Gear Cutting Overview 290

5-axis CNC machine

A multi-axis CNC machine that has two rotational axes and three linear axes. 5-axis CNC machines are the most common type of multi-axis machining center.

addendum

The distance between the top land of a gear tooth and the pitch circle. The addendum is above the pitch circle.

axis of rotation

An imaginary line around which an object spins. The axis of rotation is parallel to and runs through the center of a bearing's shaft.

backlash

The distance that a drive gear tooth is able to move without moving its driven gear. Backlash, or lost motion, is necessary for gear trains to operate properly.

bevel gears

A type of gear with conical teeth that are cut at an angle. Bevel gears are often used in angular gear trains.

blind holes

A hole that begins on one side of a workpiece and ends inside the workpiece. Blind holes only have one opening because they do not extend through the entire thickness of a workpiece.

broach

A multi-point cutting tool made of a series of progressively finer teeth. Broaches perform roughing and finishing cuts in one pass.

broaching

A cutting operation that uses a multi-point cutting tool with a series of progressively finer teeth. Broaching performs roughing and finishing at the same time.

burnishing

A finishing process in which a gear is meshed with a shaping tool very tightly, flattening any surface imperfections. Burnishing adds a gloss or polish to a part.

burrs

A rough edge remaining on material, such as metal, after it has been machined. Burrs may cause injury and interfere with the fitting of parts.

casting

A manufacturing process that involves pouring a liquid material into a hollow mold until the material cools into a solidified shape. Casting is used to produce gears and other manufacturing parts and products.

CNC gear milling

A cutting operation in which a CNC machine rotates a multi-point cutting tool against a gear blank to remove material. CNC gear milling operations can create many types of gears.

CNC lathe

A machine that uses computerized numerical data to control workpiece rotation and cutting tool movements for the machining of cylindrical parts. CNC lathes are precise and versatile.

CNC mill

A machine tool that uses computer numerical data to control cutting operations on flat, square, or rectangular workpieces. On a CNC mill, the cutting tool rotates against a workpiece that is fixed to a worktable.

computer numeric control machines

CNC machines. A machine controlled by a computer that runs special programs to manufacture a workpiece. Computer numeric control machines are very rigid and are capable of fast cutting speeds.

cutting

A machining process that uses a tool to remove material from a workpiece. Cutting processes are much more precise than forming methods for creating gears.

dedendum

The distance between the bottom land of the gear tooth and the pitch circle. The dedendum is below the pitch circle.

diametral pitch

The number of teeth given per inch of a gear's pitch diameter. Diametral pitch is the most common method of classifying gears used within the United States.

disc cutter

An end mill cutting tool that is shaped like a disc with teeth. Disc cutters are used to cut gears in gear milling.

end mills

A mill cutting tool used to machine grooves, slots, pockets, and contours into workpieces. End mills resemble drill bits with sharp teeth along their flutes.

external gears

Gears with teeth along the outer surface rather than their interior. External gears mesh with gears that make contact with its outer perimeter.

extrusion

A manufacturing process that pushes raw material through a die to create the shape of a part. Extrusion can be used to fabricate gears.

feeds

The rate at which the cutting tool and the workpiece move in relation to one another. Feed is typically a linear movement.

finishing

A final metal cutting pass that emphasizes tight tolerances and a smooth surface finish. Finishing cuts are performed in the final cutting passes of a part that has already been cut to its overall shape.

flutes

A straight or helical recessed feature on the periphery of a cutter. Flutes allow chips to flow away from the cut.

forging

A general category of metalworking processes that involves compressing bulk metal at elevated temperatures. Forging creates very strong parts but can also leave raised sections that must be smoothed out.

forming

A manufacturing process that forms parts by stretching, bending, or compressing metal or other material. Forming processes are not as precise as cutting methods for creating gears.

gear

A toothed round or cylindrical mechanical component that transmits power. Gears mesh with one another and can alter the speed, torque, or direction of mechanical energy.

gear blank

A piece of metal on which teeth will be cut to form a gear. Gear blanks can be cylindrical or shaped like rings or discs.

gear broach

A rod or cylindrical cutting tool with teeth along its surface used to cut internal teeth into a gear or a hole. Gear broaches are also called spline broaches.

gear shaper

A gear cutting tool that cuts and meshes with the gear being cut. Gear shapers cut with reciprocal motion while rotating along the surface of the gear blank.

gear shaping

A gear cutting operation in which a gear-shaped cutting tool is reciprocated into a rotating gear blank to form teeth. Gear shaping can create gears with high surface-finishes.

gear train

A system of gears used to transmit rotary motion from one part of a mechanical system to another. Gear trains contain two or more meshing gears.

grinding

A finishing process that uses an abrasive tool to remove material from a workpiece surface and achieve highly accurate measurements. Grinding operations commonly use abrasive grains bonded into a wheel shape.

grooves

A channel cut into a cylindrical workpiece. Grooves mesh with teeth in gears.

helical broaching

A broaching operation in which a broach with rows of teeth winding around it cuts through a workpiece while the broach rotates. Helical broaching creates helical gears.

helical gears

A type of gear with slanted teeth. Helical gears, also called crossed gears or screw gears, are quieter than spur gears, but they are more expensive.

herringbone gears

A type of helical gear that has angled teeth in the shape of the letter "V". Herringbone gears can take on greater loads than other gears but are expensive to manufacture.

hob

A cylindrical cutting tool with teeth around its circumference. Hobs are used in gear hobbing to cut multiple teeth at once.

hobbing

A cutting operation that rotates a cylindrical cutting tool against a workpiece while feeding the tool toward it. Hobbing uses a multi-point cutting tool called a hob.

honing

A precision abrasion process in which a relatively small amount of material is removed from a surface by means of an abrasive. Honing is used to obtain a desired finish or produce extremely accurate features.

horizontal broaching machine

A broaching machine with a broach that is parallel to the ground. A horizontal broaching machine moves the broach along the internal or external surface of the gear blank.

hypoid gear

A type of bevel gear with angled, curved teeth that transmits motion between non-intersecting shafts. Hypoid gears have teeth that slide together when meshing, which produces less noise but greater friction and heat than other bevel gear types.

imperial system

A recognized system of measurement adopted by the United Kingdom, Canada, and other affiliated countries in 1824. The imperial system is still in use for some measurements such as speed, distance, and volume but has largely been replaced with the metric system since 1965.

indexable inserts

A cutting bit that has multiple cutting edges. Indexable inserts can be replaced or changed to a new cutting edge after excessive wear or damage.

internal gears

Gears with teeth along their inner surface rather than their exterior. Internal gears are often part of a planetary gear train.

Intersecting axes

The imaginary centerlines of two or more objects that cross one another. Intersecting axes are used in gear hobbing and other cutting processes.

involute curve

A curved line that gradually becomes more distant from a center point. An involute curve, or involute, can be traced by a point on a taut string as it unwinds from a cylinder.

involute gears

A gear that is designed with an involute tooth profile. Involute gears are the most common gears used because they transmit motion uniformly.

lapping

A finishing process that uses a lap plate and abrasive compounds to bring surfaces to the desired dimensions and surface finish. Lapping uses a fine abrasive to grind away small amounts of material from a workpiece surface, resulting in very flat surfaces.

lapping plate

A tool that fits snugly against a workpiece while abrasive material is poured or sprayed between them. Lapping plates in gear lapping resemble gears.

machining center

An advanced CNC machine that can perform multiple machining operations at the same location with a variety of tools. Machining centers include multi-axis CNC machines.

mechanical energy

Energy used to perform work through the physical interaction and motion of tools or machine components. Mechanical energy can be produced in a number of ways.

mesh

The act of interlocking with another object. Gears are designed to mesh with one another in order to transmit mechanical energy.

metric system

A standard system of measurement based on the gram, liter, and meter. Metric system measurements are widely recognized as standard internationally.

mill

A multi-point cutting tool that is used to remove metal from the surface of a workpiece. Mills are used to cut materials to the near net-shape of a final part.

module

The distance along a gear's pitch circle, measured in millimeters, for each gear tooth. Module is used to metric gears.

parallel

A pair of lines that are equidistant from each other at all points along their length. Parallel lines never intersect with each other.

pinion

A circular gear used in a rack and pinion system to produce linear motion. As the pinion turns, the flat rack slides in a linear direction.

pitch circle

An imaginary circle on a gear that divides the gear teeth into top lands and bottom lands. Pitch circles of two meshing gears contact each other at the pitch point.

pitch diameter

The diameter of an imaginary cylinder that passes through the thread form in such a way that it intersects the thread groove and the thread ridge equally. A gear's pitch diameter can be determined by measuring from the top of one gear tooth to the bottom of the opposite gear tooth.

pitch point

The point at which the pitch circles of two gears contact each other. Involute gears with connecting pitch points produce uniform motion.

planetary gear train

A gear train that consists of one or more outer gears rotating around a central gear. Planetary gear trains are also known as epicyclic gear trains.

pot broaching

A gear cutting method in which multiple broaches are placed in a ring around the inside diameter of a cylindrical toolholder. Pot broaching allows the entire external surface of a spur gear to be cut at once.

rack

A flat bar with teeth used in a rack and pinion system to produce linear motion. Racks slide in a linear direction as circular pinions turn against them.

rack and pinion

A gear pair that is used to convert rotary motion into linear motion. A rack and pinion consists of a circular gear, or pinion, that meshes with a flat-toothed bar, or rack.

reciprocating

Moving repeatedly back-and-forth or up-and-down. Reciprocating motion is linear.

rotary broaching

A broaching operation in which a broach moves through a workpiece while rotating with a slight wobble. Rotary broaching, also called wobble broaching, is performed on common machine tools such as lathes, mills, or drill presses.

roughing

A metal-cutting operation which removes a large amount of material. Roughing operations define the overall part shape.

setup

The process of arranging tooling and fixturing on a manufacturing machine. One of the most important aspects of multi-axis machine setup is choosing the correct workholding devices.

shaving

A finishing process that uses a cutting tool to scrape off thin pieces of material. Shaving improves the surface finish and makes fine adjustments on gear teeth.

skiving

A cutting operation that rotates a cutting tool shaped like a helical gear against a rotating workpiece at a 15°-45° angle. Skiving has only been possible with the develpment of 5-axis CNC machines.

spline broach

A rod or cylindrical cutting tool with teeth along its surface used to cut internal teeth into a gear or a hole. Spline broaches are also called gear broaches.

spur gears

A type of gear that has straight, flat-topped teeth set parallel to the axis. Spur gears are the most common type of gears used in manufacturing.

teeth

Similarly shaped protrusions from an object. The teeth on a gear transfer motion from one gear to another by meshing together.

tolerances

An acceptable deviation from a desired dimension that still meets part specifications. Tolerances indicate the allowable difference between a physical feature and its intended design.

toolholder

A device used to hold a cutting tool in place during machining. A toolholder can be a range of devices, including a milling cutter and a spindle.

tooth profile

The basic shape of a gear tooth cross section. The most common gear tooth profile is the involute profile.

torque

A force that produces rotation. Gears can transmit high levels of torque.

vertical broaching machine

A broaching machine with a broach that is perpendicular to the ground. A vertical broaching machine moves the broach along the internal or external surface of the gear blank.

wobble broaching

A broaching operation in which a broach moves through a workpiece while rotating with a slight wobble. Wobble broaching, also called rotary broaching, is performed on common machine tools such as lathes, mills, or drill presses.

workpiece

A part that is in the process of being machined. Workpieces can be subject to gear cutting or gear forming processes to create gears.

worm

A screw-like shaft with teeth that mesh with the teeth of a worm gear to transmit motion. Worms usually push a worm gear in a worm gear set.

worm gear

A gear with teeth that mesh with the screw-like threads of a shaft, called a worm, to transmit motion. Worm gears are usually a type of spur gear.

worm gear sets

A worm gear used in combination with a worm. Worm gear sets are used to transmit power between nonintersecting shafts at right angles to one another.