EDM Nano Notches

Microscope

That’s Really Small!

PH Tool has been at the forefront of EDM notching technology for nondestructive testing for decades. As inspection methods have become more sensitive, we have continuously pushed EDM processes forward to create smaller, more controlled, and more repeatable artificial reflectors for NDT calibration and qualification.

In the course of this development work, PH Tool coined the term “Nano Notch” to describe a class of EDM notches intentionally produced at the extreme lower limits of achievable notch width. What began as an internal distinction for a specialized manufacturing approach has since become a commonly used term within the NDT community.

 

Purpose-Built for Extreme Sensitivity

A Nano Notch is not simply a small EDM notch. It is a deliberately engineered reflector designed to be as narrow as physically practical at the notch opening, created specifically for the most demanding NDT applications.

Nano Notches exist to serve inspection scenarios where conventional EDM notches are no longer sufficient, particularly in high-sensitivity eddy current testing (ET) and penetrant testing (PT) applications where difficult visual detectability is desired. They are specialty features, produced intentionally at the edge of what is manufacturable, and are not recommended for most standard NDT needs.

 

What Defines a Nano Notch? 

A Nano Notch is defined by how it is made, not just by a target dimension.

Most EDM notches are produced using graphite electrodes, which are ideal for general-purpose notch manufacturing. However, graphite has a practical lower limit. It cannot be reliably ground thinner than approximately 0.002" (0.05mm), which results in final notch widths of about 0.003" (0.075mm) and wider once EDM overburn is accounted for.

To cross below that threshold, PH Tool switches electrode material entirely.

Nano Notches are produced using metal foil electrodes, rather than graphite. Metal foils are available in thicknesses below the grindable graphite limit, allowing us to produce notch openings in the 0.002" range and, in limited cases, slightly under.

This change in electrode material is what makes a Nano a Nano.

 

A Note on Minimum Width

Under ideal laboratory conditions, PH Tool has successfully produced Nano Notches with a measured opening of approximately 0.0006" (0.015mm). While an impressive technical achievement, this should not be considered the norm. Nano Notches are specified and produced with manufacturability, repeatability, and inspection relevance in mind. Customers should not design applications around sub-0.001" targets unless the inspection truly requires it and the limitations are fully understood.

 

Depth vs. Width: The Core Tradeoff

All EDM notches are governed by a fundamental tradeoff between depth and width, and Nano Notches are no exception. Because metal foil electrodes are extremely thin and fragile, Nano Notches are significantly limited in depth.

Typical capabilities for Nano’s:

  • Practical maximum depth: ~0.010"
  • Upper extreme, with increased width: ~0.015"
  • Typical achievable width: ~0.002" and slightly under
  • Deeper notches require proportionally wider opening

 

Length Limitations 

Nano Notches are also limited in length. Due to electrode stability and wear, Nano Notches are typically produced in lengths from:

  • 0.010" to 0.100"

Slightly longer notches are possible, but cost and risk of the notch “meandering” increase rapidly. Nano Notches should be reserved for applications where short, extremely fine reflectors are truly required.

 

Notch Shape and Cross-Section

Nano Notches can be produced in the same general shapes as conventional EDM notches, including:

  • Thumbnail (semi-circular) profiles with a 2:1 length-to-depth ratio
  • Semi-elliptical (elongated beyond 2:1) profiles

In cross-section, Nano Notches exhibit:

  • Parallel sidewalls at the opening and mid-section of the notch
  • A full-radius at the bottom, commonly described as a “U” shape

 

Cost and Practical Considerations

Producing Nano Notches is significantly more expensive than producing conventional EDM notches.

Reasons include:

  • Rapid electrode wear requiring frequent replacement
  • Increased setup and alignment time
  • Limited tolerance for vibration or access issues
  • Requirement for senior-level EDM machinists

For these reasons, Nano Notches should be considered specialty features for the most discerning inspection needs, not a default choice.

 

When Should You Consider a Nano Notch?

Nano Notches are best suited for:

  • Ultra-sensitive eddy current applications
  • Liquid penetrant demonstrations requiring difficult visual detectability
  • Research, development, or qualification programs pushing detection limits

They are not necessary for most standard UT or ET inspections and often provide no practical benefit over well-designed graphite EDM notches.

If you are unsure whether a Nano Notch is appropriate for your application, PH Tool strongly recommends discussing your inspection goals with our sales and engineering team before specifying notch dimensions.