Monocrystalline diamonds make the coating question “moot.”
Was asked a question “Why all the fuss about tool coatings? The base material and the tool geometry  do the work.”

Coatings can make the impossible possible.

We agree that the tool material and geometry are important determinants of success in production machining. See our original post here.  But tool coatings can play a critical role in assuring successful machining by

  • Significantly increasing tool life by minimizing wear;
  • Control built up edge (BUE);
  • Contol heat build up;
  • Increase the edge hardness.

To me, and I hope to you, ‘successful machining’ means  “more parts produced per day at lower cost per part.” Coatings help achieve this by increasing tool life (reducing tool cost component per part); by keeping machines running longer between changes (more parts per shift because more uptime per shift); and reducing variability of parts produced (BUE  and thermal variation requiring machine adjustments).
Advancing the idea from Diamond Coatings  (polycrystalline) to a Monocrsytalline Tool Insert, the folks at Paul Horn and  H10 worldwide  make the coating material into  the tool material- to make the impossible possible. The photo above shows an aluminum workpiece machined to a maximum surface deviation of Ra 0.010 μm; Rz 0.014 μm. It is an optical component machined from a single piece of aluminum, that I photographed at Paul Horn Technology Days last month.
Or how about this plastic workpiece- absolutely no tool marks or ‘frosting’:

Monocrystalline Diamond Coating Makes a Difference!

Polycrystalline diamond coatings are widely available. This monocrystalline diamond tooling was first shown to us by Horn USA at our 2010 National Technical Conference.  While diamonds are a non-starter for ferrous workpieces, they can be your key for  ‘brilliant machining’ on other workpiece materials such as aluminum, copper,  brass and bronze, nickel, precious metals, and  plastics like PVC, polycarbonate, acrylic.
But I guess it isn’t quite correct to call it a coating.

Mirror, Mirror from the cutoff...

In most shops there are three magic bullets that can make a job go better:

  • Tool Coatings
  • Tool Geometry
  • Tool Substrate (material)
    Are you guilty of magical thinking?

Magic bullet number 1- Coatings
Tool coatings are important technologies that help us get longer tool life, thus longer operating uptime and therefore more billable production (dollars) per day in our shops. But, just as cold medicine is not the cure for heart attacks, tool coatings are not always the solution for an underperforming job. On a job with interrupted cuts, the tool material- its strength and grain structure are often far more important than coating on the tool. But if the last problem that the shop had was cured with a new “super coating” you can bet that  that new coating will be first to be suggested on this newest problem at hand.
Magic Bullet Number 2- Geometry
Geometry is a critical component of every machining operation. Geometry is the determinant of power required, as well as strength of the tool edge and the setup. Geometry has an important role on surface finish, and in confined spaces (deep holes, parting off, grooving, etc.) the ability to control the chip with geometry alone is an important means of assuring success. While rake angles tend to be fairly typical for certain work-piece materials, there are situations where a change in geometry can solve the problem of chip clogging, rough finish, or poor tool life. Once a shop has “learned” that changing geometry can make a problem go away in a material, they tend to over generalize that lesson. While it is likely that the geometry change was effective because of the particulars of the operation, not just because of the work-piece material, changing angles jumps to the head of the line the next time a shop runs into difficulties, especially if it is the same material. Geometry and chip control is a crucial aspect of machining success, particularly in deep holes, grooves, bores and cutoffs, but it is not the only one.
Magic Bullet Number 3- Substrate and Material issues
What the tool (or work-piece) is made of is another area that can mean success or failure to a difficult job. The advent of micrograin carbides was an event celebrated by machine shop owners everywhere, and developments in this area continue to improve our bottom lines. The same too, for work piece materials. Once a shop finds out that supplier “A’s” material machines fine on a job, they immediately prefer it, often times without identifying which aspects of the provision of the material are aiding their production. Some suppliers have multiple process paths to make some items, and service centers often shop the world for price or delivery, bringing the full range of global variability to bear on your job. Consistency in supply is important, but it goes well beyond the name on the tag, to parameters of the processing and sourcing of the material itself.
It’s not a single magic bullet. For each workpiece material, feature to be produced, machine tool, there is an optimum combination of tool substrate, geometry, and coating to produce the part to print with a minimum of downtime and management hassle. Looking for a magical single solution is generally the wrong approach.