Gear cutters and hobs are tools for machining gear-tooth profiles. They are ground to produce teeth, usually of an involute form, in standard American pitches or metric modules. Specialty or custom gear hobs are frequently available from gear hob suppliers.
Gear cutters and hobs may be of solid construction, or with holders and inserts. They can be used with a number of end or tip geometry options, including square end, ball nose, radius tip, and chamfer tip. Square end tip geometry for gear cutters and hobs have a square or straight end that features no radius, chamfer, or other finish. Ball nose gear cutters and hobs tips have a “ball nose” whose radius is one half of the cutter diameter. This type of gear cutters and hobs tip is useful for machining female semicircle grooves of radii.
Other ends and tips for gear cutters and hobs include radius or chamfer-tipped. Radius-tipped gear cutters and hobs ends are straight flutes with ground radius on the very tip. Chamfer tip ends feature an angled section of the side or the end. These tips produce an angled cut of chamfered edge on a workpiece.
When selecting a gear cutters and hobs, consideration must be made to the desired finish type. There are typically two finish options: roughing / hogging and finishing. Roughing and hogging mills are designed so that the machine geometry, flutes, and materials can be used for rapid and heavy material removal. They are typically used to machine workpieces close to the desired finishing dimensions, where a finishing gear cutters and hobs takes over and produces closer tolerances and higher-quality surface finish.
Other considerations for gear cutters and hobs include cutter size and construction criteria. Size considerations for gear cutters and hobs relate to the cutting diameter, shank or arbor diameter, flute or cutting edge length, overall tool length, and radius dimension and angle when applicable. Construction options for gear cutters and hobs include the number of flutes of cutting edges. This number can vary with the cutter diameter, milling material, and other factors. Two-flute gear cutters and hobs are often used with ductile materials that produce long chips. Gear cutters and hobs using higher-number of flutes can be used to minimize chip load and vibration.
The material of the gear cutters and hobs is important for understanding the level of cutting the machine can handle. Materials like carbide, cobalt, and diamond are hard and can be used in high-speed applications, whereas materials like steel are used for general metal machining. Other material options for gear cutters and hobs include micrograin carbide, which is used most-often in surface finishing applications, and ceramic.
Coatings for gear cutters and hobs are important considerations as well, as they can provide additional production against corrosion and abrasion, increase the tool’s hardness, provide lubrication and smoothness assistance, and improve the overall lifetime of the tool. Other considerations and options for gear cutters and hobs may also be required depending on the manufacturer.