Not to be confused with Hobbling.
A hob — the cutter used for hobbing.
Hobbing is Jasa Hobbing 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, cylindrical piece of metal) by a series of cuts made by a cutting tool called a hob. Compared to other gear forming processes it is relatively inexpensive but still quite accurate, thus it is used for a broad range of parts and quantities.
It is the most widely used gear cutting process for creating spur and helical gears[dua] and more gears are cut by hobbing than any other process as it is relatively quick and inexpensive.[tiga]
A type of skiving that is analogous to the hobbing of external gears can be applied to the cutting of internal gears, which are skived with a rotary cutter (rather than shaped or broached).Process
Spur gears on horizontal CNC gear hobbing machine
Spur gears on horizontal CNC gear hobbing machine
Hobbing uses a hobbing machine with two skew spindles, one mounted with a blank workpiece and the other with the hob. The angle between the hob’s spindle (axis) and the workpiece’s spindle varies, depending on the type of product being produced. For example, if a spur gear is being produced, then the hob is angled equal to the lead angle of the hob; if a helical gear is being produced then the angle must be increased by the same amount as the helix angle of the helical gear. The hobbing features for gears are straight, helical, straight bevel, face, crowned, worm, cylkro and chamfering.  The two shafts are rotated at a proportional ratio, which determines the number of teeth on the blank; for example, for a single-threaded hob if the gear ratio is 40:1 the hob rotates 40 times to each turn of the blank, which produces 40 teeth in the blank. If the hob has multiple threads the speed ratio must be multiplied by the number of threads on the hob. The hob is then fed up into the workpiece until the correct tooth depth is obtained. Finally the hob is fed through the workpiece parallel to the blank’s axis of rotation.
Often, during mass production multiple blanks are stacked using a suitable fixture, then cut in one operation.
For very large gears the blank can be gashed to the rough shape first to make hobbing easier.Equipment
A horizontal CNC gear hobbing machine
Hobbing machines, also known as hobbers, are fully automated machines that come in many sizes, because they need to be able to produce anything from tiny instrument gears up to 10 ft (tiga.0 m) diameter marine gears. Each gear hobbing machine typically consists of a chuck and tailstock, to hold the workpiece or a spindle, a spindle on which the hob is mounted, and a drive motor.[tiga]
For a tooth profile which is a theoretical involute, the mendasar rack is straight-sided, with sides inclined at the pressure angle of the tooth form, with flat top and bottom. The necessary addendum correction to allow the use of small-numbered pinions can either be obtained by suitable modification of this rack to a cycloidal form at the tips, or by hobbing at other than the theoretical pitch circle diameter.Since the gear ratio between hob and blank is fixed, the resulting gear will have the correct pitch on the pitch circle, but the tooth thickness will not be equal to the space width.
Hobbing machines are characterised by the largest module or pitch diameter it can generate. For example, a 10 in Jasa Hobbing (250 mm) capacity machine can generate gears with a 10 in pitch diameter and usually a maximum of a 10 in face width. Most hobbing machines are vertical hobbers, which means the blank is mounted vertically. Horizontal hobbing machines are usually used for cutting longer workpieces; i.e. cutting splines on the end of a shaft.Hob
A gear hob in a hobbing machine with a finished gear.
The hob is a cutting tool used to cut the teeth into the workpiece. It is cylindrical in shape with helical cutting teeth. These teeth have grooves that run the length of the hob, which aid in cutting and chip removal. There are also special Jasa Hobbing hobs designed for special gears such as the spline and sprocket gears.
The cross-sectional shape of the hob teeth are almost the same shape as teeth of a rack gear that would be used with the finished product. There are slight changes to the shape for generating purposes, such as extending the hob’s tooth length to create a clearance in the gear’s roots. Each hob tooth is relieved on the back side to reduce friction.
Most hobs are single-thread hobs, but double-, and triple-thread hobs increase production rates. The downside is that they are not as accurate as single-thread hobs.Depending on type of gear teeth to be cut, there are custom made hobs and general purpose hobs. Custom made hobs are different from other hobs as they are suited to make gears with modified tooth profiles. The tooth profile is modified to add strength and reduce size and gear noise.
This list outlines types of hobs:Roller chain sprocket hobsWorm wheel hobsSpline hobsChamfer hobsSpur and helical gear hobsStraight side spline hobsInvolute spline hobsSerration hobsSemitopping gear hobs
Hobbing is used to make the following types of finished gears:Cycloid gears (see below)Helical gearsInvolute gearsRatchetsSplinesSprocketsSpur gearsWorm gears
Hobbing is used to produce most throated worm wheels, but certain tooth profiles cannot be hobbed. If any portion of the hob profile is perpendicular to the axis then it will have no cutting clearance generated by the usual backing off process, and it will not cut well.Cycloidal forms
For cycloidal gears (as used in BS978-dua Specification for fine pitch gears) and cycloidal-type gears each module, ratio and number of teeth in the pinion requires a different hobbing cutter, so the technique is only suitable for large volume production.
To circumvent this problem a special war-time emergency circular arc gear standard was produced giving a series of close-to-cycloidal forms which could be cut with a single hob for each module for eight teeth and upwards to economize on cutter manufacturing resources.A variant on this is still included in BS978-2a (Gears for instruments and clockwork mechanisms. Cycloidal type gears. Double circular arc type gears).
Tolerances of concentricity of the hob limit the lower modules which can be cut practically by hobbing to about 0.lima module.History
Christian Schiele of Lancaster England, patented the hobbing machine in 1856.[self-published source] It was a simple machine, but the rudimentary parts are present in the customary patent drawings.The hob cutting tool and the gear train to provide the appropriate ratio are clearly visible.Knowledge of hobbing probably precedes his patent likely within the watchmaking trades.