Gear cutting
Encyclopedia
Gear cutting is the process of creating a gear
. The most common processes include hobbing, broaching, and machining; other processes include shaping
, forging
, extruding
, casting
, and powder metallurgy
. Gears are commonly made from metal
, plastic
, and wood
.
s, a vertical broach is used. It consists of a vertical rail that carries a single tooth cutter formed to create the tooth shape. A rotary table
and a Y axis are the customary axes available. Some machines will cut to a depth on the Y axis and index the rotary table automatically. The largest gears are produced on these machines.
Other operations such as broaching work particularly well for cutting teeth on the inside. The downside to this is that it is expensive and different broaches are required to make different sized gears. Therefore it is mostly used in very high production runs.
on a milling machine
or jig grinder
utilizing a numbered gear cutter, and any indexing head
or rotary table. The number of the gear cutter is determined by the tooth count of the gear to be cut.
To machine a helical gear on a manual machine, a true indexing fixture must be used. Indexing fixtures can disengage the drive worm, and be attached via an external gear train
to the machine table's handle (like a power feed). It then operates similarly to a carriage on a lathe. As the table moves on the X axis, the fixture will rotate in a fixed ratio with the table. The indexing fixture itself receives its name from the original purpose of the tool: moving the table in precise, fixed increments. If the indexing worm is not disengaged from the table, one can move the table in a highly controlled fashion via the indexing plate to produce linear movement of great precision (such as a vernier scale).
There are a few different types of cutters used when creating gears. One is a rack shaper. These are straight and move in a direction tangent to the gear, while the gear is fixed. They have six to twelve teeth and eventually have to be moved back to the starting point to begin another cut.
A popular way to build gears is by form cutting. This is done by taking a blank gear and rotating a cutter, with the desired tooth pattern, around its periphery. This ensures that the gear will fit when the operation is finished.
and using a tool shaped in the profile of the tooth to be cut. This method also works for cutting internal splines.
Another is a pinion-shaped cutter that is used in a gear shaper machine. It is basically when a cutter that looks similar to a gear cuts a gear blank. The cutter and the blank must have a rotating axis parallel to each other. This process works well for low and high production runs.
, burnishing, grinding, honing
or lapping
.
Gear
A gear is a rotating machine part having cut teeth, or cogs, which mesh with another toothed part in order to transmit torque. Two or more gears working in tandem are called a transmission and can produce a mechanical advantage through a gear ratio and thus may be considered a simple machine....
. The most common processes include hobbing, broaching, and machining; other processes include shaping
Shaping
Shaping can refer to:* In electricity generation, maintaining reliable delivery, for example by use of pumped storage hydroelectricity* Shaping , the reinforcement of successive approximations to train a type of behavior...
, forging
Forging
Forging is a manufacturing process involving the shaping of metal using localized compressive forces. Forging is often classified according to the temperature at which it is performed: '"cold," "warm," or "hot" forging. Forged parts can range in weight from less than a kilogram to 580 metric tons...
, extruding
Extrusion
Extrusion is a process used to create objects of a fixed cross-sectional profile. A material is pushed or drawn through a die of the desired cross-section...
, casting
Casting
In metalworking, casting involves pouring liquid metal into a mold, which contains a hollow cavity of the desired shape, and then allowing it to cool and solidify. The solidified part is also known as a casting, which is ejected or broken out of the mold to complete the process...
, and powder metallurgy
Powder metallurgy
Powder metallurgy is the process of blending fine powdered materials, pressing them into a desired shape , and then heating the compressed material in a controlled atmosphere to bond the material . The powder metallurgy process generally consists of four basic steps: powder manufacture, powder...
. Gears are commonly made from metal
Metal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...
, plastic
Plastic
A plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...
, and wood
Wood
Wood is a hard, fibrous tissue found in many trees. It has been used for hundreds of thousands of years for both fuel and as a construction material. It is an organic material, a natural composite of cellulose fibers embedded in a matrix of lignin which resists compression...
.
Broaching
For very large gears or splineRotating spline
Splines are ridges or teethon a drive shaft that mesh with grooves in a mating piece and transfer torque to it, maintaining the angular correspondence between them....
s, a vertical broach is used. It consists of a vertical rail that carries a single tooth cutter formed to create the tooth shape. A rotary table
Rotary table
A rotary table is a precision work positioning device used in metalworking. It enables the operator to drill or cut work at exact intervals around a fixed axis...
and a Y axis are the customary axes available. Some machines will cut to a depth on the Y axis and index the rotary table automatically. The largest gears are produced on these machines.
Other operations such as broaching work particularly well for cutting teeth on the inside. The downside to this is that it is expensive and different broaches are required to make different sized gears. Therefore it is mostly used in very high production runs.
Hobbing
Hobbing is a method by which a hob is used to cut teeth into a blank. The cutter and gear blank are rotated at the same time to transfer the profile of the hob onto the gear blank. The hob must make one revolution to create each tooth of the gear. Used very often for all sizes of production runs, but works best for medium to high.Machining
Spur may be cut or groundGrinding (abrasive cutting)
Grinding is an abrasive machining process that uses a grinding wheel as the cutting tool.A wide variety of machines are used for grinding:* Hand-cranked knife-sharpening stones * Handheld power tools such as angle grinders and die grinders...
on a milling machine
Milling machine
A milling machine is a machine tool used to machine solid materials. Milling machines are often classed in two basic forms, horizontal and vertical, which refers to the orientation of the main spindle. Both types range in size from small, bench-mounted devices to room-sized machines...
or jig grinder
Jig grinder
A jig grinder is a machine tool used for grinding complex shapes and holes where the highest degrees of accuracy and finish are required.The jig grinder is very similar to a jig borer, in that the table positioning and spindles are very accurate...
utilizing a numbered gear cutter, and any indexing head
Indexing head
An indexing head, also known as a dividing head or spiral head, is a specialized tool that allows a workpiece to be circularly indexed; that is, easily and precisely rotated to preset angles or circular divisions...
or rotary table. The number of the gear cutter is determined by the tooth count of the gear to be cut.
To machine a helical gear on a manual machine, a true indexing fixture must be used. Indexing fixtures can disengage the drive worm, and be attached via an external gear train
Gear train
A gear train is formed by mounting gears on a frame so that the teeth of the gears engage. Gear teeth are designed to ensure the pitch circles of engaging gears roll on each other without slipping, this provides a smooth transmission of rotation from one gear to the next.The transmission of...
to the machine table's handle (like a power feed). It then operates similarly to a carriage on a lathe. As the table moves on the X axis, the fixture will rotate in a fixed ratio with the table. The indexing fixture itself receives its name from the original purpose of the tool: moving the table in precise, fixed increments. If the indexing worm is not disengaged from the table, one can move the table in a highly controlled fashion via the indexing plate to produce linear movement of great precision (such as a vernier scale).
There are a few different types of cutters used when creating gears. One is a rack shaper. These are straight and move in a direction tangent to the gear, while the gear is fixed. They have six to twelve teeth and eventually have to be moved back to the starting point to begin another cut.
A popular way to build gears is by form cutting. This is done by taking a blank gear and rotating a cutter, with the desired tooth pattern, around its periphery. This ensures that the gear will fit when the operation is finished.
Shaping
The old method of gear cutting is mounting a gear blank in a shaperShaper
A shaper is a type of machine tool that uses linear relative motion between the workpiece and a single-point cutting tool to machine a linear toolpath. Its cut is analogous to that of a lathe, except that it is linear instead of helical...
and using a tool shaped in the profile of the tooth to be cut. This method also works for cutting internal splines.
Another is a pinion-shaped cutter that is used in a gear shaper machine. It is basically when a cutter that looks similar to a gear cuts a gear blank. The cutter and the blank must have a rotating axis parallel to each other. This process works well for low and high production runs.
Finishing
After being cut the gear can be finished by shavingShaving
Shaving is the removal of hair, by using a razor or any other kind of bladed implement, to slice it down to the level of the skin. Shaving is most commonly practiced by men to remove their facial hair and by women to remove their leg and underarm hair...
, burnishing, grinding, honing
Honing
Honing may refer to:* Honing , machining a surface by scrubbing an abrasive stone against it* Sharpening edged tools with a manual hone* Henkjan Honing , Dutch musician* Honing, Norfolk, English village* Playing Heroes of Newerth...
or lapping
Lapping
Lapping is a machining operation, in which two surfaces are rubbed together with an abrasive between them, by hand movement or by way of a machine.This can take two forms...
.