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I am planning to move from conventional grinding wheels to super-abrasive grinding wheels. I am unable to decide the right type of super-abrasive wheel for my manufacturing operations (I am into knife manufacturing).

How do I select a the correct grinding wheel type for precision grinding of tool grade steels such as those used in knife manufacturing?

Specifically I would like to know what the differences are between resin bonded and vitrified CBN grinding wheel. I would also like to know which wheel can be used for precise and fine grinding applications.

Thankyou.

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Here is what you need to know when selecting a grinding wheel. My experience is in manufacturing research and I do not know much about the specifics of knife making, but there are some general rules you can look at when selecting a grinding wheel. Always check the specs provided by suppliers for specific information on the correct wheel to order from them.

TL;DR: for precision grinding/finishing of a stainless steel workpiece, you should use a cBN abrasive type, metal or vitrified bond type, small (fine) grain size, soft grade wheel.

Grinding wheel specification

In order to choose a grinding wheel you need to understand what the wheel markings mean. Superabrasive grinding wheels are often specified using the ANSI Standard B74.13-1977 marking system:

XX - B - 150 - P - YY - V - ZZ - 3

The parameters are, in order:

  • XX, Manufacturer's prefix: not important
  • B, Abrasive type: D = diamond, B = Cubic boron nitride (cBN)
  • 150, Grain size: 8 to 24 = Coarse, 30 to 60 = Medium, 70 to 180 = Fine, 220 to 600 = Very Fine
  • P, Wheel grade: Value from A to Z. A = soft, M = medium, Z = hard
  • YY, Concentration: Varies between manufacturers, check the datasheet for whatever company you are looking at.
  • V, Bond type: B = Resin, M = Metal, V = Vitrified
  • ZZ, Bond modification: Varies between manufacturers
  • 3, Depth of abrasive: Working depth of the abrasive in inches or mm, check the manufacturer's datasheet (unlike conventional wheels, subperabrasives are often only applied in a thin layer to the outside of a wheel rim because they are rather expensive).

The above was somewhat paraphrased from [1].

I will now comment in more detail on the parameters that you are interested in.

Bond types

The difference between resin bonded and vitrified bonded grinding wheels is the material used to bond the grains. Different bond types have different hardness, toughness and temperature resistance properties.

In general:

"[Vitrified bonds consist] chiefly of baked clay and ceramic materials. Most grinding wheels in common use are vitrified bonded wheels. They are strong and rigid, resistant to elevated temperatures, and relatively unaffected by water and oil that might be used in grinding fluids." [1]

"[Resinoid bonds consist] of various thermosetting resin materials, such as phenol-formaldehyde. They have very high strength and are used for rough grinding and cutoff operations." [1]

Vitrified bonds are better for precise finishing operations than resinoid bonds. I work in a manufacturing research lab and most of the wheels we use are vitrified bond grinding wheels, for the reasons stated above.

There is, however, another option. Often cBN and diamond superabrasive wheels use metallic bonds (usually bronze). Grains are attached in a very thin layer to the metal substrate with metal bonded wheels, which tends to save significant amounts of abrasive and therefore money.

Abrasive types

Good idea moving to superabrasives for your application. Good quality knives to my knowledge are made of tool grade stainless steels [2], and that's what cBN (cubic boron nitride) superabrasives are good for [1].

I've ground stainless steel with conventional aluminum oxide wheels. They work alright, but it takes a long time with lots of re-dressing of the wheel. Diamond superabrasive would also work, but would probably be overkill for your application. Silicon carbide can work for stainless steels but is not compatible with most other steels due to chemical reactions between the wheel and workpiece.

Other things you should note

For a precision grinding application, assuming that the abrasive you have chosen is compatible with the workpiece material, the most important parameter that you need to select is the grain size.

Small grit sizes produce better finishes, whereas larger grain sizes permit larger material removal rates. Thus, a choice must be made between these two objectives when selecting abrasive grain size. The selection of grit size also depends to some extent on the hardness of the work material. Harder work materials require smaller grain sizes to cut effectively, whereas softer materials require larger grit sizes. [1]

So because you are cutting a relatively hard material (tool grade stainless steel) and you want a fine surface finish you will want to select a small (fine) grain size. Note that grit/grain sizes are numbered "backwards" to the way you might expect: small grains have high grit numbers and large grains have small grit numbers.

You also want a soft wheel grade. Soft wheels are better for hard materials and low material removal rates than hard wheels. However, the tradeoff is that hard wheels are better for removing lots of material quickly (for a grinding process anyway).

[1] Mikell P. Groover, Fundamentals of Modern Manufacturing, 5th Ed.

[2] http://www.buckknives.com/about-knives/choosing-the-right-knife/#types-of-steel

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CBN grinding wheel provides you with great grinding ability : low grinding wheel wear, longer wheel life and good work material removal, etc.

You can opt of softer grade CBN grinding wheels with a fine abrasive grain size for your high precision application. I would suggest you to go for vitrified type bond for higher durability, reliability and high resistance to corrosion due to coolant used.

You can call up or meet up with any grinding wheel manufacturer/retailer near you and seek their help in selecting the best grinding wheel for your application. They know the best, and thats what they do for a living.

Hope this helps.

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I have some experience of knife making. I would say that you might also look at abrasive belts rather than wheels these give rather more flexibility in terms of both range of abrasives for different operations like grinding vs sharpening of hardened steel and also allow a greater range of grind profiles. eg with a wheel you are stuck with hollow grinds whereas a belt grinder allows for both hollow grinds of varying radius and flat grinds of any arbitrary angle.

certainly most professional knife makers I know of prefer belt grinders.

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