Gear Manufacturing

Table of Contents

Gear Manufacturing Resources and Companies

Depending on the application requirements, it may be sufficient to use traditional methods like hobbing or shaping to cut the gear teeth. These methods use a high speed steel or carbide cutting tool with a specific form to remove material from a circular gear blank. These tools produce good dimensional accuracy and good surface finishes appropriate for a wide range of applications. If more precision is required, or if the gears are required to run quietly, shaving or grinding may be required to produce a finer surface finish and more precise tooth locations and forms.

Manufacturing Metal Gears

Gear Prototyping Methods

To manufacture just a few gears, a process that doesn't use specialized cutters or machines is a good choice. A wire EDM machine, which uses a very fine electrically charged wire to erode material, can be used to cut any gear with a straight tooth profile very accurately. Wire EDM machines are also very useful for other prototyping tasks and not only for gears. This article from Gear Technology describes how the machine works, what sort of tolerances are possible, and describes one company's method of making precise master gears with wire EDM. 

A Sinker EDM can also be used to make gears with helical teeth, but this requires one or more custom electrodes.

Gear Manufacturing Using a Manual Milling Machine

The following article details how to machine a simple spur gear on a milling machine using a dividing head. A specifically shaped cutter must be used. 

Making spur gears using a dividing head - This resource covers how to select a cutter, prepare the gear blank, and set up a dividing head on a horizontal or vertical milling machine. Is is critical that great care is taken at every step of the process to ensure the best results. 

Gear Manufacturing in a Production Environment

Companies that specialize in gear production use processes like hobbing, shaping,  skiving, and grinding. 

Manufacturing Plastic Gears

Although plastic gears can also be cut using many of the same methods as metal gears, injection molding or extrusion is better suited to the mass production of gears from plastics. 

As described in the page gear selection, plastic gears are often an excellent choice where many low cost, lightly loaded, gears are needed. Designing an mold for such a gear is quite a difficult process- as the part is cooled, it will shrink and change shape, especially if there are sharp corners, big changes in the cross section of the gear, or thick sections. This article from Stock Drive Products / Sterling Instruments explains many of these considerations. One big advantage is that many of the form and size issues with molded plastic gears are well tolerated by the softer material and the gears can often be used with minimal or no lubrication.

Gear Inspection

If large amounts of gears are required or the application has strict quality and durability requirements, inspection is likely needed to ensure that the gears meet the design requirements. One of the simplest tests is to mesh the gear with a master gear and measure the variation in centre distance as the gear meshes with the master. If there is no error in either gear, the centre distance will remain constant. This is an excellent functional test because centre distance variation will contribute to inconsistent motion, cause excess noise, and can make the gears difficult to install in the gearbox.

Measuring the variation in centre distance is a great way to assess the quality of a gear, but might not explain what is causing the defects. Using a thin bluing agent spread on one of the gears, such as Prussian Blue, can highlight exactly where the gears are contacting. If the contact is not happening in the centre of the flank, the tooth profile is likely distorted.

References

[1] Penta Gear Metrology, "Double Flank Inspection Manual Hand Roller," Direct Industry, 2020. [Online]. Available: https://pdf.directindustry.com/pdf/peco/double-flank-inspection-manual-hand-roller/53637-631450.html. [Accessed: November 10, 2020].

[2] John F's Workshop, "Making Spur Gears Using a Dividing Head," John F's Workshop, 2015. [Online]. Available: https://johnfsworkshop.org/home/making-other/gears-links/making-spur-gears-links/dividing-head-making-spur-gears/.  [Accessed: November 10, 2020].