Flat Bottom & Other Holes

PH Tool offers many different types of holes used in NDT today. The popular ones are listed below. If you don't find what you're looking for, call us and we'll be happy to discuss how it can be done. We employ both conventional machining (drilling) and non-conventional (EDM) in the hole-making process. The determining factors we consider in choosing a method are machinability of the workpiece, accessibility, hole diameter and depth.


Flat-Bottom holeFlat-Bottom hole

The flat-bottom hole (FBH) is machined to have a flat reflecting surface at the hole bottom. The hole bottom is typically parallel to the beam entry surface, but can be machined at other desired angles. Primarily used in Ultrasonic testing, with some application in Eddy Current testing, FBHs can be machined just about anywhere they are needed for a particular inspection. Available in diameters from .005".


Side-drilled holeSide-drilled hole

The side-drilled hole (SDH) is typically a drilled hole, the side wall of which is used as the reflecting surface. Unlike the FBH, the bottom of a SDH serves no purpose. SDHs are often drilled in pipe walls at specified locations from the diameter, e.g.: 1/4T, 1/2T, and 3/4T. They can be drilled either longitudinally or circumferentially to the axis of the pipe. They can also be machined in plate, bar or other products. Primary use is Ultrasonic testing. Available in diameters from .010".


Micro-sized holeMicro-sized hole

The micro-sized hole (MSH) is a small diameter hole used primarily in Liquid Penetrant inspection. Hole diameter is normally 0.004 to 0.005", and hole depth is 0.008 to 0.010". These micro-sized holes meet the requirements of the U.S. Navy's NSTR-99 Rev. 2 (Qualification Examination Requirements for Nondestructive Test Personnel). They can be machined in welded plate, pipe, bolts, or any test prop. Also available in diameters and depths other than stated above.


Concave Radius-bottom holeConcave Radius-bottom hole

The concave radius-bottom hole is machined with a concave radius at the hole bottom. Applications include ID pitting of tube or pipe for Eddy Current Inspection; and Liquid Penetrant test props. Available in diameters from 0.004".


Irregularly-shaped pitsIrregularly-shaped pits

These holes and pits are machined in irregular configurations, not described above. Includes star-shaped, square holes, hex holes, and realistic pits. EDM pit electrodes can be cast from real pits and used to reproduce actual pits very accurately. If you still haven't seen the hole you need, use your imagination... we'll figure out how to accomplish it.


Flat Bottom Drill

Flat Bottom holes drill images

A magnified comparison of a flat bottom drill (top) which was ground from a conical drill (bottom).


Watch our demo video about how Flat Bottom Holes are made.


This shows pits at 48X magnification.



Irregular Pit in turbine blade

This photograph shows a cast replica of an irregular pit machined by EDM into a turbine blade. Pit dimensions are .010” diameter x .020” deep. Any size and shape is possible.

irreg pit 2This shows pits at 192X magnification.



irregular pit



If you have further questions related to flat-bottom hole reference standards, then feel free to reach out to us

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