Hard Turning 315

air passes

A cut on a lathe during which there is no depth of cut on an infeed. No cutting occurs during air passes, or skim passes, which can result in rubbing.

alternating flank infeed

An infeed method in which the leading thread flank and the trailing thread flank are alternated on each pass of the threading tool. On alternating passes, the direction of infeed switches between being parallel to the leading thread flank and being parallel to the trailing thread flank.

center height

A variable that determines where the tool approaches the workpiece. Ideally, the center height should be set so the tool approaches the workpiece at the same level as the center of the chuck and part.

ceramic

A hard, brittle material that can withstand high temperatures. Ceramic cutting tools require high cutting speeds and rigid machinery.

cermet

Any cutting tool material consisting of ceramic particles in a metallic binder. Cemented carbide tools are a type of cermet.

chatter

The occasional vibration between a workpiece and a cutting tool. Chatter decreases machining productivity, negatively impacts surface quality, and increases tool wear. Chatter is often caused by insufficient rigidity.

continuous cut

A type of cut in which the cutting tool is continuously engaged in the workpiece throughout the duration of the operation.

cubic boron nitride

A type of cutting tool material offering a hardness that is second only to diamond. CBN tools are very effective at machining most steels and cast irons, but they are also very expensive.

ferrous

A metal that contains iron. Carbon steels are common ferrous metals.

finish dimension

The final shape of the part, characterized by tolerance that meets the specifications set forth in the part's design.

finish grinding

An abrasive process that improves the surface of the part. Finish grinding emphasizes tight tolerances and smooth surface finish.

flash point

The lowest temperature at which a liquid produces enough vapor to form an ignitable mixture. Liquids with low flash points pose the greatest danger.

gib

A pair of precisely measured, parallel tracks that support and guide the movement of machine tool components.

hard turning

A single-point machining process, conducted on a lathe, involving workpieces with a hardness above 45 Rc.

hardness

The tendency of a material to resist scratching, indentation, or penetration. Workpiece materials with increased hardness generate more heat and are more difficult to machine.

Hastelloy

A superalloy made predominantly of nickel and various percentages of other elements. Hastelloy is designed to withstand high-temperature and high-stress environments in which corrosion-resistance is paramount to performance.

Inconel

A superalloy made of nickel and chromium and designed to perform well in extreme environments. Inconel is oxidation and corrosion resistant and is very difficult to machine.

interrupted cut

A type of cut in which the cutting tool is alternately engaged and disengaged in the workpiece throughout the duration of the operation. Interrupted cuts combined with coolant can cause thermal shock.

length-to-diameter ratio

A numerical value describing the length of a cylindrical workpiece compared to its diameter. Higher length-to-diameter ratios indicate low rigidity.

machinability

The ability of a metal to be cut and shaped by machine processes such as cutting, grinding, turning, or drilling. Machinability indicates the relative ease with which a metal can be machined.

modified flank infeed

An infeed method in which the tool is fed radially into the workpiece at a 2° to 5° angle from the thread flank. During a modified flank infeed, cutting occurs primarily on one flank, resulting in consistent forces and effective chip formation.

negative rake

A tool insert orientation characterized by the insert being ahead of an imaginary perpendicular line.

polymer style coolant

A coolant with a polymer additive that lowers its tendency to evaporate and corrode metal components.

positive rake

A tool insert orientation characterized by the insert being behind an imaginary perpendicular line.

radial infeed

An infeed method in which the tool is fed radially, or perpendicular to the workpiece centerline, during each pass.

Rc

Rockwell C. A hardness testing paradigm that measures the degree of penetration into a metal caused by a diamond or ball indenter applied under a fixed load. Tested materials are assigned a number indicating their relative hardness, or ability to resist indentation.

rigidity

The quality of a workpiece or setup characterized by being stiff and inflexible. A setup with good rigidity reduces vibration or wobble.

Rockwell C

Rc. A hardness testing paradigm that measures the degree of penetration into a metal caused by a diamond or ball indenter applied under a fixed load. Tested materials are assigned a number indicating their relative hardness, or ability to resist indentation.

rough grinding

Relatively aggressive grinding done to emphasize material removal with little regard for surface finish.

skim passes

A cut on a lathe during which there is no depth of cut on an infeed. No cutting occurs during skim passes, or air passes, which can result in rubbing.

Stellite

An alloy made of cobalt and chromium and designed to resist wear. Stellite is non-magnetic, corrosion resistant, and is extremely tough and hard.

surface speed

The rate at which the workpiece passes the cutting tool at the point of contact. Surface speed has the greatest effect on tool life.

tangential pressure

A force acting on the tool's rake face in the direction of the cutting velocity. Tangential cutting forces represent a resistance to workpiece rotation and constitute approximately 70% of the total cutting forces.

thermal shock

A potentially catastrophic stress in a material from sudden extreme changes in temperature. Thermal shock can cause a tool insert to break suddenly.

throughput

The rate of production for a process over a specific amount of time.

timing

The degree to which the top of a screw is flush with the top of the clamp on a toolholder.

titanium carbide

TiC. A material used to make carbide cutting tools that offers improved chemical stability and crater resistance.

torsional pressure

A force acting on a rotating workpiece as contact with the tool attempts to twist the workpiece against itself.

water-based coolant

A coolant with a high percentage of water content. Water-based coolants are not flammable and have additives to increase its boiling point.

white layer

A thin layer of hardened material caused by a dull insert that gives the false impression of a successful part until the surface fails. Hard turning often requires predicting the wearing of inserts so they can be changed before they cause the white layer.