EDM Notch Shapes

PH Tool™ is highly-specialized in producing artificial discontinuities known as electrical discharge machined (EDM) notches. EDM notches are typically produced from an otherwise acceptable production item supplied by the manufacturer of the part or the test lab performing the inspection. When selecting what type of EDM notch is right for your application, it is important to consider both the width and length cross-section of the notch. There are various geometries available that all have their purpose for testing applications. 


Options for Notch Width Cross-section:


Square Notch

Square Notch

This notch is also referred to as a “Buttress” notch and has parallel-sided walls and minimal corner radius at notch bottom. Typical of notches over 0.010” wide. Available in depths from 0.0001”; widths from 0.010”; and lengths from 0.005”.


U Notch


This notch has parallel-sided walls at the entry surface and a corner radius at notch bottom resembling a “U-shape”. Typical of notches under 0.010” wide. Available in depths from 0.0001”; widths from 0.003”; and lengths from 0.005”.


V Notch


This notch has angled side walls that meet at the notch bottom. Typical V-notch included angles (a) are 40°, 45°, 60°, 70°, 75° and 90°, with 60° being the most common. V-notch half-angle should complement beam angle for maximum response. Available in depths from 0.002”, and lengths from 0.020”.


Nano Notch

Nano Notch

The absolute narrowest notch available today. Available in widths from 0.0006”, depths from 0.0001”; lengths from 0.005” through 1.00”. Some depth limitations exist on ultra-narrow notches depending on configuration and alloy. Call Technical Sales to discuss possibilities.


Wire EDM Notch

Wire EDM Notch

This notch is made using a wire EDM machine instead of a traditional sinker EDM. Our state-of-the-art wire machines allow for extremely narrow notches (down to 0.003” wide) that can reach nearly unlimited depths. The limitation is on the length of the notch. The travelling wire on the machine must completely span the part so that new wire can be fed from the top nozzle down through the bottom nozzle. The result is a notch that breaks out the edges of the part. For this reason, the notch length is always the same as the width of the part.


Crack Like Notch

"Crack-Like" Notch

A variant on the wire EDM Notch. The Crack-Like Notch is made via wire EDM, and therefore must be open to the surface on at least two sides. The wire EDM is programmed to follow a “crack-like” path of the customer’s choosing. The feature can also be made wider to simulate a corrosion pattern. The options are nearly endless!


Stepped Notch

Stepped Notch

This unique notch type is typically used when burning to extreme depths, where a narrow reflecting surface is needed at the bottom of the notch. We start by removing the majority of material with a wide cavity, and then “step” the width of the notch down with a narrower electrode (or several) until the final depth is reached. This leaves the narrowest reflector at the bottom. It is a similar concept to using a counterbore when drilling a hole.  The larger opening at the top allows for more rapid material removal and efficient evacuation of debris from the cavity. 

Options for Notch Length Cross-section:


Rectangular Notch

Rectangular Notch

The most basic of the length cross-sections available. When viewing the length of this notch, it appears rectangular in profile. Width cross-section can be Square, U-shaped, V-shaped, or Nano.  


Semi Circular Notch

Semi-Circular notch (Thumbnail, 2:1 aspect Ratio)

When viewing the length of this notch, it appears as a perfect half-circle, twice as long along the surface as it is deep. Often used in eddy current testing applications. Available in depths from 0.0025”; widths from 0.003”; and lengths from 0.005”. Sometimes referred to as a “half-penny” notch.


 Semi Elliptical Notch2

Semi-Elliptical Notch (True Ellipse, >2:1 aspect ratio)

When viewing the length of this notch, it appears as a perfect half-ellipse, or oval. The aspect ratio for length to depth is always greater than 2:1 (wider than a perfect circle.) Common in eddy current or fatigue starter notch applications. Available in any depth; and widths from 0.003”.


Irregular Bottom Notch

Irregular-Bottom Notch

When viewed from the side, the length of this notch follows a contour of the customer’s choosing. The notch depth varies along the length in an attempt to simulate an actual crack or in-service condition. This type of notch is machined via sinker EDM using a custom-shaped electrode. Use your imagination!