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When discussing advanced cutting materials, we usually mean CBN, PCD and ceramic. Many people avoid using these materials because they are significantly more expensive, typically costing between 4 and 40 times more per cutting edge relative to a standard carbide insert. A single PCD cutting edge can run $160, while a carbide edge costs just $4. Yet in certain applications, these tools deliver returns that overcome their price tags. This article examines when the investment makes sense and how to select the right solution for your turning operation.

About the author: Erez Speiser is the founder and developer of the Machining Doctor website, which reflects his 30 years of experience serving in management, engineering, production and marketing roles within the machining industry. Combining his extensive knowledge of the industry and web development skills, Erez founded the Machining Doctor website, a platform where he shares a wealth of expertise and insights to industry professionals. Contact Erez on LinkedIn.

What Makes These Materials Special

The defining characteristic of advanced cutting materials is hardness, which is significantly more than carbide. Carbide sits at 1,300 to 1,800 HV. Ceramic jumps to 2,100 to 2,400 HV, roughly 40% harder. CBN reaches 4,500 to 5,000 HV, while PCD tops out at 5,000 to 6,000 HV, making it the hardest cutting material available.

This hardness advantage enables machining of exotic or hardened materials that carbide cannot handle, unless you machine at drastically reduced speeds and can live with poor tool life. The question isn’t whether these materials perform better, but whether that performance justifies the cost in your specific application.

CBN: The Hardened Steel Solution

Cubic boron nitride is the second hardest material known, after diamond. At around $40 per cutting edge, it costs 10 times more than carbide, but its combination of hardness, hot-hardness and chemical stability creates unique capabilities.

Hardened steel: The practical limit for carbide is 45 HRC. CBN handles steel up to 70 HRC, which means operations that previously required an additional grinding operation after turning can be finished in one operation on the CNC lathe. In many cases CBN can eliminate the need to buy additional equipment or to outsource a job to a grinding subcontractor.

Cast iron and superalloys: Carbide inserts run well on cast iron and Inconel, but CBN can run three times faster (up to 5,000 sfm) on cast iron and as much as five times on Inconel. As you will see later in the article, ceramic is the more common choice for these materials, but CBN inserts are sometimes used for finishing operations when better surface finish and tight tolerance are critical.

An important thing to note is depth of cut limitations. You’re restricted by the brazed CBN tip size. Solid CBN inserts exist for heavier machining, but costs become astronomical, and these are reserved for specialized applications where no alternative exists.

Ceramic Inserts: The Economical Middle Ground

Made from aluminum oxide or silicon nitride, ceramic inserts sit between carbide and CBN at 2,100 to 2,500 HV. At $10 per cutting edge, they’re more affordable than CBN, and they deliver substantial performance gains.

For hardened steel in the 45 to 55 HRC range, ceramic provides an economical alternative to CBN. However, for hardness above 55 HRC, CBN is your only option.

In cast iron, ceramic inserts run six times faster than coated carbide, making them very popular in mass-production manufacturing lines, where productivity is critical.

The most popular use case for ceramic is machining nickel-based superalloys, like Inconel 718, where cutting speeds reach seven times those possible with carbide. Aerospace components are often large and take hours to complete. When a ceramic insert cuts cycle time from 8 hours to 2 hours, the higher insert cost becomes trivial compared to machine time savings.

PCD: Dominating Non-Ferrous Machining

Polycrystalline diamond represents the ultimate in cutting material hardness. Created by sintering diamond particles with a metal matrix under extreme temperature and pressure, PCD is 90% to 95% diamond with hardness near 6,000 HV.