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ultimate strength

Maximum conventional stress (tensile, compressive or shear) that a material can withstand.

ultrasonic cleaning

Method of cleaning metal or plastic parts by immersing them in an aqueous or solvent-based cleaning solution and imposing ultrasound energy on the bath to enhance cleaning by creating cavitation conditions at the part surface, which imparts a strong scouring action to remove tenacious soils.

ultrasonic machining

Material-removal operation in which an abrasive slurry flows between a tool, vibrating at a high frequency, and a workpiece.

ultrasonic testing

Nonconductive test applied to sound-conductive materials having elastic properties for the purpose of locating inhomogeneities or structural discontinuities within a material by means of an ultrasonic beam.


In numerical-control applications, a cut shorter than the programmed cut resulting after a command change in direction. Also a condition in generated gear teeth when any part of the fillet curve lies inside of a line drawn tangent to the working profile at its point of juncture with the fillet. Undercut may be deliberately introduced to facilitate finishing operations, as in preshaving.


Tendency of a numerical-control/computer-numerical-control machine to round off the corners of a programmed path because of servo lag or backlash, or because mechanical systems cannot react quickly to programmed instructions, especially when the machine is cold.

undulations per revolution (UPR)

Undulations per revolution, or the number of waves on a workpiece, is a reference to the cutoff frequency of a workpiece.

universal head

Facilitates setups on a tool and cutter grinder by allowing the grinding head to rotate away from the work area, leaving table alignment undisturbed. Also called a swivel attachment.

universal milling attachment

Mounts on a horizontal mill, permitting the spindle to be set at almost any angle.

universal milling machine

Horizontal mill equipped with a table that swivels, with respect to the saddle, allowing angular surfaces to be cut without changing the workpiece’s position.

universal spiral-milling attachment.

On a universal mill, permits milling helixes with a helix angle greater than 45°. Mills gears, screw threads, worms, twist drills, spiral-milling cutters and other helical shapes. Mounted to a plain milling machine equipped with a dividing head, it permits the mill to handle work that otherwise would require a universal mill.