zyhano
Gold Member
- Joined
- Dec 3, 2009
- Messages
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Hi boys and girls,
when talking about sharpening there is always a need to classify what the abrasives on the sharpening medium is so we have a way of comparing the different sharpening tools by different manufacturers out there.
In this post I will explain what abrasives are, what makes them a good abrasive, where you should use them and how we should describe them.
what are the factors for a good abrasive?
Particle size or particle size distribution (the average size) is an important part of the equation to get an edge that is worth calling sharp. It is important for the working speed of the abrasive and for the amount of metal that will be removed (at the scale of the abrasive). Larger particles will remove larger pieces of metal than smaller particles. The size of the particles will be an average size mostly, since this is a difficult factor to control (within limits) but the deviation of this average is what makes a stone of high quality or not. A large deviation from the average means the quality is low and this will have the effect of the abrasive seeming to be of a larger particle size, as the larger particles have a larger effect on the abrasion process.
The shape of the abrasive is also important. Particles which are angular will be more agressive and faster cutters than rounded particles. Sharp and angular corners are better and faster metal rippers than rounded and soft shapes. This is a characteristic that differs for natural occuring stones, waterstones, ceramics and diamonds. This is also one of the criteria that can play a role in your selection of sharpening tools.
The hardness of the abrasive, most often expressed in the Mohs scale (there are others), is important because there must be a hardness difference between the abrasive and the thing it is abrading.
The new Mohs scale of mineral hardness rates diamond at 15 whereas the old one (mostly used) rates diamond at 10. Talc is rated at 1. It's all about resistance to scratching. Steel is rated between 4 and 8, dependent on the steel properties and the hardening of it. A material that scratches more easily than another (lower Mohs value) can be scratched/abraded by that other material. That is the whole principle as to why sharpening and the longevity of the sharpening medium works. More information can be found here: http://en.wikipedia.org/wiki/Mohs_scale_of_mineral_hardness
The Mohs scale is not a linear scale and not consistent but provides an order in which we can place materials. Other scales exist for specific types of hardness measured, for us knife nuts the Rockwel Scale is also a thing that is well known (C variety: HRc, see http://en.wikipedia.org/wiki/Rockwell_scale)
Toughness is also a part of the equation. Particles need to be able to withstand shock or they can break in the process of sharpening. This will reduce the particle size, lessening the effect of the abrasive (making it in essence a finer abrasive). Toughness, or the lack thereof, can influence the effective lifetime of the abrasive.
There are two more factors that are not an intrinsic property of the abrasive material itself.
The bond between the abrasive particles. Particles adhere to each other or to a medium (like diamond in nickel) that keeps them in place. If the bond is too strong, the surface will become smooth over time (because of toughness and fracturing occuring) and abrasion rate will suffer from this. If particles do not adhere well, the abrasives will be ripped out and the stone will wear and lose shape. This is what happens to natural stones and why they need to be lapped. So lapping is a process that is both used to keep stones in shape with a bond that is too strong (ceramic, see http://en.wikipedia.org/wiki/Ceramic) and for stones with a bond that is not strong enough (waterstones, to get the stones level/flat). Diamond stones are embedded in nickel in a thin coating. Therefore, when pressing down with metal on diamond stones, the diamond abrasive particles can be ripped from the nickel medium which is essentially a weak bonding agent. Since it is only a thin layer of diamond, they can be easily ruined by using too much pressure. Done right, the diamond surface can last a long time.
The distribution density of abrasives might be considered too since this will effect the speed and ease of sharpening. As an example, one abrasive particle on a piece of glass will take you a loooong time to get something sharp. On the other hand, a lot of abrasive particles together have a pronounced effect on the speed.
All these factors come together in different materials that can be used for a sharpening tool. But materials are not the factor of a good abrasive, they are the medium that contain a useful mix of the properties mentioned above.
What materials are often used?
Different materials are used for different purposes. When going through the sharpening process there are multiple stages you can go through and different materials will be used. Grinding, polishing, sharpening and lapping are terms that define stages. Grinding is the bulk removal of metal and creating the shape and setting the edge, sharpening is what I consider the overall process, polishing is extremely refining the edge and lapping is for flatness. You can look up more about these processes here: http://en.wikipedia.org/wiki/Metalworking
Natural occuring materials were the first to be used in sharpening and are all crystals with some useful material properties as described above.
Quartz crystal is 7 on the old Mohs scale and is about as hard as hard steel. It is not sufficient for modern super steels which have higher hardness and crazy compositions. It is used in sandstones and comes in all sizes and often bonded because of a natural proces involving calcite.
Novaculite crystal (http://en.wikipedia.org/wiki/Novaculite) is found in the arkansas stones. The particles are highly regular in shape.
Aluminium Oxide is an important sharpening material.
When mixed/contaminated withabout 25% Iron Oxide and some small quantities of other materials, it is called emery.
Corundum is almost pure Aluminium Oxide. It is a better medium than emery. Problem with the natural materials emery and Corundum is that is does not have very good bonding properties.
Artifically created materials were developed which made better sharpening possible
The process of vitrification (http://en.wikipedia.org/wiki/Glass_transition) and the use of it for making a bonding agent is what made Norton a big player in the sharpening industry.
Silicon carbide (carborundum: http://en.wikipedia.org/wiki/Silicon_carbide), with an old mohs hardness of 9 to 9.5, was developed in 1891 and artificial corondum (pure aluminum oxide: http://en.wikipedia.org/wiki/Corundum), with a hardness of about 8, in 1897. Both were better sharpening materials than the available. For Aluminium Oxide, the process of crystallization could be controlled, thereby making it possible to create it in different particle sizes, which was a factor in it's succes.
Diamond (http://en.wikipedia.org/wiki/Diamond) was cost prohibitive for a long time, but since it is one of the hardest materials (but not the hardest: http://en.wikipedia.org/wiki/Carbon_nanotube), 10 on Mohs, it is potentially the best scratcher of the whole lot. Expensice diamond dust was used, but commercial succes came with new processes like crystal growing diamonds by General Electric and explosive/pressure conversion of Carbon to Diamond crystals.
Crystal generation creates monocrystalline diamonds, which is generally accepted to be much better for sharpening than polycrystalline diamonds. Monocrystalline does not fracture as easily, just like natural diamond. Polycrystalline is ideal for lapping and polishing, since it breaks down in the process because of it's aggregate nature, creating a finer abrasive while using it. Monocrystalling is more expensive but has a longer life and better performance.
There are more abrasives, but they are more exotic/expensive in nature and probably not relevant for this discussion.
When polishing with small sized particles, we see some other abrasives being used.
Diamond particles in solution, either spray or paste, are also used with small particle sizes for polishing.
Chromium Oxide (Cr2O3, http://en.wikipedia.org/wiki/Chromium(III)_oxide), also know as green compound is one of the well known, cheap and excellent materials for polishing. It has a Mohs value of about 8 to 8.5.
In essence, diamond, Al2O3, Cr2O3 are the most important polishing compounds. There are more polishing compounds but maybe others can describe them (black compound etc.). They are not as important.
Others that are sometimes mentioned and also not so important are:
IronOxide (Fe2O3, http://en.wikipedia.org/wiki/Iron(III)_oxide), also know as red rouge and rust is a fine polishing compound but only suitable for soft metals like brass and optics
Cerium Oxide (CeO2, http://en.wikipedia.org/wiki/Cerium(IV)_oxide) is sometimes mentioned but is more often used on glass.
Tin Oxide (SnO, http://en.wikipedia.org/wiki/Tin(II)_oxide) is used on soft metals.
A bond, in the broad sense of the word, often used for using polishing compounds is wood and leather (strops: http://www.bladeforums.com/forums/showthread.php?t=770338&highlight=demo+how+to+build+strop). Also, the polishing compounds like Cr2O3 can be bought in multiple forms, like in a solution, paste, wax or dry form, giving you a choice in how you apply them on leather/wood etc.
Plain (high quality) leather is said to have an effect on refining an edge, because of the small polishing silicates contained in it (smaller than 0.1 micron) and because of the way it moves over an edge, but there is no consensus on this.
where are those materials used?
diamond can be soldered into place for example in wheel dressers, pressed into the substrate, but most familiar for us is nickel plating the diamonds.
These are found on different diamond benchstones and handstones.
Examples are the dmt brand with diafolds (handheld) and duosharp benchstones, all monocrystalline (http://www.dmtsharp.com/general/whydiamond.htm)
Japanese waterstones (http://en.wikipedia.org/wiki/Japanese_waterstones) , both natural and artificial and natural stones like belgian stones, arkansas stones etc are most often in the form of benchstones.
Grinding wheels are another place where we find aluminium oxide, silicon carbide and diamond, often embedded in different subtrates. Vitrified bonds, resinoid bonds, rubber bonds and metal bonds are available.
Ceramics are usded in a lot of forms, handheld, like the doublestuff by spyderco, dc-4 by fallkniven (diamond and ceramic), spyderco sharpmaker, benchstones etc. As described above, there is little wear on these stones and they can have different abrasive particle sizes. It is a very good alround medium and is mostly corundum and carborundum based.
Sandpaper is also a very good sharpening medium, using carborundum and corundum in different particle sizes
What abrasive material should you use for a specific steel and method?
Grinding is mostly done with corundum, carborundum and diamond. It is an agressive form of removing metal so particle sizes are large
For lapping silicon carbide and aluminum oxide are used (red rouge for softer stuff)
for polishing diamond and chromium oxide are used on strops, but also very fine ceramic stones (spyderco UF etc) or very fine waterstones (japanese 8k+ stones)
In general, the harder the steel, the harder the abrasive needs to be because of a needed hardness differential. The faster you want to sharpen, the more agressive the cutter needs to be or the particles need to have a better contact with the knife (a reason that japanese waterstones are effective is because they wear, exposing fresh abrasives). The more polish you want, the finer the abrasive you need.
Diamond is sometimes preferred because it is hard and agressively shaped, more suited for modern steels.
Machining is preferred by some because it is fast and an easy way to expose a lot of particles in a short time. Since the wheels turn fast, the knife comes into contact with a lot of abrasives, since a wheel can essentially be regarded as a very long benchstone over which the knife travels very fast. Of course, this comes at the cost of more metal removal and less possibilities of fine tuning your sharpening process.
when talking about sharpening there is always a need to classify what the abrasives on the sharpening medium is so we have a way of comparing the different sharpening tools by different manufacturers out there.
In this post I will explain what abrasives are, what makes them a good abrasive, where you should use them and how we should describe them.
what are the factors for a good abrasive?
Particle size or particle size distribution (the average size) is an important part of the equation to get an edge that is worth calling sharp. It is important for the working speed of the abrasive and for the amount of metal that will be removed (at the scale of the abrasive). Larger particles will remove larger pieces of metal than smaller particles. The size of the particles will be an average size mostly, since this is a difficult factor to control (within limits) but the deviation of this average is what makes a stone of high quality or not. A large deviation from the average means the quality is low and this will have the effect of the abrasive seeming to be of a larger particle size, as the larger particles have a larger effect on the abrasion process.
The shape of the abrasive is also important. Particles which are angular will be more agressive and faster cutters than rounded particles. Sharp and angular corners are better and faster metal rippers than rounded and soft shapes. This is a characteristic that differs for natural occuring stones, waterstones, ceramics and diamonds. This is also one of the criteria that can play a role in your selection of sharpening tools.
The hardness of the abrasive, most often expressed in the Mohs scale (there are others), is important because there must be a hardness difference between the abrasive and the thing it is abrading.
The new Mohs scale of mineral hardness rates diamond at 15 whereas the old one (mostly used) rates diamond at 10. Talc is rated at 1. It's all about resistance to scratching. Steel is rated between 4 and 8, dependent on the steel properties and the hardening of it. A material that scratches more easily than another (lower Mohs value) can be scratched/abraded by that other material. That is the whole principle as to why sharpening and the longevity of the sharpening medium works. More information can be found here: http://en.wikipedia.org/wiki/Mohs_scale_of_mineral_hardness
The Mohs scale is not a linear scale and not consistent but provides an order in which we can place materials. Other scales exist for specific types of hardness measured, for us knife nuts the Rockwel Scale is also a thing that is well known (C variety: HRc, see http://en.wikipedia.org/wiki/Rockwell_scale)
Toughness is also a part of the equation. Particles need to be able to withstand shock or they can break in the process of sharpening. This will reduce the particle size, lessening the effect of the abrasive (making it in essence a finer abrasive). Toughness, or the lack thereof, can influence the effective lifetime of the abrasive.
There are two more factors that are not an intrinsic property of the abrasive material itself.
The bond between the abrasive particles. Particles adhere to each other or to a medium (like diamond in nickel) that keeps them in place. If the bond is too strong, the surface will become smooth over time (because of toughness and fracturing occuring) and abrasion rate will suffer from this. If particles do not adhere well, the abrasives will be ripped out and the stone will wear and lose shape. This is what happens to natural stones and why they need to be lapped. So lapping is a process that is both used to keep stones in shape with a bond that is too strong (ceramic, see http://en.wikipedia.org/wiki/Ceramic) and for stones with a bond that is not strong enough (waterstones, to get the stones level/flat). Diamond stones are embedded in nickel in a thin coating. Therefore, when pressing down with metal on diamond stones, the diamond abrasive particles can be ripped from the nickel medium which is essentially a weak bonding agent. Since it is only a thin layer of diamond, they can be easily ruined by using too much pressure. Done right, the diamond surface can last a long time.
The distribution density of abrasives might be considered too since this will effect the speed and ease of sharpening. As an example, one abrasive particle on a piece of glass will take you a loooong time to get something sharp. On the other hand, a lot of abrasive particles together have a pronounced effect on the speed.
All these factors come together in different materials that can be used for a sharpening tool. But materials are not the factor of a good abrasive, they are the medium that contain a useful mix of the properties mentioned above.
What materials are often used?
Different materials are used for different purposes. When going through the sharpening process there are multiple stages you can go through and different materials will be used. Grinding, polishing, sharpening and lapping are terms that define stages. Grinding is the bulk removal of metal and creating the shape and setting the edge, sharpening is what I consider the overall process, polishing is extremely refining the edge and lapping is for flatness. You can look up more about these processes here: http://en.wikipedia.org/wiki/Metalworking
Natural occuring materials were the first to be used in sharpening and are all crystals with some useful material properties as described above.
Quartz crystal is 7 on the old Mohs scale and is about as hard as hard steel. It is not sufficient for modern super steels which have higher hardness and crazy compositions. It is used in sandstones and comes in all sizes and often bonded because of a natural proces involving calcite.
Novaculite crystal (http://en.wikipedia.org/wiki/Novaculite) is found in the arkansas stones. The particles are highly regular in shape.
Aluminium Oxide is an important sharpening material.
When mixed/contaminated withabout 25% Iron Oxide and some small quantities of other materials, it is called emery.
Corundum is almost pure Aluminium Oxide. It is a better medium than emery. Problem with the natural materials emery and Corundum is that is does not have very good bonding properties.
Artifically created materials were developed which made better sharpening possible
The process of vitrification (http://en.wikipedia.org/wiki/Glass_transition) and the use of it for making a bonding agent is what made Norton a big player in the sharpening industry.
Silicon carbide (carborundum: http://en.wikipedia.org/wiki/Silicon_carbide), with an old mohs hardness of 9 to 9.5, was developed in 1891 and artificial corondum (pure aluminum oxide: http://en.wikipedia.org/wiki/Corundum), with a hardness of about 8, in 1897. Both were better sharpening materials than the available. For Aluminium Oxide, the process of crystallization could be controlled, thereby making it possible to create it in different particle sizes, which was a factor in it's succes.
Diamond (http://en.wikipedia.org/wiki/Diamond) was cost prohibitive for a long time, but since it is one of the hardest materials (but not the hardest: http://en.wikipedia.org/wiki/Carbon_nanotube), 10 on Mohs, it is potentially the best scratcher of the whole lot. Expensice diamond dust was used, but commercial succes came with new processes like crystal growing diamonds by General Electric and explosive/pressure conversion of Carbon to Diamond crystals.
Crystal generation creates monocrystalline diamonds, which is generally accepted to be much better for sharpening than polycrystalline diamonds. Monocrystalline does not fracture as easily, just like natural diamond. Polycrystalline is ideal for lapping and polishing, since it breaks down in the process because of it's aggregate nature, creating a finer abrasive while using it. Monocrystalling is more expensive but has a longer life and better performance.
There are more abrasives, but they are more exotic/expensive in nature and probably not relevant for this discussion.
When polishing with small sized particles, we see some other abrasives being used.
Diamond particles in solution, either spray or paste, are also used with small particle sizes for polishing.
Chromium Oxide (Cr2O3, http://en.wikipedia.org/wiki/Chromium(III)_oxide), also know as green compound is one of the well known, cheap and excellent materials for polishing. It has a Mohs value of about 8 to 8.5.
In essence, diamond, Al2O3, Cr2O3 are the most important polishing compounds. There are more polishing compounds but maybe others can describe them (black compound etc.). They are not as important.
Others that are sometimes mentioned and also not so important are:
IronOxide (Fe2O3, http://en.wikipedia.org/wiki/Iron(III)_oxide), also know as red rouge and rust is a fine polishing compound but only suitable for soft metals like brass and optics
Cerium Oxide (CeO2, http://en.wikipedia.org/wiki/Cerium(IV)_oxide) is sometimes mentioned but is more often used on glass.
Tin Oxide (SnO, http://en.wikipedia.org/wiki/Tin(II)_oxide) is used on soft metals.
A bond, in the broad sense of the word, often used for using polishing compounds is wood and leather (strops: http://www.bladeforums.com/forums/showthread.php?t=770338&highlight=demo+how+to+build+strop). Also, the polishing compounds like Cr2O3 can be bought in multiple forms, like in a solution, paste, wax or dry form, giving you a choice in how you apply them on leather/wood etc.
Plain (high quality) leather is said to have an effect on refining an edge, because of the small polishing silicates contained in it (smaller than 0.1 micron) and because of the way it moves over an edge, but there is no consensus on this.
where are those materials used?
diamond can be soldered into place for example in wheel dressers, pressed into the substrate, but most familiar for us is nickel plating the diamonds.
These are found on different diamond benchstones and handstones.
Examples are the dmt brand with diafolds (handheld) and duosharp benchstones, all monocrystalline (http://www.dmtsharp.com/general/whydiamond.htm)
Japanese waterstones (http://en.wikipedia.org/wiki/Japanese_waterstones) , both natural and artificial and natural stones like belgian stones, arkansas stones etc are most often in the form of benchstones.
Grinding wheels are another place where we find aluminium oxide, silicon carbide and diamond, often embedded in different subtrates. Vitrified bonds, resinoid bonds, rubber bonds and metal bonds are available.
Ceramics are usded in a lot of forms, handheld, like the doublestuff by spyderco, dc-4 by fallkniven (diamond and ceramic), spyderco sharpmaker, benchstones etc. As described above, there is little wear on these stones and they can have different abrasive particle sizes. It is a very good alround medium and is mostly corundum and carborundum based.
Sandpaper is also a very good sharpening medium, using carborundum and corundum in different particle sizes
What abrasive material should you use for a specific steel and method?
Grinding is mostly done with corundum, carborundum and diamond. It is an agressive form of removing metal so particle sizes are large
For lapping silicon carbide and aluminum oxide are used (red rouge for softer stuff)
for polishing diamond and chromium oxide are used on strops, but also very fine ceramic stones (spyderco UF etc) or very fine waterstones (japanese 8k+ stones)
In general, the harder the steel, the harder the abrasive needs to be because of a needed hardness differential. The faster you want to sharpen, the more agressive the cutter needs to be or the particles need to have a better contact with the knife (a reason that japanese waterstones are effective is because they wear, exposing fresh abrasives). The more polish you want, the finer the abrasive you need.
Diamond is sometimes preferred because it is hard and agressively shaped, more suited for modern steels.
Machining is preferred by some because it is fast and an easy way to expose a lot of particles in a short time. Since the wheels turn fast, the knife comes into contact with a lot of abrasives, since a wheel can essentially be regarded as a very long benchstone over which the knife travels very fast. Of course, this comes at the cost of more metal removal and less possibilities of fine tuning your sharpening process.
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:thumbup:
. I've seen the effects of just stropping my Cara Cara on my belt, going from hair shaving sharp to hair whittling sharp in less than 100 strokes. Maybe that little bit of burr debris left on the edge is getting cleaned off. Maybe there is some dirt or other contaminant stuck to the edge that the leather removes.
but a nice read imo