Will diamond tools produce a different finish quality?

The short answer is, no. Your question is difficult to reply to without qualifying what is meant by different. Polycrystalline diamond cutting tools have been evolving steadily since the material was developed in the U.S. in 1954. Most of the development and research, however, has been accomplished by European cutting tool manufacturers seeking a means to cut very difficult and abrasive materials. In fact, the very first outstanding success for diamond tools was cutting plastics and fiberglass materials used to manufacture skis.

At the onset in the development of diamond tools, the cutting and relief angles used were very shallow to provide a large wedge angle. This was intended to protect the leading edge of the tool knife from impact fracture. Diamond cutting tool knives are still the most expensive, and in many ways the most frail, material used for such a purpose.

Continued research and development over the years has revealed that the cutting angles and relieved features can be made similar to those for other knife materials, especially where the knives can be set at a shear angle or, better yet, in a spiral arrangement.

Polycrystalline diamond tools will never be considered all-purpose cutters. Even after 40years, most are still made-to-order. Each application must be considered carefully. However, if the machining process and material cut is appropriate, there are several advantages to diamond tools, not least of which is a considerable cost savings.

Finish quality isn't a problem if the tool is designed correctly for the material and machining process.

Are there any tool applications where high-speed steel is the superior knife material?

The short answer is yes. The word "superior" can have several definitions -- less costly, longer run times, or maybe better finish quality. Cutting tools have knives made of several materials, primarily high-speed steel, tungsten carbide, or polycrystalline diamond.

Without pursuing all of the physics, chemistry, and mechanics involved, each of the three primary tool knife materials have distinct advantages.

High-speed steel is at its best cutting solid wood materials, faulted or not, without glue lines. This is from the advantage of overall operating cost and finish quality.

HSS can be ground and honed to have a much sharper edge than most other knife materials. It's also more forgiving and less costly to replace or repair if loose, dense knots or mineral streaks are present in your wood. In many instances, HSS will outperform other knife materials when cutting woods with very low pH or with unusual moisture content or chemical compositions.

My own general rules for selecting a tool knife material are based on:

  1. How much of the machining process will be done each day, week, month, etc.
  2. The machining process itself. Are you using a circular saw, planer, moulder/shaper, or router?
  3. The physical, mechanical, and chemical properties of the material being cut or machined.

Selecting cutting tool knives is becoming more difficult. The rule is learn as much as possible.


 Tool Choice

Natural woods, without glue lines

 HSS, tungsten carbide, or patented alloy

Natural woods with glue lines

 Tungsten carbide or patented alloy

Man-made panel/solid material

 Tungsten carbide, diamond, or patented alloy

Polycarbonate hard surface

 Tungsten carbide or diamond materials

Thermoformed plastic materials

 Tungsten carbide or diamond

Nonferrous metals

 Tungsten carbide or patented alloy

Wood/mineral composite materials

 Tungsten carbide or patented alloy

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