this validation.
Again thanks and as always
Rupert
RE: Salutations to Stone Sharpeners! - me2 - 01-02-2018
Mr. Lucius, tapered blades are often a problem. Many times people will use a coupon during heat treatment testing, with flat sides and polished. Going a step further is having it mounted and polished to allow the most accurate measure possible. Polishing and microhardness testing is going yet a step further.
I have never used hardness files. I have heard of blades skating a file, yet when checked under magnification, had a much softer structure than intended. Conversely, it's not unheard of for someone to fail to consider the decarburization that can happen on the surface of steel pieces, and try file testing only to come away with the impression their steel didn't harden. After filing more, they discover they just didn't go deep enough and are elated to find their steel did exactly what they wanted.
Assuming the steel in the shears was a fairly simple carbon steel, the hardness drop indicates temperatures in the range of 500 to 700 degrees F, depending upon steel, though to loose hardness in such a short time, it was probably higher. Stainless steels are generally more resistant to softening than that, and common kitchen knives are generally quite soft anyway, and so may not soften at all. There are a huge number of variables, from steel type, abrasive type, cooled, fast, slow, etc. Power sharpening without coolant doesn't always cause issues, and water or oil cooled sharpening can still cause burning. Sparks are no guarantee of overheating, as iron/steel powder (and many other metal powders) can auto-ignite during grinding, causing sparks. The only way to sort it out is to find a reliable way to evaluate the end result, which in our case on this forum is initial sharpness and it's longevity.
Again, I am surprised at how controversial this topic can become. I think it's perfectly reasonable for anyone who sharpens with powered equipment to consider overheating. It's possible to do without even knowing. Fortunately, using and/or testing the knife will reveal the problem. As long as there isn't gross overheating where color changes are evident, it can be remedied fairly easily.
All these issues are avoidable with enough experience, information, and a way to examine the results. Edge holding tests with the EOU sharpness devices are one way to examine the edge, both before and during use/testing.
RE: Salutations to Stone Sharpeners! - EOU - 01-02-2018
In the words of that great 20th century philosopher Rodney King "Can we all just get along?" We've seen nothing printed in this thread from which umbrage should be taken by any party. No one here is the final arbiter of truth. All thoughts and opinions should be freely expressed as long as they are respectful of the opinions held by others. Please don't let a really interesting discussion devolve into a tribal dispute. If you think that my Kally is overheating my edges then I think your stone is going to slide off the table and fall on your foot. We'll live with and love our overheated edges and you'll learn how to walk with a broken toe. Then we can continue to be friends. This would be a great time for everyone to stand back, take a deep breath and then continue the discussion...as friends and fellow Exchange members.
RE: Salutations to Stone Sharpeners! - scott.livesey - 01-03-2018
I think the take away should be that improper technique or equipment can cause the edge to overheat when power sharpening. there are numerous ways to prevent this from happening. as a maker I have a responsibility not to sell a blade with an overheated edge. as a knife owner, not overheating the edge should improve blade life.
here is a link to a lengthy discussion on the subject. http://www.hypefreeblades.com/forum/viewtopic.php?f=3&t=391&start=50
RE: Salutations to Stone Sharpeners! - grepper - 01-03-2018
I’ve been enjoying this thread, and find it very informative and interesting especially considering I sharpen with a Kally. The funny thing is that I agree with everybody! Is there heating? Yes. Is it manageable? Yes. Is it worth discussing and understanding? Yes.
I agree with Mr. Me2 when he states, “All these issues are avoidable with enough experience, information, and a way to examine the results.”, and with Mr. Livesey when he said, “I think the take away should be that improper technique or equipment can cause the edge to overheat when power sharpening. There are numerous ways to prevent this from happening.”
One thing about the physical world, and life in general I suppose, is that there is never a free lunch. It’s always a give and take, a balancing act. You cannot sharpen without generating heat. In this case however, I think, (pun intended), it is simply a matter of degree°.
The fun and interesting part is that we are exploring the issue.
RE: Salutations to Stone Sharpeners! - Jan - 01-04-2018
In Newton’s time there was confusion between heat and temperature concept. I was surprised that in this country, more than 300 years later, people often think that heat and temperature are the same thing.
There exist a fine demarking line between heat and temperature. Heat is the amount of energy in a body while temperature is something that measures the intensity of heat.
The main feature of heat is that it travels from heat region (e.g. the edge) to cooler region (the blade) while temperature raises when heated and falls when cooled.
Heat has the ability to work while temperature can only be used to measure the degree of heat.
The US commonly uses Fahrenheit temperature scale on which water freezes at 32°F and boils at 212°F.
Most of the world uses the Celsius scale on which water freezes at 0°C and boils at 100°C.
The temperature of absolute zero occurs at -460°F or -273°C. Nobody has touched the temperature of absolute zero.
Very small amount of heat generated during grinding can cause very large temperature increase provided the heat is transferred to a very small segment of the edge. The flash heating/temperature occurs during micro-second of time and the size of the heated edge segment may be as small as one micro-meter.
At the microscopic scale we have to rely on information provided by suitable sensitive instruments.
Jan
RE: Salutations to Stone Sharpeners! - grepper - 01-04-2018
Mr. Jan uttered, “The flash heating/temperature occurs during micro-second of time and the size of the heated edge segment may be as small as one micro-meter.”
And that is where I think some of the confusion in this thread stems from. It is one thing to consider what is happening at the microscopic level, but quit another when considering macro affects on the blade.
RE: Salutations to Stone Sharpeners! - Jan - 01-04-2018
Mr. Grepper, you are correct, the flash heating leading to flash temperatures occurs at the microscopic scale.
When the heat pulses are not very frequent (light touch sharpening) then they will not heat up the whole edge – grindstone contact area and will cause no macroscopically measurable changes of edge hardness.
The open question for me is whether on the microscopic scale some tiny edge defects, caused by the flash temperatures, exists?
Jan