32 GEAR SOLUTIONS • JUNE 2005 • gearsolutionsonline.
com
IN ADDITION TO CHECKING PART SIZE AND
QUALITY, GEAR INSPECTION PROVIDES INSIGHTS
INTO THE MANUFACTURING PROCESS ITSELF,
INSURING THAT YOUR OWN PROCEDURES ARE
PROPERLY CONTROLLED.
By Dennis Gimpert
ear inspection begins with the everyday tasks on the shop floor and
G
FIGURE 1 — Measurement of size with micrometer and
extends into the manufacturing laboratory for complex analytical gear pins or balls.
evaluation. Some, or all, of these procedures are necessary to main-
tain process control and to produce parts to the required quality. In
particular, inspection can help control the following:
• Size of the gear
• Quality of the gear
• Fixture mounting on the machine
• Machine set-up
• Part blank quality
• Accuracy of the cutting tool
• Mounting of the cutting tool
• Correct sharpening of the cutting tool
• Heat treat process
• Condition of the production equipment
The following information summarizes the basic elements of gear inspec-
tion beginning with the most simple and leading to the more complex.
FIGURE 2 — Measurement of size with tooth caliper.
Size Inspection
The traditional method of inspecting a gear for correct size is the measure-
ment over pins or balls with a micrometer. Pin measurement provides an
accurate and convenient method of determining tooth thickness of a gear
of any diameter within the capacity of the available micrometers. For larger
diameter gears a span measurement or gear tooth calipers can be used.
Composite testing can also provide a measurement of gear tooth size.
Size measurement is used to provide the correct backlash when the gear
is mounted with its mating gear at operating center distance.
Runout Inspection
Runout is the maximum variation of the distance between a surface of rev-
olution and a datum surface, measured perpendicular to that datum sur-
face. Runout of a gear can be measured with a dial indicator over a pin or
ball placed in successive tooth spaces. On modern CNC gear measuring
machines this inspection can be provided in a fully automatic cycle.
Runout measurement is used to assure correct backlash and minimum FIGURE 3 — Runout inspection with ball, pin, or anvil.
variation of rotary motion.
gearsolutionsonline.com • JUNE 2005 • GEAR SOLUTIONS 33
FIGURE 4 — Schematic concept of gear rolling device.
will allow variation in the center distance during rolling. This varia-
Composite Inspection tion in center distance will yield a “tooth-to-tooth” and a “total
The composite test of a gear is a method of inspection in which composite” indication that can be read on a simple dial indicator
the work gear is rolled in tight double flank contact with a master or recorded graphically.
gear. AGMA defines this type of inspection as “radial composite Composite inspection is a useful shop-friendly tool to determine
deviation.” No backlash is provided, as the work gear is spring- the general quality of a gear including size, runout, tooth-to-tooth
loaded against the reference gear on the inspection machine. The rolling action, and to detect nicks. It is not an appropriate method
composite action test is made on an inspection instrument that to determine individual tooth flank errors.
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34 GEAR SOLUTIONS • JUNE 2005 • gearsolutionsonline.com
FIGURE 5 — Graphical record from composite inspection.
measuring probe on the test gear in the middle of the gear face.
Most gear measuring machines use the generative principle to create
Profile Inspection a reference profile to compare to the gear’s actual profile. The profile
Profile is the shape of the gear tooth curve and is measured from the is traced and recorded graphically, with a correct unmodified profile
root to the tip of the gear tooth. The functional, or operating, portion being represented as a straight line on the chart.
of the profile is the area that is in actual contact during tooth mesh. Incorrect profile will cause a non-uniform rolling action of the
Typically, this area is from just above the root fillet to the tip of the gear, which may cause a large tooth-to-tooth error, uneven load-
tooth. On most parallel axis gears, the shape of the profile curve is ing, and noise problems. In extreme cases, premature gear fail-
an involute. In practice, an appropriate measuring machine aligns the ure may occur.
gearsolutionsonline.com • JUNE 2005 • GEAR SOLUTIONS 35
Total pitch variation and total index varia-
tion are identical values and are generally
referred to as “accumulated spacing.”
Total index variation is the maximum alge-
braic difference between the extreme val-
ues of index variation.
Two distinct methods are available to
arrive at tooth “spacing.” One utilizes a
single-probe measuring device with a pre-
cision indexing system. This indexing sys-
tem can be electronic, as on a CNC meas-
uring machine, with an encoder-controlled
rotary axis. It can also use mechanical
devices such as index plates, circular
divider, or optical scales. The second sys-
tem utilizes two probes to obtain succes-
sive data from adjacent tooth flanks as
the gear is rotated. The data obtained
from the two-probe system must be math-
FIGURE 6 — Profile inspection with degrees of roll, roll angle.
ematically corrected to obtain spacing val-
ues. It is recognized today that the single
probe system is the most accurate and
the preferred system.
“THE AGMA STANDARDS
REFERENCED IN THIS
PAPER ARE PRESENTLY
THE MOST ADVANCED
GEAR SPECIFICATIONS
FIGURE 7 — Graphic charting of helix deviation.
AVAILABLE IN THE WORLD.”
Helix Inspection
AGMA’s current inspection handbook defines “helix deviation” (formerly tooth alignment Index measurements are used to determine
variation and lead variation) as the difference between the measured helices to the design the correct spacing of gear teeth. Spacing
helices. In practice an appropriate measuring machine aligns the measuring probe on the error is the principle source of gear noise due
test gear at the pitch circle diameter and the “lead” is traced and recorded graphically, to total pitch variation or accumulated spacing.
with a correct unmodified helix being represented as a straight line on the chart. Helix Although the main component of total pitch
measurement is used to determine correct face contact between mating gears. Incorrect variation is from part runout, it may not be
helix will create uneven loading and noise. possible in all cases to detect this from a sim-
ple runout or composite inspection check.
Pitch or Index Inspection
Spacing is the theoretical true position of each tooth around the circumference of the gear. Single Flank Inspection
Pitch deviation is the difference between the theoretical position and the actual position of Single flank inspection appears to be iden-
each tooth. These values can be plus or minus. Index variation is the displacement of any tical with the composite, or double flank,
tooth from its theoretical position relative to a datum tooth. inspection technique. In fact, it is quite dif-
36 GEAR SOLUTIONS • JUNE 2005 • gearsolutionsonline.com
FIGURE 8 — Pitch measurement using a pitch comparator and angular indexing.
FIGURE 9 — Difference between double and single flank inspection.
ferent due to the fact that the test gear is rolled at its design cen- Single flank testing does not eliminate the need for analytical
ter distance and backlash with a master or reference gear. This inspection of helix deviation, and it is not as effectively applied to
closely simulates the operation of the actual gear. gear sets with increased contact ratios such as helical gears.
A single flank inspection instrument utilizes encoders on the two
axes of rotation either as a fixed or portable unit. The rotational
data from each encoder is then processed electronically, and the Summary
resulting phases are compared with each other to yield a phase The AGMA standards referenced in this paper are presently the
differential. This will indicate errors of rotational motion from the most advanced gear specifications available in the world. AGMA
ideal constant angular velocity of perfectly conjugate gears. The has worked with ANSI and with ISO to achieve this and presently
results of this phase difference are graphically recorded as an ana- chairs the ISO Gear Committee. The AGMA standard is a valuable
log waveform, similar to a composite inspection chart. specification not only to specify the level of gear accuracy but also
The most important aspect of single flank inspection is its ability to establish criteria between a vendor and a supplier, to measure
to measure profile conjugacy. The data is also related to profile accuracy capability of gear production equipment, or as a machine
variation, pitch variation, runout, and accumulated pitch variation. tool acceptance standard. Other specifications exist such as the
gearsolutionsonline.com • JUNE 2005 • GEAR SOLUTIONS 37
German Standard, DIN, the British Standard, BS, and the Japanese Standard, JIS.
Independent standards also exist based upon the experiences of individual manufacturers.
Wenzel GearTec, M & M Precision Systems, Klingelnberg, and other manufacturers offer
modern CNC controlled gear inspection machines to measure and record gear errors. Each
of these company’s machines are CNC controlled and, as such, offer additional capabilities
to measure other part parameters as well as the cutting and finishing tools that produce
the gear teeth. The CNC machines also offer the ability to link the measured data to a
computer system for automatic interpretation. A current development is to offer CMM type
inspection machines with gear inspection capability.
REFERENCES
Materials contained in this paper are
extracted from AGMA ISO 10064-2
“Cylindrical Gears—Code of Inspection
Related to Radial Composite Deviations,
Runout, Tooth Thickness, and Backlash”
and ANSI/AGMA Standards 2015-1-A01
“Accuracy Classification System—
Tangential Measurements for Cylindrical
Gears” with permission of the publisher,
American Gear Manufacturers Association,
500 Montgomery St., Suite 350,
Alexandria, Virginia 22314-1500.
ABOUT THE AUTHOR:
Dennis Gimpert is president of North
American operations for Jos. Koepfer &
Sohne GmbH of Furtwangen, Germany.
He holds a bachelor’s degree from
Michigan Technological University and
has worked as an application engineer
for the machine tool division of Barber
Colman and as vice president of market-
ing for American Pfauter. Gimpert is
active with the American Gear
Manufacturers Association, a member of
the AGMA Board of Directors, and chair-
man of the Business Management
Executive Committee.
38 GEAR SOLUTIONS • JUNE 2005 • gearsolutionsonline.com
