General Questions
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| What is diamond? |
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Diamond is composed of pure carbon atoms, arranged in a very special crystal orientation that gives it its unique physical properties. The key element that allows for the special crystal structure is the “sp3” bonding of the carbon atoms—and that is where sp3’s company name comes from. |
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| What materials are best suited to machining with diamond? |
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Abrasive non-metallic materials, non-ferrous metals, and abrasive non-ferrous metals. |
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| Why can’t you machine ferrous metals with diamond? |
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Diamond is unaffected by almost every other chemical or compound in nature. One exception is hot iron. The carbon atoms in diamond will dissolve into the iron, quickly eroding the diamond surface. Iron wheels are used for polishing natural diamond. That said, under certain conditions and with certain cooling substances, it is possible and even desirable to machine ferrous materials using diamond. Contact sp3 for details. |
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| How thick is the diamond on sp3 tools? |
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Thickness is tailored to the application, and can range from 5 to 50 microns. |
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| How do coating thicknesses in microns relate to inches? |
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1 micron is 1 millionth of a meter, or 0.00004 inch. A coating thickness of 10 microns is therefore 0.0004 inch; 40 microns is 0.0016 inch. |
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| How do you grow diamond? |
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The diamond coating is grown in a vacuum chamber using feed gases of hydrogen and methane. Usually the gases are fed into the chamber in a 50:1 mix, predominantly hydrogen. A very high temperature element in the chamber causes the deposition process to take place.
sp3 uses fine filaments energized to a temperature of approximately 2200°C. The high temperature breaks down the methane into carbon and hydrogen. The carbon atoms will nucleate and grow tiny crystals of diamond. In time these tiny diamond crystallites will grow into a continuous diamond film. |
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| How long does it take to coat a tool? |
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Diamond grows slowly, about 0.5 to 1.0 micron per hour. A typical reactor run to grow 40-micron films on inserts can take almost two days; most round tools are coated overnight.
Because of the slow diamond growth rate sp3 finds ways to maximize the number of tools that are coated in every reactor run. |
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| How many tools can be coated in a reactor? |
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The sp3 reactor provides a uniform diamond coating over an area of about a square foot. This enables coating 200 to 300 inserts at a time, or 65 to 100 round tools. |
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| Why are diamond-coated tools so expensive? |
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Primarily because of the slow growth rate of the diamond film—0.5 to 1.0 micron per hour. Another factor is pretreatment of the substrate to guarantee good adhesion. As pretreatment and deposition processes are further developed costs will drop, as they do in most maturing technologies. |
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| How do you make the diamond coating stick? |
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Left to itself, diamond has almost no chemical bond to cemented carbides. The trick is to pretreat the carbide surface, roughening it so the diamond can grow into the surface and attach itself through the mechanical interlocking of the carbide and the diamond. |
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| How sharp is the cutting edge on a diamond-coated tool? |
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The coating will naturally tend to round the edge somewhat. Sharpness is a function of the sharpness of the uncoated tool and the thickness of the film. Thin (10 micron) films over a dead sharp edge are still quite sharp. Thicker films, e.g., 40 microns, will approach an “A” hone in sharpness. |
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Custom Coating
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| What carbide grades can be coated? |
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This can’t be answered in just a few words. In general, typical C2 nonmicrograin carbides are the best candidates. For a complete list please contact Customer Service at 888-547-4156. |
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| Can sp3 coat micrograin carbides? |
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sp3 can coat down to about a 1 micron carbide grain size. If the carbide is too fine it does not respond to the preparation, which requires a rough surface for good adhesion. |
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| If I send sp3 a tool, can they coat it? |
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If it is in an approved carbide grade and the geometry within our limits we an coat it. Please contact Customer Service at 888-547-4156 with specific questions. |
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| If I send sp3 a tool in an acceptable grade for coating, how long will it take? |
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sp3 can typically turn around custom coating requests in about 10 working days. |
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| Can tools coated with other coatings such as TiC and TiN be coated with diamond? |
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Unfortunately not. sp3 needs a bare carbide tool of the proper grade to insure a successful bond between the diamond and the carbide. |
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| Can tools be diamond coated a second time? |
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sp3 does not coat tools that have already had a diamond coating for two reasons. The first is that the diamond deposition process alters the carbide at the surface, and the required surface preparation will be less predictable a second time.
The second reason is the uncertainty of the integrity of the ground edges. Often a tool is run until the diamond film is worn through in one or more spots. The carbide substrate will wear very quickly once the diamond is gone, leaving a notch or groove in one or more spots on the tool. These defects are difficult or impossible to remove with further grinding. |
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| Can HSS tools be coated? |
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During deposition the substrate temperature is about 850°C. High-speed steel will not survive these high temperatures. |
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| Can tools with brazed carbide tips be coated? |
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The normal deposition temperature is 850°C. Typical brazing will not survive these high temperatures. |
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| Can you braze diamond-coated tools? |
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This is feasible if the braze is done in a non-oxidizing atmosphere such as argon, and temperatures are kept as low as possible. However, one consideration is that the tool cannot be touched up or ground to size after brazing. You would be grinding a thin diamond film, and it would be very difficult to grind accurately without the possibility of breaking through the film. |
