When figuring out if you should use diamond or CBN for your machine needs, determine what you are trying to accomplish. Think about the workpiece and what it’s made from. Think about what kind of removal rate you need. You may even want to think about what kind of tolerances you have on the piece. Answering some of these questions will guide your decision and make it easier to find the right abrasive for the job.

What Is CBN?

Boron nitride is a chemically and thermally heat resistant compound material made by combining boron and nitrogen—the chemical formula BN. It occurs in many crystalline forms that have different properties. In one form, BN shares many properties with graphite and has applications as a lubricant or additive for cosmetics. In the cubic version, cubic boron nitride (or CBN), it has similar properties to diamond but with superior chemical and thermal stability. CBN is a man-made material that is ideal for cutting and grinding super-hardened steel.

What Is Diamond?

Everyone knows what diamonds are; they are shiny and sparkly and loved by people around the world for a variety of reasons. Diamond is a naturally occurring mineral that is the hardest known material on Earth. At first, many believed only men and machines could extract diamond from the ground. However, science has a way of catching up to nature, and by the 1950s, scientists created synthetic, man-made diamonds in labs. Beyond its use as a precious jewel for decoration, the diamond has industrial applications such as grinding and cutting. Diamond, as a cutting tool, can cut non-metallic materials such as granite, gorilla glass, concrete, and ceramic tiles. Used in a CNC milling machine, a diamond-tipped contour tool can machine just about anything.

So, Which One Should You Use?

The answer is clear. If you need to cut a super hard metal like steel, then use a CBN tool. The higher thermal conductivity better suits cutting steel—there is less chance of burning or damaging the workpiece. If you want to cut tempered glass, concrete, granite or non-metallics, use diamond. A  diamond drill bit for granite countertops or hard stone is the best choice.