Gashing is a

machining Machining is a process in which a material (often metal) is cut to a desired final shape and size by a controlled material-removal process. The processes that have this common theme are collectively called subtractive manufacturing, which utilizes ...

process used to rough out coarse pitched

gear A gear is a rotating circular machine part having cut teeth or, in the case of a cogwheel or gearwheel, inserted teeth (called ''cogs''), which mesh with another (compatible) toothed part to transmit (convert) torque and speed. The basic pr ...

s and

sprocket A sprocket, sprocket-wheel or chainwheel is a profiled wheel with teeth that mesh with a chain, track or other perforated or indented material. The name 'sprocket' applies generally to any wheel upon which radial projections engage a chain passi ...

s. It is commonly used on

worm wheel A worm drive is a gear arrangement in which a worm (which is a gear in the form of a screw) meshes with a worm wheel (which is similar in appearance to a spur gear). The two elements are also called the worm screw and worm gear. The terminolo ...

s before

hobbing Hobbing is a machining process for gear cutting, cutting splines, and cutting sprockets on a hobbing machine, which is a special type of milling machine. The teeth or splines of the gear are progressively cut into the material (a flat, cylind ...

, but also used on

internal Internal may refer to: *Internality as a concept in behavioural economics *Neijia, internal styles of Chinese martial arts *Neigong or "internal skills", a type of exercise in meditation associated with Daoism *''Internal (album)'' by Safia, 2016 ...

and

external External may refer to: * External (mathematics), a concept in abstract algebra * Externality In economics, an externality or external cost is an indirect cost or benefit to an uninvolved third party that arises as an effect of another party' ...

spur gear Spur gears or straight-cut gears are the simplest type of gear. They consist of a cylinder or disk with teeth projecting radially. Viewing the gear at 90 degrees from the shaft length (side on) the tooth faces are straight and aligned parallel to ...

bevel gear Bevel gears are gears where the axes of the two shafts intersect and the tooth-bearing faces of the gears themselves are conically shaped. Bevel gears are most often mounted on shafts that are 90 degrees apart, but can be designed to work at oth ...

helical gear A gear is a rotating circular machine part having cut teeth or, in the case of a cogwheel or gearwheel, inserted teeth (called ''cogs''), which mesh with another (compatible) toothed part to transmit (convert) torque and speed. The basic p ...

s, and

gear rack A rack and pinion is a type of linear actuator that comprises a circular gear (the ''pinion'') engaging a linear gear (the ''rack''). Together, they convert rotational motion into linear motion. Rotating the pinion causes the rack to be driven i ...

s. The process is performed on ''gashers'' or universal milling machines, especially in the case of worm wheels. After gashing the gear or sprocket is finished via hobbing, shaping, or

shaving 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 or otherwise. Shaving is most commonly practiced by men to remove their facial hair and by women to remove the ...

Equipment

''Gashers'' are large, heavy-duty machine tools. They have horizontal and vertical slideways, precise indexing, large diameter

ballscrew A ball screw (or ballscrew) is a mechanical linear actuator that translates rotational motion to linear motion with little friction. A threaded shaft provides a helical raceway for ball bearings which act as a precision screw. As well as bein ...

s, and spindle drive motors up to . They are usually controlled via

computer numerical control Numerical control (also computer numerical control, and commonly called CNC) is the automated control of machining tools (such as drills, lathes, mills, grinders, routers and 3D printers) by means of a computer. A CNC machine processes a pie ...

(CNC) or a

microprocessor A microprocessor is a computer processor where the data processing logic and control is included on a single integrated circuit, or a small number of integrated circuits. The microprocessor contains the arithmetic, logic, and control circu ...

. While they are usually used for rough cutting, they are also sometimes used for finishing. For example, gashers are used for the production of large roller-chain sprockets.

Process

Gashing was first used to rough out worm wheels using a universal milling machine, but then dedicated gashers were built to rough out other types of gears. Because the processes is carried out on two different machines the process differs.

Universal milling machine

The process uses a

milling cutter Milling cutters are cutting tools typically used in milling machines or machining centres to perform milling operations (and occasionally in other machine tools). They remove material by their movement within the machine (e.g., a ball nose mill) ...

with a cross-section that is slightly smaller than the final cross-section of the cut; it has the same diameter as the

worm Worms are many different distantly related bilateral animals that typically have a long cylindrical tube-like body, no limbs, and no eyes (though not always). Worms vary in size from microscopic to over in length for marine polychaete wor ...

. The cutter is then angled to the ''gashing angle''. The gashing angle is calculated from the

lead Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...

and pitch diameter of the worm; often tables are available with the gashing angles for common diameters and leads. The cutter is centered over the blank and then plunged into it to the proper depth. The cutter is finally withdrawn and the blank indexed to the next tooth space and cut. This is repeated until all of the tooth spaces have been cut.. Note that a standard

endmill An end mill is a type of milling cutter, a cutting tool used in industrial milling applications. It is distinguished from the drill bit in its application, geometry, and manufacture. While a drill bit can only cut in the axial direction, most m ...

with rounded corners can be used instead if a special milling cutter is unavailable. The endmill should be the pitch diameter.. Note that is process cannot be used on a small worm wheel that mate with a multiple threaded worm.

Gasher

The process is similar to that outlined for the universal milling machine except a gashing angle is not used. When gashing spur gears, racks, or bevel gears the cutter is plunged into the workpiece and then moved linearly in the proper direction. If a helical gear is being roughed out, then the table rotates and moves along the vertical axis to

interpolate In the mathematical field of numerical analysis, interpolation is a type of estimation, a method of constructing (finding) new data points based on the range of a discrete set of known data points. In engineering and science, one often has a n ...

the helical path. The two most common cutting tools are formed milling cutters and cutters with indexable carbide inserts. For very large gears a cutter might be replaced with two slitting cutters that cut triangular slugs from the blank.

References

Bibliography

*. *. *{{Citation , last = Oberg , first = Erik , title = Spiral and worm gearing , publisher = The Industrial Press , year = 1917 , url = https://books.google.com/books?id=wUJVAAAAMAAJ , pages = 296 .

External links

Table of gashing angles
Gears Machining