A new fixture design minimizes runout and helps ensure greater accuracy for hard finishing and inspection.

Gear manufacturers are turning to workholding to help reduce costs without compromising quality. Pitch Line Fixtures, for example, can be used to provide a more precise relationship between the pinion/gear member datums and the gear teeth, thus reducing the amount of runout on those datums relative to the pitch diameter (pitch line) of the gear or pinion. Since undesirable runout results from heat treatment and other manufacturing processes that can cause distortion, Pitch Line Fixtures are particularly well suited for hard finishing and inspection applications.

Gleason has developed a Pitch Line Fixture that will average gear member runout to within 0.0005” (0.0127 mm) to the pitch line — and can be as accurate as 0.0002” (0.005 mm). (Courtesy: Gleason)

A Better Mousetrap

Gleason has developed a Pitch Line Fixture that will average gear member runout to within 0.0005” (0.0127 mm) to the pitch line — and can be as accurate as 0.0002” (0.005 mm). The application determines the required accuracy. If used in a grinding application where normally 0.004” (0.1016 mm) of stock is removed off each gear flank, then the runout to the bearing journals of 0.0005” (0.0127 mm) would be sufficient. However, if used for hard turning with no subsequent finishing or lapping applications, then 0.0002” (0.005 mm) would be more appropriate.

Gleason Pitch Line Fixtures are designed with the pitch pins perpendicular to the gear tooth pitch diameter for optimized strength, accuracy, and wear. This offers significant advantages over conventional designs, where the pins in a pitch line fixture point straight up (parallel to the axis of the part) resulting in a reduction in radial accuracy and stiffness of the centering function. For example, in pinions with a slim pitch angle of 20°, the forces on the balls and the pins are not directedin the axial pin direction, thereby reducing the force perpendicular to the pitch angle to only 34 percent (sin20°) in the axial pin direction and 94 percent (cos20°) perpendicular to the pin. This high perpendicular force will ultimately wear the pin sleeves and also bend the pins. In the case of ring gears, this effect is smaller, but the same accuracy and wear issues will occur over time.

Figure 1: Pitch Line Fixture with spring-loaded center in which the part can be positioned off the center and then lowered onto the pins for hard turning, grinding, or inspection.
Figure 2: Pitch Line Fixture equipped with hydraulic quick-change base equipment, for applications where the customer requires fast changeover of multiple part types.

Application Versatility

Pitch Line Fixtures can be designed to meet the needs of a wide range of customer workholding applications: mechanically or hydraulically actuated, tailstock driven, compatible with quick change base equipment, incorporating a spring-loaded pre-centering mechanism, and including mechanically activated holding jaws.

The recommended clamping method is determined by the application. For example, a pinion being held in the Pitch Line Fixture by a tailstock would not require clamp blocks on the pinion head for holding the pinion in place.

For a ring gear member, straps are often used on the back angle if the process requires that the bore be machined as well as the mounting surface. These pitch line features would be incorporated as required into the design of the fixture. 

Each module consists of an interchangeable clamping head connected to an interchangeable arbor body. (Courtesy: Gleason)

SIDEBAR: Workholding solutions

Modular Standard Workholding: For greater speed and flexibility

Another significant workholding breakthrough is Gleason’s new Modular Standard Workholding, which puts the performance benefits of tool-less quick change workholding into a system of standard, interchangeable, and readily available modules.

In recent years, Gleason’s Quik-Flex® and Quik-Flex®Plus systems have revolutionized workholding changeover for small- and medium-size cylindrical gears with a system of modules that can be installed on a base arbor permanently mounted in the work spindle with just the twist of an activation handle.

These new solutions can be installed and removed in just seconds, with only a single tool, and by even a novice.

With introduction of a system of Modular Standard Workholding, Gleason puts this same Quik-Flex performance into a system of small, medium and large standard interchangeable modules that span the most common range of gear diameters.

Now, there’s an in-stock, off-the-shelf solution available to users almost overnight to meet the latest workholding requirements of many of the most common cylindrical gear bore sizes and diameters.

End result: elimination of many weeks of waiting, and the inherent cost, for special tooling whenever a new application arises.

Each module consists of an interchangeable clamping head connected to an interchangeable arbor body, both of which come in a variety of sizes to form a multitude of standard combinations to fit the user’s part specific application requirements.

These modules interface with just three sizes of Quik-Flex base adapter, permanently mounted in the work spindle.

The base unit is designed to be fine-tuned during its installation for minimal axial and radial runout. Most importantly, the modules can be installed, and removed, in just seconds with just a quick twist of the system’s simple, removable, activation handle.

No other tools are required, nor are there any of the usual mounting bolts, set screws, or ejector screws to deal with.

Note that an internal cam locking mechanism built into the base ensures that modular colleting tooling is centered and drawn firmly against the seating face of the base.

Most importantly, Modular Standard Workholding makes no compromises on quality. Accuracies and repeatability of 5 microns (0.0002”) TIR — identical to other Gleason workholding — are guaranteed.

For more information on how Gleason Pitch Line Fixtures can be used to help reduce cost and improve accuracy, go to www.gleason.com.