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#41
Posted to rec.knives,rec.crafts.woodturning,rec.crafts.metalworking,sci.physics,sci.engr.mech
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__measure__ sharpness ?
wrote in message ... If you cut Anything, you have 'damaged' the edge. Oooo... that's where knife blades made from all-hard ~65hrc HSS power hacksaw blades... come into the picture. Maybe not the sharpest edge obtainable but will sure as heck get sharp and cut a lot of stuff before you notice much difference. http://www.panix.com/~alvinj/HSSknife.htm Alvin in AZ But one poster was right when he pointed out that what is or is not sharp often depends on what you are cutting and how you are cutting it. Then there is the issue of fragile... An awful lot of different methods, metals, blade shapes, etc. do okay but... To some degree I guess each to his own. It's like what is a good knife or what knife is best for survival? I'd say the one you have is the best one to use. Some knives may actually be better at some tasks than others but most are passable at any reasonable task at least with a little practice. I just hope the user knows how to take care of it and know how to use it. I also hope the user has been reasonable and prudent before hand. Prevention beats a mountain of mending. |
#42
Posted to rec.knives,rec.crafts.woodturning,rec.crafts.metalworking,sci.physics,sci.engr.mech
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__measure__ sharpness ?
The professional equipment comes from Catra http://catra.org/ IT is
expensive. A reasonable priced method has been developed and used by Cliff Stamp http://www.cutleryscience.com/review...html#sharpness Steve Sharpening Made Easy: A Primer on Sharpening Knives and Other Edged Tools by Steve Bottorff www.sharpeningmadeeasy.com Remove REMOVE from address when replying wrote: can you imagine if the conventional wisdom for judging size-tolerance of fabricated-materials was along the lines of, "how does it feel when i shave hairs on my arm?" I want to _measure_ knife sharpness. In a repeatible, scientific way. And preferably, non-destructive to the sharpened edge! the floor is open for discussion. |
#43
Posted to rec.knives,rec.crafts.woodturning,rec.crafts.metalworking,sci.physics,sci.engr.mech
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__measure__ sharpness ?
There's so many posts in this thread that I haven't read them all yet, but I
feel compelled to point out that the original poster wanted to measure sharpness, NOT effectiveness. Although he didn't say why, it seems quite possible that he might just want to compare or measure sharpness for its own sake. Or for use with only one shape of blade and one type of material being cut. Maybe for just one specific knife, even, say his daily-carry pocket knife. DougVL "Brent" wrote in message oups.com... On Apr 12, 1:39 am, wrote: can you imagine if the conventional wisdom for judging size-tolerance of fabricated-materials was along the lines of, "how does it feel when i shave hairs on my arm?" I want to _measure_ knife sharpness. In a repeatible, scientific way. And preferably, non-destructive to the sharpened edge! the floor is open for discussion. the problem with SHARPNESS is it is not a good measure of the effectiveness of a cutting tool. so even quantifiabbly measuring sharpmess means nothing in itself. Sharpness will be like Watts in car stereos or Horsepower in motors and compressors The reason i say that is that the Cutting tool is dependent on the material being cut for its effectiveness. by knife standards a SAW is a thick flat edge with 0 sharpness but its very effective at cutting trees. If i use trees as an example try cutting a tree down with a splitting maul and you will be into one of the most frustrating experiences of your life. Just a little less so than splitting wood with a felling axe the felling axe is sharp and is made for cutting the splitting axe is meant for prying wood apart sharpness is not very useful to a splitting maul since it is serving as a LEVER not a blade Food Sharpness is a DETRIMENT to effectively slicing soft or airy foods. Take a loaf of bread, a tomato, and an appleas examples a Bread knife has a serrated edge and cuts with a sawing type motion because Bread is mostly air with fibres of bread itself tham move easily, its impossible to no have then crush someonwhat under an unfirm blade so a sharp sawing motion catches it A tomato is similar loose fibers in mostly water a knife with some roughness on the edge slices it BETTER that a purely sharp edge to avoid an apple is MUCH more firmly put together and a purely sharp edge cuts it better than the earlier two There are as many different ways to sharpen a blade as there are ways to prepare lathe toolbits. EVERY material does better with certain angles or feed types or feed speeds Sharp isnt everything but SOMETIMES sharpest is best other times it isnt But dont confuse a worn edge with an edge that is not sharp. I keep my pocket knife edge very fresh but at an angle to deal with anything i might come across (I dont measure it but it is likely about a 30 degree angle based on how i hold my hand while sharpening. It needs to still be in decent shape if i need to cut copper wires or strip coating or chop off plastic tiewraps i wont be using it for fine detailed cutting. But a filleting knife i would have sharpened to a FAR steeper angle for a far finer cut and so that it might wear down FAR faster if it was cutting anything firmer than a fish I can chop through copper cable with my pocketknife if i need to and then need to resharpen it at the end of the day. my kitchen knifes or chisels would have their edge ruined doing that immediately. Sorry for the long Post but the overall point of it is Sharpness is not a direct measure of effectiveness Brent Ottawa Canada |
#44
Posted to rec.knives,rec.crafts.woodturning,rec.crafts.metalworking,sci.physics,sci.engr.mech
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__measure__ sharpness ?
In rec.knives DougVL wrote:
There's so many posts in this thread that I haven't read them all yet, but I feel compelled to point out that the original poster wanted to measure sharpness, NOT effectiveness. Although he didn't say why, it seems quite possible that he might just want to compare or measure sharpness for its own sake. Or for use with only one shape of blade and one type of material being cut. Maybe for just one specific knife, even, say his daily-carry pocket knife. DougVL Yeah, it prob'ly got lost in there somewhere... a "sharpness test" -is-testing for cutting effectiveness, right? snipped Brent's post And yeah Brent took the ball and ran with it alright. But scored. Alvin in AZ |
#45
Posted to rec.knives,rec.crafts.woodturning,rec.crafts.metalworking,sci.physics,sci.engr.mech
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__measure__ sharpness ?
DougVL wrote:
There's so many posts in this thread that I haven't read them all yet, but I feel compelled to point out that the original poster wanted to measure sharpness, NOT effectiveness. Although he didn't say why, it seems quite possible that he might just want to compare or measure sharpness for its own sake. *Or for use with only one shape of blade and one type of material being cut. *Maybe for just one specific knife, even, say his daily-carry pocket knife. I did point out, (I seem to recall), that the only use I could see for such a test, was to judge a sharpness competition. -- Nomen Nescio |
#46
Posted to rec.knives,rec.crafts.woodturning,rec.crafts.metalworking,sci.physics,sci.engr.mech
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__measure__ sharpness ?
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#47
Posted to rec.knives,rec.crafts.woodturning,rec.crafts.metalworking,sci.physics,sci.engr.mech
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__measure__ sharpness ?
There's so many posts in this thread that I haven't read them all yet, but I
feel compelled to point out that the original poster wanted to measure sharpness, NOT effectiveness. I was just about to mention the same thing. If I wanted to measure something practical and physical, I'd look for existing testing methods from the experts at ASTM. www.astm.org Search for 'edge sharpness.' Dan |
#48
Posted to rec.knives,rec.crafts.woodturning,rec.crafts.metalworking,sci.physics,sci.engr.mech
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__measure__ sharpness ?
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#49
Posted to rec.knives,rec.crafts.woodturning,rec.crafts.metalworking,sci.physics,sci.engr.mech
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__measure__ sharpness ?
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#51
Posted to rec.knives,rec.crafts.woodturning,rec.crafts.metalworking,sci.physics,sci.engr.mech
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__measure__ sharpness ?
In article ,
"deowll" wrote: "Del Cecchi" wrote in message ... "Mitchell Jones" wrote in message ... wrote: can you imagine if the conventional wisdom for judging size-tolerance of fabricated-materials was along the lines of, "how does it feel when i shave hairs on my arm?" I want to _measure_ knife sharpness. In a repeatible, scientific way. And preferably, non-destructive to the sharpened edge! the floor is open for discussion. ***{You want to cut a homogeneous material that will not take the edge off of your blade. Use paraffin. You want the conditions to always be the same, so that you can compare results. Clamp the blade to be tested so that it forms the horizontal member of an isosceles triangle, the equal sides of which point downward. Hang a platform in the "V" and add weights until the blades cuts smoothly through the paraffin. The less weight required, the sharper the blade. Always use identical blocks of paraffin. The weight required, then, is the measure of dullness; its reciprocal is your measure of sharpness. Always include the weight of the "V" and the blade in the data you record. That should work. --Mitchell Jones}*** ************************************************** *************** If I seem to be ignoring you, consider the possibility that you are in my killfile. --MJ Scanning electron microscope. Agreed but with the observation that this won't tell you how well the edge will cut any give material to many things come into play. ***{The original poster wanted a technique that would measure the sharpness. The electron microscope would be utterly useless in that regard because it would provide an image of the edge, not a measure of sharpness. The main difficulty with measuring the force required to cut paraffin, on the other hand, is that force is required not merely to cut the paraffin, but also to slide the flat part of the blade against the flat part of the cut as the cutting edge moves through the material. All that is relevant to measure the sharpness is the part of the force which is required to get the cut started, not the part required to slide the blade along behind the cutting edge. Spraying all blades with WD40 before doing the test would eliminate a lot, but not all, of that. Another approach would be to clamp the blade in a horizontal position with its cutting edge upwards, and hang an empty, light-weight container from it by looping a piece of nylon fishing line of known quality around the blade. You could then pour water into the container slowly, until the weight was enough so that the sharp edge cut through the line. Catch the container as it falls and weigh it, and use the reciprocal of the weight as your measure of sharpness. That method would have the advantage of eliminating the force of sliding friction/adhesion from the measurement. While that method would provide a generalized measure of sharpness, it would not change the fact that the force required to make a cut would vary depending on the material, and, in particular, on the adhesive forces between the flat sides of the blade and the sides of the cut, as the blade moves along. It is simply a fact that the ease of cutting depends not merely on the sharpness of the cutting edge, but also on the adhesive forces between the blade and the material being cut. (Not to mention the fact that the cutting edge must hold its sharpness while the cut is being made. A copper blade will not hold its edge while cutting a steel wire, for example.) --Mitchell Jones}*** ************************************************** *************** If I seem to be ignoring you, consider the possibility that you are in my killfile. --MJ |
#52
Posted to rec.knives,rec.crafts.woodturning,rec.crafts.metalworking,sci.physics,sci.engr.mech
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__measure__ sharpness ?
"Mitchell Jones" wrote in message ... In article , "deowll" wrote: "Del Cecchi" wrote in message ... "Mitchell Jones" wrote in message ... wrote: can you imagine if the conventional wisdom for judging size-tolerance of fabricated-materials was along the lines of, "how does it feel when i shave hairs on my arm?" I want to _measure_ knife sharpness. In a repeatible, scientific way. And preferably, non-destructive to the sharpened edge! the floor is open for discussion. ***{You want to cut a homogeneous material that will not take the edge off of your blade. Use paraffin. You want the conditions to always be the same, so that you can compare results. Clamp the blade to be tested so that it forms the horizontal member of an isosceles triangle, the equal sides of which point downward. Hang a platform in the "V" and add weights until the blades cuts smoothly through the paraffin. The less weight required, the sharper the blade. Always use identical blocks of paraffin. The weight required, then, is the measure of dullness; its reciprocal is your measure of sharpness. Always include the weight of the "V" and the blade in the data you record. That should work. --Mitchell Jones}*** ************************************************** *************** If I seem to be ignoring you, consider the possibility that you are in my killfile. --MJ Scanning electron microscope. Agreed but with the observation that this won't tell you how well the edge will cut any give material to many things come into play. ***{The original poster wanted a technique that would measure the sharpness. The electron microscope would be utterly useless in that regard because it would provide an image of the edge, not a measure of sharpness. The main difficulty with measuring the force required to cut paraffin, on the other hand, is that force is required not merely to cut the paraffin, but also to slide the flat part of the blade against the flat part of the cut as the cutting edge moves through the material. All that is relevant to measure the sharpness is the part of the force which is required to get the cut started, not the part required to slide the blade along behind the cutting edge. Spraying all blades with WD40 before doing the test would eliminate a lot, but not all, of that. Another approach would be to clamp the blade in a horizontal position with its cutting edge upwards, and hang an empty, light-weight container from it by looping a piece of nylon fishing line of known quality around the blade. You could then pour water into the container slowly, until the weight was enough so that the sharp edge cut through the line. Catch the container as it falls and weigh it, and use the reciprocal of the weight as your measure of sharpness. That method would have the advantage of eliminating the force of sliding friction/adhesion from the measurement. While that method would provide a generalized measure of sharpness, it would not change the fact that the force required to make a cut would vary depending on the material, and, in particular, on the adhesive forces between the flat sides of the blade and the sides of the cut, as the blade moves along. It is simply a fact that the ease of cutting depends not merely on the sharpness of the cutting edge, but also on the adhesive forces between the blade and the material being cut. (Not to mention the fact that the cutting edge must hold its sharpness while the cut is being made. A copper blade will not hold its edge while cutting a steel wire, for example.) --Mitchell Jones}*** ************************************************** *************** If I seem to be ignoring you, consider the possibility that you are in my killfile. --MJ Fine, you don't like looking at the edge width and angle as a sharpness measure, even though "a knife is just a wedge". So then you need to write a definition of what the parameter you call "sharpness" is. Ability to push cut flimsy material? slice meat? indent paraffin? If you can define what you are looking to measure some genius in this group can suggest a method, some of which might work. But you can't measure what you haven't defined. del |
#53
Posted to rec.knives,rec.crafts.woodturning,rec.crafts.metalworking,sci.physics,sci.engr.mech
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__measure__ sharpness ?
In article ,
"Del Cecchi" wrote: "Mitchell Jones" wrote in message ... In article , "deowll" wrote: "Del Cecchi" wrote in message ... "Mitchell Jones" wrote in message ... wrote: can you imagine if the conventional wisdom for judging size-tolerance of fabricated-materials was along the lines of, "how does it feel when i shave hairs on my arm?" I want to _measure_ knife sharpness. In a repeatible, scientific way. And preferably, non-destructive to the sharpened edge! the floor is open for discussion. ***{You want to cut a homogeneous material that will not take the edge off of your blade. Use paraffin. You want the conditions to always be the same, so that you can compare results. Clamp the blade to be tested so that it forms the horizontal member of an isosceles triangle, the equal sides of which point downward. Hang a platform in the "V" and add weights until the blades cuts smoothly through the paraffin. The less weight required, the sharper the blade. Always use identical blocks of paraffin. The weight required, then, is the measure of dullness; its reciprocal is your measure of sharpness. Always include the weight of the "V" and the blade in the data you record. That should work. --Mitchell Jones}*** ************************************************** *************** If I seem to be ignoring you, consider the possibility that you are in my killfile. --MJ Scanning electron microscope. Agreed but with the observation that this won't tell you how well the edge will cut any give material to many things come into play. ***{The original poster wanted a technique that would measure the sharpness. The electron microscope would be utterly useless in that regard because it would provide an image of the edge, not a measure of sharpness. The main difficulty with measuring the force required to cut paraffin, on the other hand, is that force is required not merely to cut the paraffin, but also to slide the flat part of the blade against the flat part of the cut as the cutting edge moves through the material. All that is relevant to measure the sharpness is the part of the force which is required to get the cut started, not the part required to slide the blade along behind the cutting edge. Spraying all blades with WD40 before doing the test would eliminate a lot, but not all, of that. Another approach would be to clamp the blade in a horizontal position with its cutting edge upwards, and hang an empty, light-weight container from it by looping a piece of nylon fishing line of known quality around the blade. You could then pour water into the container slowly, until the weight was enough so that the sharp edge cut through the line. Catch the container as it falls and weigh it, and use the reciprocal of the weight as your measure of sharpness. That method would have the advantage of eliminating the force of sliding friction/adhesion from the measurement. While that method would provide a generalized measure of sharpness, it would not change the fact that the force required to make a cut would vary depending on the material, and, in particular, on the adhesive forces between the flat sides of the blade and the sides of the cut, as the blade moves along. It is simply a fact that the ease of cutting depends not merely on the sharpness of the cutting edge, but also on the adhesive forces between the blade and the material being cut. (Not to mention the fact that the cutting edge must hold its sharpness while the cut is being made. A copper blade will not hold its edge while cutting a steel wire, for example.) --Mitchell Jones}*** ************************************************** *************** If I seem to be ignoring you, consider the possibility that you are in my killfile. --MJ Fine, you don't like looking at the edge width and angle as a sharpness measure, even though "a knife is just a wedge". So then you need to write a definition of what the parameter you call "sharpness" is. Ability to push cut flimsy material? slice meat? indent paraffin? If you can define what you are looking to measure some genius in this group can suggest a method, some of which might work. But you can't measure what you haven't defined. ***{There is a difference between being able to define something in words that will communicate the meaning to others, and understanding what it is. In fact, you have to understand a concept before you can convey it to others. For example, most people who understand how to ride a bicycle would have great difficulty conveying the technique in words, yet they can most assuredly get on a bicycle and ride it. If I were to describe the technique in words, I would simply tell the other person to turn in the direction that will keep the bottom of the front wheel beneath the center of the handle bars. Measuring sharpness, like riding a bicycle, requires understanding, but does not require the ability to communicate that understanding. Most people have an understanding of what sharpness is, and, thus, could competently attempt to measure it, but would have to struggle a bit to define it. Since you want a definition, I would describe it as the ease with which the edge of a blade separates the material being cut. That concept relates directly to the measuring technique I described yesterday because ease is inversely proportional to the force required, and, since we are talking about the edge only, the force required to move the rest of the blade through the cut is irrelevant. I would note, however, that I came up with the measuring technique yesterday and the definition today. Hence the ability to measure sharpness only required understanding. I was able to measure what I had not defined. Of course, the more you work with a concept, the better you understand it, and putting it into words is an instance of working with it. Thus defining something enhances one's understanding, even though it is not a prerequisite of understanding. --Mitchell Jones}*** del ************************************************** *************** If I seem to be ignoring you, consider the possibility that you are in my killfile. --MJ |
#54
Posted to rec.knives,rec.crafts.woodturning,rec.crafts.metalworking,sci.physics,sci.engr.mech
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__measure__ sharpness ?
Mitchell Jones wrote:
In article , "Del Cecchi" wrote: "Mitchell Jones" wrote in message ... In article , "deowll" wrote: "Del Cecchi" wrote in message ... "Mitchell Jones" wrote in message ... wrote: can you imagine if the conventional wisdom for judging size-tolerance of fabricated-materials was along the lines of, "how does it feel when i shave hairs on my arm?" I want to _measure_ knife sharpness. In a repeatible, scientific way. And preferably, non-destructive to the sharpened edge! the floor is open for discussion. ***{You want to cut a homogeneous material that will not take the edge off of your blade. Use paraffin. You want the conditions to always be the same, so that you can compare results. Clamp the blade to be tested so that it forms the horizontal member of an isosceles triangle, the equal sides of which point downward. Hang a platform in the "V" and add weights until the blades cuts smoothly through the paraffin. The less weight required, the sharper the blade. Always use identical blocks of paraffin. The weight required, then, is the measure of dullness; its reciprocal is your measure of sharpness. Always include the weight of the "V" and the blade in the data you record. That should work. --Mitchell Jones}*** ******************************************** ********************* If I seem to be ignoring you, consider the possibility that you are in my killfile. --MJ Scanning electron microscope. Agreed but with the observation that this won't tell you how well the edge will cut any give material to many things come into play. ***{The original poster wanted a technique that would measure the sharpness. The electron microscope would be utterly useless in that regard because it would provide an image of the edge, not a measure of sharpness. The main difficulty with measuring the force required to cut paraffin, on the other hand, is that force is required not merely to cut the paraffin, but also to slide the flat part of the blade against the flat part of the cut as the cutting edge moves through the material. All that is relevant to measure the sharpness is the part of the force which is required to get the cut started, not the part required to slide the blade along behind the cutting edge. Spraying all blades with WD40 before doing the test would eliminate a lot, but not all, of that. Another approach would be to clamp the blade in a horizontal position with its cutting edge upwards, and hang an empty, light-weight container from it by looping a piece of nylon fishing line of known quality around the blade. You could then pour water into the container slowly, until the weight was enough so that the sharp edge cut through the line. Catch the container as it falls and weigh it, and use the reciprocal of the weight as your measure of sharpness. That method would have the advantage of eliminating the force of sliding friction/adhesion from the measurement. While that method would provide a generalized measure of sharpness, it would not change the fact that the force required to make a cut would vary depending on the material, and, in particular, on the adhesive forces between the flat sides of the blade and the sides of the cut, as the blade moves along. It is simply a fact that the ease of cutting depends not merely on the sharpness of the cutting edge, but also on the adhesive forces between the blade and the material being cut. (Not to mention the fact that the cutting edge must hold its sharpness while the cut is being made. A copper blade will not hold its edge while cutting a steel wire, for example.) --Mitchell Jones}*** *********************************************** ****************** If I seem to be ignoring you, consider the possibility that you are in my killfile. --MJ Fine, you don't like looking at the edge width and angle as a sharpness measure, even though "a knife is just a wedge". So then you need to write a definition of what the parameter you call "sharpness" is. Ability to push cut flimsy material? slice meat? indent paraffin? If you can define what you are looking to measure some genius in this group can suggest a method, some of which might work. But you can't measure what you haven't defined. ***{There is a difference between being able to define something in words that will communicate the meaning to others, and understanding what it is. In fact, you have to understand a concept before you can convey it to others. For example, most people who understand how to ride a bicycle would have great difficulty conveying the technique in words, yet they can most assuredly get on a bicycle and ride it. If I were to describe the technique in words, I would simply tell the other person to turn in the direction that will keep the bottom of the front wheel beneath the center of the handle bars. Measuring sharpness, like riding a bicycle, requires understanding, but does not require the ability to communicate that understanding. Most people have an understanding of what sharpness is, and, thus, could competently attempt to measure it, but would have to struggle a bit to define it. Since you want a definition, I would describe it as the ease with which the edge of a blade separates the material being cut. That concept relates directly to the measuring technique I described yesterday because ease is inversely proportional to the force required, and, since we are talking about the edge only, the force required to move the rest of the blade through the cut is irrelevant. I would note, however, that I came up with the measuring technique yesterday and the definition today. Hence the ability to measure sharpness only required understanding. I was able to measure what I had not defined. Of course, the more you work with a concept, the better you understand it, and putting it into words is an instance of working with it. Thus defining something enhances one's understanding, even though it is not a prerequisite of understanding. --Mitchell Jones}*** del ************************************************** *************** If I seem to be ignoring you, consider the possibility that you are in my killfile. --MJ By inventing the measurement process and using that to define the parameter you haven't produced anything valid. You have merely asserted a particular meaning for "sharpness". If I used a pork chop or a 2 by 4 instead of paraffin I would get different values and perhaps even different ordering. And if I did slicing motion instead of push, they would be different still. And why ignore the friction with the sides of the blade? Isn't that an important component of cutting? I don't know what group you are posting from but after this I will be trimming followups and crossposting to rec.knives. -- Del Cecchi "This post is my own and doesn’t necessarily represent IBM’s positions, strategies or opinions.” |
#55
Posted to rec.knives,rec.crafts.woodturning,rec.crafts.metalworking,sci.physics,sci.engr.mech
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__measure__ sharpness ?
Mitchell Jones wrote:
Del Cecchi wrote: By inventing the measurement process and using that to define the parameter you haven't produced anything valid. ***{My purpose was to provide the original poster with what he requested: a method of comparing the sharpness of various blades that will not degrade the edges, and will be in accord with our notions of what sharpness means. If I succeed in doing that, I will be satisfied. --MJ}*** You have merely asserted a particular meaning for "sharpness". If I used a pork chop or a 2 by 4 instead of paraffin I would get different values and perhaps even different ordering. ***{That's right, and the reason is due to the variations in the force required to slide the sides of the blade past the material. All we are really concerned with is the force required to get the edge to slice through the surface of the material. The deeper it is embedded into whatever is being cut, the larger the adhesive/frictional force that must be overcome, because that is proportional to the areas that are in contact, and is clearly not relevant to the issue of sharpness. Result: in my previous post, I specified a better method than the one involving use of paraffin: clamp the blade horizontally, edge upward, and pass a small diameter nylon fishing line over the edge of the blade, and down to support a water container. (Use the same type of line for all measurements.) Add water to the container until the blade cuts through the fishing line, weigh the container, take the reciprocal, and that's your measure of sharpness. Result: only the force required to get the edge through the line is measured, not the irrelevant force of adhesion between the sides of the blade and the sides of the cut. I should note, by the way, that the likely reason you forgot that I had already abandoned the paraffin method, was that you did not insert your comments after the comments of mine to which you were responding. If you had done so, you could not have failed to notice that the horse you were focused on was already out of the barn, so to speak. What this illustrates is why, on usenet, top posting and bottom posting are a no-no. It is always best to insert your comments after the specific remarks to which you are responding. --MJ}*** And if I did slicing motion instead of push, they would be different still. ***{It would be very difficult to ensure that the slicing motion was the same in all cases, so I would not recommend that method. Concerning the earlier method, if a spool of nylon fishing line were used, you could easily create a setup designed for multiple measurements. In each case, you would begin by pulling out enough line to pass over the edge of the blade and down to the water container, where you would clamp it. Next, clamp the spool so it will not turn, add water to the container until the line is severed, weigh container and water with the detached segment of line still attached, jot down the weight, discard the piece of line, pour out the water, and repeat the procedure for the next blade. That should make it easy to compare the sharpness of various blades, and I would expect the ordering to be consistent so long as the line used was made of softer material than the blade being used to cut it. (Steel line and a copper blade, as noted earlier, would not work.) --Mitchell Jones}*** And why ignore the friction with the sides of the blade? Isn't that an important component of cutting? ***{Ease of cutting does not merely depend on the sharpness of the blade, but also on the characteristics of the material being cut. The original poster asked for a measure of sharpness, not for a measure of how easy it would be to cut a particular material. If he had asked for the latter, I would not have bothered to respond, since the only way to determine how easy a particular material is to cut is to do experiments with that particular material, using blades of various types. --MJ}*** I don't know what group you are posting from ***{I'm posting from sci.physics. --MJ}*** but after this I will be trimming followups and crossposting to rec.knives. ***{In my view, the original poster did a good job of selecting groups where this discussion might be of interest, and I see no reason to change them at this point. --MJ}*** ************************************************** *************** If I seem to be ignoring you, consider the possibility that you are in my killfile. --MJ |
#56
Posted to rec.knives,rec.crafts.woodturning,rec.crafts.metalworking,sci.physics,sci.engr.mech
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__measure__ sharpness ?
"Mitchell Jones" wrote in message ... Mitchell Jones wrote: Del Cecchi wrote: By inventing the measurement process and using that to define the parameter you haven't produced anything valid. ***{My purpose was to provide the original poster with what he requested: a method of comparing the sharpness of various blades that will not degrade the edges, and will be in accord with our notions of what sharpness means. If I succeed in doing that, I will be satisfied. --MJ}*** You have merely asserted a particular meaning for "sharpness". If I used a pork chop or a 2 by 4 instead of paraffin I would get different values and perhaps even different ordering. ***{That's right, and the reason is due to the variations in the force required to slide the sides of the blade past the material. All we are really concerned with is the force required to get the edge to slice through the surface of the material. The deeper it is embedded into whatever is being cut, the larger the adhesive/frictional force that must be overcome, because that is proportional to the areas that are in contact, and is clearly not relevant to the issue of sharpness. Why isn't it relevant? Many cutting tasks involve things of non negligible thickness. Result: in my previous post, I specified a better method than the one involving use of paraffin: clamp the blade horizontally, edge upward, and pass a small diameter nylon fishing line over the edge of the blade, and down to support a water container. (Use the same type of line for all measurements.) Add water to the container until the blade cuts through the fishing line, weigh the container, take the reciprocal, and that's your measure of sharpness. Result: only the force required to get the edge through the line is measured, not the irrelevant force of adhesion between the sides of the blade and the sides of the cut. I should note, by the way, that the likely reason you forgot that I had already abandoned the paraffin method, was that you did not insert your comments after the comments of mine to which you were responding. If you had done so, you could not have failed to notice that the horse you were focused on was already out of the barn, so to speak. What this illustrates is why, on usenet, top posting and bottom posting are a no-no. It is always best to insert your comments after the specific remarks to which you are responding. Actually it is because I skipped several posts in the thread. --MJ}*** And if I did slicing motion instead of push, they would be different still. ***{It would be very difficult to ensure that the slicing motion was the same in all cases, so I would not recommend that method. So it is not a valid alternative because it is hard? Better give up the particle accelerators then. Concerning the earlier method, if a spool of nylon fishing line were used, you could easily create a setup designed for multiple measurements. In each case, you would begin by pulling out enough line to pass over the edge of the blade and down to the water container, where you would clamp it. Next, clamp the spool so it will not turn, add water to the container until the line is severed, weigh container and water with the detached segment of line still attached, jot down the weight, discard the piece of line, pour out the water, and repeat the procedure for the next blade. That should make it easy to compare the sharpness of various blades, and I would expect the ordering to be consistent so long as the line used was made of softer material than the blade being used to cut it. (Steel line and a copper blade, as noted earlier, would not work.) --Mitchell Jones}*** And why ignore the friction with the sides of the blade? Isn't that an important component of cutting? ***{Ease of cutting does not merely depend on the sharpness of the blade, but also on the characteristics of the material being cut. The original poster asked for a measure of sharpness, not for a measure of how easy it would be to cut a particular material. If he had asked for the latter, I would not have bothered to respond, since the only way to determine how easy a particular material is to cut is to do experiments with that particular material, using blades of various types. --MJ}*** I don't know what group you are posting from ***{I'm posting from sci.physics. --MJ}*** but after this I will be trimming followups and crossposting to rec.knives. ***{In my view, the original poster did a good job of selecting groups where this discussion might be of interest, and I see no reason to change them at this point. --MJ}*** ok, whatever you say. ************************************************** *************** If I seem to be ignoring you, consider the possibility that you are in my killfile. --MJ |
#57
Posted to rec.knives,rec.crafts.woodturning,rec.crafts.metalworking,sci.physics,sci.engr.mech
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__measure__ sharpness ?
On 8 mei, 05:45, "Del Cecchi" wrote:
"Mitchell Jones" wrote in message ***{That's right, and the reason is due to the variations in the force required to slide the sides of the blade past the material. All we are really concerned with is the force required to get the edge to slice through the surface of the material. The deeper it is embedded into whatever is being cut, the larger the adhesive/frictional force that must be overcome, because that is proportional to the areas that are in contact, and is clearly not relevant to the issue of sharpness. Why isn't it relevant? Many cutting tasks involve things of non negligible thickness. Because you're measuring blade sharpness, not sharpness + some other factors involving friction and target geometry. While we rec.knives types are all about practicality, if you want to measure and quantify things scientifically you have to isolate factors as much as possible. Ultimately, a blade's utility is down to several things; sharpness, geometry, rigidity, the target material... there's a mental tendency to lump this all in to "sharpness", because that's a handy word to use for how easily a knife cuts through something, but it's not accurate. ***{It would be very difficult to ensure that the slicing motion was the same in all cases, so I would not recommend that method. So it is not a valid alternative because it is hard? Better give up the particle accelerators then. Particle accelerators make it *easy* to reproduce conditions, that's why they cost so much. Put practically, it could be a very expensive process to create a repeatable and standardised slicing motion. Cheers Rich |
#58
Posted to rec.knives,rec.crafts.woodturning,rec.crafts.metalworking,sci.physics,sci.engr.mech
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__measure__ sharpness ?
On Apr 12, 7:57 pm, "Brent" wrote:
On Apr 12, 1:39 am, wrote: the problem with SHARPNESS is it is not a good measure of the effectiveness of a cutting tool.... I have to agree w/ Brent. Anyway, I thought this info tidbit might be of some interest. Once upon a time (25 years ago)... I worked in a Histology lab -a medical laboratory responsible for preparing surgically removed biopsies for microscopic review and diagnosis by a pathologist. The specimens were cut into approx 1/4" or smaller samples and processed, eventually embedding them into a block of paraffin wax. Three to eight micron thick slices of this embedded tissue were cut using a microtome and then mounted onto a microscopic slide for staining and review by the pathologist. Any knife nicks caused drag marks and compression of the tissue (and cells) making the sample of no value under the microscope. Some tissues contained bone and other harder stuff like kidney stones or even teeth (rare). The microtome consisted of an 8-10 inch knife fixed in position at an angle of roughly 30 degrees from the verticle, and a mounted block of tissue (about 1 in sq.) which passed over the knife, one rotation at a time, producing this thin tissue slice similar to a peeling cut in woodturning. The knife was of a fine grained steel... (sorry but I didn't know anything about steel at the time) and shaped like a wedge, about 30 degrees and 1 1/2 inches deep (8-10 inches long). The edge was sharpened on a super flat, ectched, thick glass plate using some watery toothpaste-like slurry. The blade was held at an angle and passed over the plate in a figure eight pattern, then flipped over to sharpen the other side. The passes were made mechanically and were counted and timed. (Keeping the angles even) Each knife had its own glass plate. Eventually, the glass plates were sent out for resurfacing; i.e. etchnig and flattening. And getting back to the point of the story: In the end, blade sharpness was determined by looking at the cutting edge under a microscope. Any knicks or voids left on the edge caused the blade to be resharped until removed. But ultimately, the sharpness test was how well it cut through the tissue samples. Some knives lasted for only say 30 slices. Others would last for several tissue blocks. Take what you can from this example. I thought it might give some perspective. June in Denver |
#59
Posted to rec.knives,rec.crafts.woodturning,rec.crafts.metalworking,sci.physics,sci.engr.mech
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__measure__ sharpness ?
"Mitchell Jones" wrote in message ... wrote: can you imagine if the conventional wisdom for judging size-tolerance of fabricated-materials was along the lines of, "how does it feel when i shave hairs on my arm?" I want to _measure_ knife sharpness. In a repeatible, scientific way. And preferably, non-destructive to the sharpened edge! the floor is open for discussion. ***{You want to cut a homogeneous material that will not take the edge off of your blade. Use paraffin. You want the conditions to always be the same, so that you can compare results. Clamp the blade to be tested so that it forms the horizontal member of an isosceles triangle, the equal sides of which point downward. Hang a platform in the "V" and add weights until the blades cuts smoothly through the paraffin. The less weight required, the sharper the blade. Always use identical blocks of paraffin. The weight required, then, is the measure of dullness; its reciprocal is your measure of sharpness. Always include the weight of the "V" and the blade in the data you record. That should work. As can be seen from experiments on shaving blades, the sharpness is somewhat a function of the chemistry of the thing to be cut, so perhaps it would be best to have the blade cut the material involved. If this is a non-destructive, production test, and speed is required, you extrude the material to be cut through a small hole, and slice the material using a tiny edge of the production item, using a photo-optical device to determine when the material was cut. You could use increasing air pressure or move a mass along a balance beam to apply force to the blades. If the blades are the same mass, and the test is go/no go, you could drop the blades on the material, and have the blades that don't cut through stick to the material and be carried away or deflected away from the "good" blades. -- Tom Potter *** Time Magazine Person of the Year 2006 *** http://home.earthlink.net/~tdp http://tdp1001.googlepages.com/home http://no-turtles.com http://www.frappr.com/tompotter http://photos.yahoo.com/tdp1001 http://spaces.msn.com/tdp1001 http://www.flickr.com/photos/tom-potter http://tom-potter.blogspot.com |
#60
Posted to rec.knives,rec.crafts.woodturning,rec.crafts.metalworking,sci.physics,sci.engr.mech
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__measure__ sharpness ?
According to jdturner :
On Apr 12, 7:57 pm, "Brent" wrote: the problem with SHARPNESS is it is not a good measure of the effectiveness of a cutting tool.... [ ... ] Anyway, I thought this info tidbit might be of some interest. Once upon a time (25 years ago)... [ ... ] The microtome consisted of an 8-10 inch knife fixed in position at an angle of roughly 30 degrees from the verticle, and a mounted block of tissue (about 1 in sq.) which passed over the knife, one rotation at a time, producing this thin tissue slice similar to a peeling cut in woodturning. The knife was of a fine grained steel... (sorry but I didn't know anything about steel at the time) and shaped like a wedge, about 30 degrees and 1 1/2 inches deep (8-10 inches long). The ones which I have can easily be described as being like straight razor blades on steroids. :-) The edge was sharpened on a super flat, ectched, thick glass plate using some watery toothpaste-like slurry. The blade was held at an angle and passed over the plate in a figure eight pattern, then flipped over to sharpen the other side. The passes were made mechanically and were counted and timed. (Keeping the angles even) Each knife had its own glass plate. Eventually, the glass plates were sent out for resurfacing; i.e. etchnig and flattening. Aha! This is useful information -- and probably explains the handles which came with the blades -- for sharpening -- not for the cutting of the slices. (I've owned a bladeless microtome for decades, and only fairly recently did I get some blades for it from an eBay auction.) I'll eventually need to sharpen those blades. Enjoy, DoN. -- Email: | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
#61
Posted to rec.knives,rec.crafts.woodturning,rec.crafts.metalworking,sci.physics,sci.engr.mech
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__measure__ sharpness ?
Guys,
Why not simply ask a razor blade engineer how THEY measure sharpness? Bill -- http://nmwoodworks.com/cube --- avast! Antivirus: Outbound message clean. Virus Database (VPS): 000738-4, 05/07/2007 Tested on: 5/9/2007 12:27:28 AM avast! - copyright (c) 1988-2007 ALWIL Software. http://www.avast.com |
#62
Posted to rec.knives,rec.crafts.woodturning,rec.crafts.metalworking,sci.physics,sci.engr.mech
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__measure__ sharpness ?
I don't know what group you are posting from but after this I will be
trimming followups and crossposting to rec.knives. Del Cecchi sir, may i respectfully request that you do not edit the follow-ups of my thread. each group was included for a reason. There is no redundancy available for cleaning up. i promise not to screw around with your threads. thank you for this basic courtesy. |
#63
Posted to rec.knives,rec.crafts.woodturning,rec.crafts.metalworking,sci.physics,sci.engr.mech
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__measure__ sharpness ?
Why not simply ask a razor blade engineer how THEY measure sharpness?
I did spend some time searching. I could not find a trade group with a close-enough specific focus. As far as I can tell, most of the blades sold in the USA (including the multi ones) are sourced from Korea. I am very open to corrections on both points. |
#64
Posted to rec.knives,rec.crafts.woodturning,rec.crafts.metalworking,sci.physics,sci.engr.mech
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__measure__ sharpness ?
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#65
Posted to rec.knives,rec.crafts.woodturning,rec.crafts.metalworking,sci.physics,sci.engr.mech
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__measure__ sharpness ?
In article , wrote:
In rec.knives wrote: I don't know what group you are posting from but after this I will be trimming followups and crossposting to rec.knives. Del Cecchi sir, may i respectfully request that you do not edit the follow-ups of my thread. each group was included for a reason. There is no redundancy available for cleaning up. i promise not to screw around with your threads. thank you for this basic courtesy. It wasn't "your thread" he was messing with... it was his "own post" he limited to where it went. ***{Yes, but he also mentioned that he was going to set followups. When a person sets followups, he determines where replies to his post will go. It is an option that, 99% of the time, is used maliciously. What usually happens is that some nut job posts something--usually name calling--into a thread, but sets followups so that if anyone replies to his ravings, their reply will not go where his post appeared, but somewhere else. Result: the person who replied watches the groups for awhile, waiting for his reply to appear. When it doesn't, he eventually reposts--and the same thing happens again! Eventually he notices that the newsgroups line on his replies keeps changing, and, finally, he notices a line in the post he is replying to that says "Set followups to alt.mother****ers," or something similar. In my view, the "Set followups" option is an abomination that should not exist. A poster should have control of where his own posts go, but should not have the power to mess with where replies to his post will go. If a person responding to a post wants his reply to not go to the same newsgroups as the post to which he is replying, he could always take action to make that happen. If he doesn't take such action, that ought to settle the matter. But, unfortunately, if "Set followups" has been invoked by the previous poster, his intentions will not be carried out unless he deliberately intervenes to undo the effects of "Set followups." Result: we all face the threat, whenever we post, that our replies will go somewhere other than where we intend them to go. There are basically two ways to deal with the threat posed by "set followups": (1) A person can get in the habit of always carefully examining the header information in any post to which he replies, to make sure followups have not been set, and, if they have, he can take action to deliberately undo the effect. (2) He can ignore the threat and, in those cases where he subsequently discovers that someone has used that option to redirect his replies, he can killfile the offending party, to ensure that it doesn't happen again. (If you never see his posts, you will never reply to them, and, thus, the followups he sets will never apply to you.) How does one choose between (1) and (2)? Simple: option (2) is easier, and, in addition, the fact that it is possible to set followups doesn't make it a moral thing to do. Setting followups reveals a character flaw which ought to be punished, and the killfile provides an ideal means to that end. Thus option number (2), in my view, is the only way to go. --Mitchell Jones}*** The courtesy was to limit his post to those he'd figured would be interested in -his- answer. ***{And the discourtesy was the threat of setting followups. If he had actually done that, rather than merely talking about doing it, he would have earned himself a place in a lot of killfiles, mine included. --MJ}*** Got that? And it's a basic courtesy to use your friggin name. ***{Not required, and for a good reason: these are open groups. Anyone can post here, and anyone can lurk--including certifiable lunatics, serial murderers, rapists, kidnappers, and others. Thus if that state of affairs renders some nervous about using their real names, it ought to be their call, just as where their replies go ought to be their call. Women and children, in particular, ought to be hesitant about using their real names. Bottom line: there is no rule of etiquette on usenet requiring that a person use his real name, nor should there be. --MJ}*** Also a thread "belongs" to those that -add- to it. Alvin been on NG's for ~12 years in AZ ************************************************** *************** If I seem to be ignoring you, consider the possibility that you are in my killfile. --MJ |
#66
Posted to rec.knives,rec.crafts.woodturning,rec.crafts.metalworking,sci.physics,sci.engr.mech
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__measure__ sharpness ?
In rec.knives Mitchell Jones wrote:
In my view, the "Set followups" option is an abomination that should not exist. A poster should have control of where his own posts go, but should not have the power to mess with where replies to his post will go. I couldn't disagree with you more. :/ Many times we get political or other off topic stuff in rec.knives like our few posts here for example. We know each other. We want to make a comment on the spam post but don't want our post going all over to the odd newsgroups and maybe just want to limit the discussion to r.k ...or maybe "alt.texas.guns" where some might actually be interrested in my dumb-ass comments. a.t.g (or whatever) is not added to the list, just not subtracted from the list. You are thinking "malicious use" and I am thinking "useful use" of the follow-up control. Do you always think negatively? Sometimes cross posting works out really cool with our sister NG alt.crafts.blacksmithing or used-to before it died... sci.engr.metallurgy. If a person responding to a post wants his reply to not go to the same newsgroups as the post to which he is replying, he could always take action to make that happen... The poster needs to pay attention? Or something? If he doesn't take such action, that ought to settle the matter. But, unfortunately, if "Set followups" has been invoked by the previous poster, his intentions will not be carried out unless he deliberately intervenes to undo the effects of "Set followups." Result: we all face the threat, whenever we post, that our replies will go somewhere other than where we intend them to go. No. :/ Not mine at least I use Tin and Pico and I know where they are going. Besides Del said what he did in his post. It was his post he gets to do with it what he friggin wants. Right? You get the same priv'lage. (1) A person can get in the habit of always carefully examining the header information in any post to which he replies, to make sure followups have not been set, and, if they have, he can take action to deliberately undo the effect. You don't do that everytime there maybe a question of hanky panky? ...he can killfile the offending party... Kill files are for sissys! :/ Setting followups reveals a character flaw which ought to be punished... --Mitchell Jones}*** Punished? By who? Using who's standards? ...Yours? LOL This is friggin usenet, it's open to the world. I know why gov't controls every****inthing it's people like MJ in there finding fault with everything and boogie men everyhwere. Will anyone in Steve's "fan club" agree with me on this? Alvin on r.k in AZ ps- MJ, if I knew where you were, I'd trimmed my post and it's follow-ups to our-two NGs |
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