Quality 101: Measuring Gear Shafts
Several types of measurements generally are required in the manufacturing process for gear shafts. Gages may be used for interoperational measurements to control quality at different stages within the manufacturing process, or for final inspection at the end of production. Normally it is desirable to check both the dimensional as well as the functional parameters of gear shaft parts. While it is possible to combine dimensional measurements and functional checks on gear teeth in a single gaging device, these inspections sometimes are conducted using separate gages as the manufacturing operations for the shafts and gears are performed in separate stages at the shop.
The most efficient means of checking dimensional and geometric measurements on the cylindrical shaft portion of gear shafts in a production environment involves multidimensional contact-type gages. Today's modular, retoolable manual bench gages may be configured using various types of part measuring assemblies that can accommodate either pencil probes or dial or digital indicators for measuring diameters, shoulders and lengths. Measurement readings may be displayed on direct-reading dial or digital indicators, or by interfacing the probes with an electronic display unit. Different part support options permit static or dynamic measurements. Alternatively, a noncontact optical measuring system can be applied for a higher level of flexibility.
Gear dimensional inspection
Dimensional inspection of shaft gears normally is
performed after hobbing, grinding or honing of the gear teeth. These checks can be accomplished using an over ball dimension (OBD) measurement system for diameter verification using calibrated spheres, or balls, or rollers, or pins. In a typical retoolable OBD manual bench system, the part is held between centers, and different longitudinal sections can be separately or simultaneously checked. Additionally, minor, or root, and major diameter measurements can be performed using a special multiple-contact turret on the gage.
An over ball radius gage, which also uses calibrated balls or pins, can be used for radius verification on even or odd teeth on gear shafts. A turret on the gage can accommodate up to seven different contact arrangements for measuring parameters such as pitch, root or major radius.
Measuring the dimensional relationship between the cylindrical shaft and gear is necessary for controlling quality of gear shafts. For example, after rough machining and before heat treatment and finishing a gear shaft, the manufacturer can use an interoperational gage to verify concentricity between the gear pitch diameter and bearing diameters on the shaft. Checking the part at this stage avoids producing scrap parts and wasting valuable processing in the case of an out-of-
Gear shafts can be tested functionally by measuring the total effect of gear errors against a master gear. These tests simulate operating conditions resulting from gears meshing together. The master gear tolerances define the maximum variation for total composite errors and tooth-to-tooth errors. When the master gear and part are tightly meshed and running together, composite variation is viewed by monitoring the position of the master gear with a comparative indicator.
The most common method of functional testing is double-flank inspection, which checks five parameters: tooth-to-tooth radial deviation, total radial deviation, part runout, nicks
and center-distance variation. During double-flank inspection, the teeth of the gear component and the master gear are conjugate one to the other, without clearance. So, one tooth meshes with the other and touches both flanks of each individual tooth.
The part being inspected is mounted on a precision fixed arbor. A precision master gear is mounted to an adjustable slide and moved forward until its tooth tightly meshes with the part, producing contact on both flanks of the root diameter of the part. The part is inspected as conjugate against the master gear to verify the center distance variation. The tooth-to-tooth variation and total composite variation between the part and the master gear are determined when rolling them together changes their center distance. Linear variable differential transformer measuring cells are used to measure variations.
Gear shaft manufacturers also may conduct single-flank inspection when they wish to duplicate the performance of the gear in its intended application.
In a transmission, for example, there is clearance, or backlash, when one gear meshes with another gear, and the gear works in both directions. Single-flank inspection replicates this condition by mounting the master gear and the part at a fixed operating distance matching the clearance of the assembled gears. It produces contact on a single flank of each meshing tooth. The measuring principle is based on an accurate reading of two rotary encoders attached to the input and output shafts holding the master gear and the gear to be checked. Rotating clockwise touches one side of the tooth. Counterclockwise rotation touches the other side. Single-flank inspection checks the tangential deviation, the tangential total deviation and the sectorial tangential deviation.
Gear shaft manufacturers also might inspect parts for noise that can be created by nicks caused by mishandling a green part before heat treating. Noise also can be created by burrs located where the involute profile meets the gear face, or if scale is left on the gear after heat treating. Noise analysis systems incorporated into gages use accelerometer sensors. This capability identifies acoustic defects, weak points and faults because of out-out-tolerance assembly, mounting mistakes or functional defects, manufacturing errors and damages. Based on evaluations of recorded noise patterns, gears under test are categorized as good, reject or rework.
Manual or semi-automatic bench gages typically are used by shops inspecting 25,000 to 100,000 parts annually. But in high-volume operations, checking 800,000 to 2 million gear shafts a year, fully automated systems using sophisticated software analysis are recommended.
Newer systems now offer all-in-one gaging-gear inspection, double-flank testing, single-flank testing, as well as noise vibration analysis-in a single unit using one electronic system.
By fitting each type of transducer required for these respective checks into one electronic framework, new gaging systems separate and analyze problems working together in different environments. As a result, an operator can simultaneously perform double-flank and single-flank measurements, or check the single flank with noise analysis.
Gary Sicheneder is manager of market development at Marposs Corp. (Auburn Hills, MI). For more information, call (888) 627-7677 or visit www.us.marposs.com.