Gear cutting is the process of creating a gear. Sobbing, broaching, milling and grinding are
the main gear-cutting processes. Gear cutting tools play a very important role in creating a
gear. They are the main tools used to create a gear.
Given below are tips to choose gear cutting tools-
. 1. The hob is a cutting tool used to cut the teeth in the workpiece in hobbing process. Its
shape is cylindrical and it has helical cutting teeth. These teeth have got grooves that run the
length of the hob, which help in cutting and chip removal. For special gears like spline and
sprocket, special hobs are designed.
The cross-sectional shape of the hob teeth are of the same shape as teeth of a rach gear used
with the finished product. The hob’s tooth is extended to create a clearance in the gear’s
roots. Majority of hobs are single thread, but double and triple threads increase production
rates. But they aren’t as accurate as single-thread hobs.
There are custom made hobs to make gears with modified tooth profiles. There are roller
chain sprocket hobs, chamfer hobs, spur and helical gear hobs, straight side spline hobs,
involute spline hobs, serration hobs and smith topping gear hobs. For certain tooth profiles
hobbing can’t be used. If any portion of the hob profile is perpendicular to the axis then it
will have no cutting clearance and won’t cut well.
- With milling, the gear wheel is held steady while a milling cutter advances axially along
the face width of the gear blank. This process is used to rough or semi finish the tooth space
with extra stack allowance for hobbing, grinding, shaving or it can complete the tooth space
to finish the form. Gear milling cutters can be mounted to produce two or more spaces, and
they can be constructed of steel bodies with removable carbide inserts.
In some cases, they are made to accept re-grindable carbide blades, but with modern
precision grinding techniques for carbide inserts, such tools are redundant. Solid carbide tools
are used occasionally but due to the high cost and size limitations of solid carbide, they are
becoming less popular. Though high-speed steel cutters can be made at low cost, they offer
limited speed capability and are used for low volume gears and smaller module sizes, as the
high cost of high-speed steel material make larger size cutters impractical. Gear milling
cutters with tangentially mounted inserts are commonplace.
They are economical, as they have carbide inserts with multiple edges. Newer designs have
inserts with positive cutting geometry, but it is limited to roughing, and semi finishing tools
that don’t require precise, full profile inserts. Such inserts are ground for gear manufacturer’s
requirements, hence costly insert pressing tools aren’t made unless there is a very high value
to justify it.
- Grinding wheel is used as a cutting tool in grinding process. It is composed of an abrasive
compound and made from a composite material.
- A toothed tool known as a broach is used in the machining process broaching. They are
shaped similar to a saw and height of the teeth increases over the length of the tool. The
broach has three sections- one for roughing, another for semi finishing, and the third one for
Hob, gear milling cutters, grinding wheel and broach are the tools used for gear cutting and
these tools should be chosen after a proper research and careful consideration.