Gear Inspection Reference Manual GM Gear Inspection ISO Addendum January, 2008
Aug 28, 2015
Gear Inspection Reference Manual
GM Gear Inspection ISO Addendum January, 2008
Table of Contents
Introduction 1
Definitions of Primary 2 Gear Tooth Elements
Analytical Gear Inspection 6
Radial Composite Testing 18
Gear Troubleshooting 23 Guide
Page 1
Introduction
Gear quality is specified on the engineering drawing in terms of two types of inspection methods.
Analytical gear inspection CNC equipment checks the following characteristics:
Helix Profile (or involute) Pitch (or index)
Radial Composite (Functional) testing This type of measurement requires a master gear to roll in double flank contact with a workpiece.
This manual is designed to explain the results of these types of inspection methods, and present possible solutions to manufacturing problems as noted on the results.
Page 2
Definitions of Primary Gear Tooth Elements
Flank The flanks of gear teeth are defined as right or left. With reference face I facing you, tooth tip up, the right flank is on the right, and the left flank is on the left.
Right FlankLeft FlankCrest (Tip)
Internal Gear
Reference Face "I"
Left Flank Right Flank
Crest (Tip)
External GearReference Face "I"
Page 3
Root (Minor )
Tip (Major ) Reference (Pitch )
External Gear
Tip (Minor )Reference
(Pitch )
Root (Major )
Internal Gear
Definitions of Primary Gear Tooth Elements (Cont.)
Root and Tip Diameters The diameter at the tip of the gear tooth is the TIP DIAMETER, formerly called the major diameter for external gears. The ROOT DIAMETER was formerly called the minor diameter.
Page 4
Definitions of Primary Gear Tooth Elements (Cont.)
Helix Helix is the angle of the gear teeth relative to the axis of rotation.
Hand Helical gears have either a right or left hand helix. When looking at the end of a tooth closest to you, a right hand helix will clock to the right, while a left hand part will clock to the left as you look farther down the tooth away from you.
Right Hand Helix
Left Hand Helix
Page 5
Definitions of Primary Gear Tooth Elements (Cont.)
ATTENTION! The ISO system is based on HELIX deviations, NOT lead deviations. This is opposite from the GM 1989 inspection standard. However, this is the same convention as the GM DIN based prints.
Profile (Involute) The profile is the involute shape of the gear tooth from the root to the tip.
Pitch Pitch is the distance along the reference circle from one tooth to the next tooth.
Page 6
f H
eva
luatio
n ra
nge
( L
)
Helix slope deviation
face
w
idth
(b)
Analytical Gear Inspection
Helix Slope Deviation (f) HELIX slope deviation is the amount of deviation from a nominal helix over the evaluation range.
Page 7
LeftFlank
RightFlank
(-) (+) (-) (+)
Right Hand Helix
Analytical Gear Inspection (Cont.)
ATTENTION! The ISO system is based on HELIX deviations, NOT lead deviations. This is opposite from the GM 1989 inspection standard. However, this is the same convention as the GM DIN based prints.
For a right hand helix, if the measured helix is more right, the measured value is positive.
If the measured helix is more left, the measured value is negative.
Right Hand Helix
Page 8
LeftFlank
RightFlank
(+) (-) (+) (-)
Left Hand Helix
Analytical Gear Inspection (Cont.)
For a left hand helix, if the measured helix is more right, the measured value is negative.
If the measured helix is more left, the measured value is positive.
Left Hand Helix
Page 9
Analytical Gear Inspection (Cont.)
Interpreting Helix Slope Deviation The analyzed value of the helix slope deviation (fH) represents the difference of the slope as plus or minus from the nominal zero slope line for the specified helix.
For example, given a right hand helix, a plus (positive number) slope deviation on the helix chart from an analytical gear checker indicates that the helix is higher, or further to the right, than nominal. A minus (negative number) slope deviation indicates a helix that is lower or more left than nominal.
Note that the slope deviation value is not a variation in the actual helix angle, but a linear deviation in millimeters across the analyzed zone of the face width.
Mean Helix Slope Deviation (f) Mean helix slope deviation is the average of the helix slope values from the measured teeth. Four teeth are typically measured.
Helix Slope Variation (fv) Helix slope variation is the range of the individual helix slope values, that is, the maximum value minus the minimum value.
Page 10
C
eva
lua
tion
ra
nge
(L
)
Helix crowning
face
w
idth
(b)
Analytical Gear Inspection (Cont.)
Helix Crowning (C) Helix crowning is the distance from the best fit curve to the slope deviation line. This was formerly called lead crown.
Mean Helix Crowning (C) Mean helix crowning is the average of the crown values of the measured teeth.
Helix Crowning
Page 11
f f
eva
lua
tion ra
nge
(L
)
Helix form deviation
face
wid
th (b)
Analytical Gear Inspection (Cont.)
Helix Form Deviation (f) Helix form deviation is the divergence from a best fit curve along the helix. This was formerly called lead irregularity.
Helix Form Deviation
Page 12
f H
eva
lua
tion
ra
nge
(L
)
- +
End ofevaluation
Profile slope deviation
SAP
Analytical Gear Inspection (Cont.)
Profile Slope Deviation (f) Profile slope deviation is the amount of deviation from a nominal involute profile over the evaluation range.
Profile Slope Deviation
Page 13
Analytical Gear Inspection (Cont.)
Mean Profile Slope Deviation (f) Mean profile slope deviation is the average slope of the measured teeth.
Profile Slope Variation (f) Profile slope variation is the range of the individual profile slope values, that is, the maximum value minus the minimum value.
Page 14
C
eva
lua
tion ra
nge
(L
)- +
Profile barreling
End ofevaluation
SAP
Analytical Gear Inspection (Cont.)
Profile Barreling (C) Profile barreling is the distance from the best fit curve to the slope deviation line. This was previously called profile or involute crown.
Mean Profile Barreling (Cm) Mean profile barreling is the average of profile barreling values (C).
Profile Barreling
Page 15
f f
eva
lua
tion
ra
nge
(L
)
- +
Profile form deviation
End ofevaluation
SAP
Analytical Gear Inspection (Cont.)
Profile Form Deviation (ff) Profile form deviation is the divergence of the measured profile from a best fit curve.
Profile Form Deviation
Page 16
1 32 4 65 12117 98 181710 13 14 15 16Pitch Nr.
Flank Nr.118 2 3 4 5 14 15 16 17 186 9 10 11 13127 8
+3 +1 +3 +2
-3 -3
0
-3-2
-4
+1
-3
-1 -1+2 +3 +5
-1
m
fpt diagram
1 32 4 65 12117 98 181710 13 14 15 16Pitch Nr.
Flank Nr.118 2 3 4 5 14 15 16 17 186 9 10 11 13127 8
+3 +1 +3 +2
-3 -3
0
-3-2
-4
+1
-3
-1 -1+2 +3 +5
-1
m
1 32 4 65 12117 98 181710 13 14 15 16Pitch Nr.
Flank Nr.118 2 3 4 5 14 15 16 17 186 9 10 11 13127 8
+3 +1 +3 +2
-3 -3
0
-3-2
-4
+1
-3
-1 -1+2 +3 +5
-1
m
fpt diagram
1 32 4 65 12117 98 181710 13 14 15 16Pitch Nr.
Flank Nr.118 2 3 4 5 14 15 16 17 186 9 10 11 13127 8
m
Fpk diagram
Fp
1 32 4 65 12117 98 181710 13 14 15 16Pitch Nr.
Flank Nr.118 2 3 4 5 14 15 16 17 186 9 10 11 13127 8
m
Fpk diagram
Fp
Analytical Gear Inspection (Cont.)
Single Pitch Deviation (fpt) Single pitch deviation is the difference between the measured pitch and the theoretical pitch value.
Cumulative Pitch Deviation (Fpk) Cumulative pitch deviation is the continuous summation of the single pitch deviations.
Total Cumulative Pitch Deviation (Fp) Total cumulative pitch deviation is the difference between the maximum and minimum cumulative pitch deviations.
Page 17
Analytical Gear Inspection (Cont.)
Runout (F) There are several methods used to determine radial runout.
From a pitch measurement, radial runout can be calculated.
It is also possible to measure radial runout directly using a ball of the appropriate diameter and checking every space for radial deviation.
ATTENTION: Runout determined by analytical inspection is NOT a direct substitute for Runout by Composite Test.
Page 18
Master Gear
ProductionGear
center distancevariation
Radial Composite Testing
Radial Composite Testing Radial composite deviations are determined by placing a product (test) gear in radial double flank contact with a master gear. As the product gear is rotated through one revolution, the change in center distance between the two gears is measured.
From the measurement data, a number of analyses can be made to assess the quality of the gear.
Page 19
F
Radial Composite Deviations (Cont.)
Runout by Composite Test Runout, as it pertains to radial composite deviations, is the difference between the maximum and minimum values of a low pass filtered center distance measurement. This method of determining double flank runout captures both deviations from eccentricity and circularity (out of roundness).
Page 20
f
Radial Composite Deviations (Cont.)
Eccentricity (f) Eccentricity is half the total amplitude of a single sine wave fit to the filtered center distance measurement.
Page 21
f
Radial Composite Deviations (Cont.)
Circularity Circularity is the difference between the maximum and minimum values of the filtered center distance measurement after the eccentricity has been removed.
Page 22
Radial Composite Deviations (Cont.)
Mean Tooth-to-Tooth Radial Composite Deviation Mean tooth-to-tooth redial composite deviation is the average change in center distance due only to tooth action of un-damaged teeth.
Nick A nick (damaged tooth) is a large isolated tooth-to-tooth deviation in excess of the underlying tooth action.
Additional Evaluations The following measurements may also be available on many double flank testers. These measurements can be used for process control but are only approximations. As such, these should not be used for finished part acceptance.
Dimension Over Balls (D.O.B.) Dimension Between Balls (D.B.B.) FTT (Functional Tooth Thickness) Sectional Runout Helix Variation Helix Average Left/Right Flank Helix Slope Taper Taper Average
Page 23
Troubleshooting
Reading the charts
The shape and pattern reveal information about the process that suggests potential causes.
Page 24
Two high and low points signifies out of round or egg shaped gear
Abrupt step means index error between first and last tooth such as with shaping process or measuring error
Tooth to tooth abrupt peak means problem with single tooth or a few adjacent teeth.
Random variation pattern means multiple tooth problems or problems with testing equipment
Straight line may indicate a measurement problem
Page 25
Diameters Tip (major) Minimum chamfer Reference (d) SAP (start of active profile) Base Root (minor)
How composite data is specified on the print:
Size Measurements
Size over pins or balls
Page 26
Gear Troubleshooting Guide
Gear
Elem
ent
Categ
ory
Runout
Total
Com
posite
Tooth
to T
ooth
Nicks
Chara
cteristics
Insp
ectio
n
chart
appe
ara
nce
Hobbed/checked
off
cente
r
Possible
conta
minatio
n
Profile
erro
r
Mesh
interfe
rence
Possible
root
cause
Verify
tooling
(radial ru
nout)
Verify
Maste
r
Check fo
r in
volute
erro
r
Check fo
r plus
tip
Corre
ctive
actio
n
Page 27
Helix
Gea
r
Elem
ent
Categ
ory
Slope (A
ngle)
erro
r
Variatio
n
(wobble)
Form
or
wavin
ess
Ch
ara
cteristics
Insp
ection
chart
appea
ran
ce
Input
correctio
n
needed o
n m
achine
Chips o
n fixtu
re o
r
workh
olding
misalig
ned (a
xial
runout)
Chips o
n cutte
r edge
Cutting
force
to high
Po
ssible ro
ot
cau
se
Input
correctio
n
Verify
axial
runout
of fixtu
re
wea
r
Inspect cutte
r
Verify
workh
olding
rigidity
Co
rrective
action
Page 28
Involute
(profile)
Gea
r
Elem
ent
Categ
ory
Angle
(slope)
erro
r
Variatio
n
(runout)
Form
or
wavin
ess
Ch
ara
cteristics
Insp
ection
chart
appea
ran
ce
Hob
rake a
ngle e
rror
Radial
runout
of gea
r
Cutte
r m
ounting
erro
r
Excessive
finish stock
Worn
tool
Po
ssible ro
ot
cau
se
Check h
ob
sharpe
ning
Check w
orkpiece
and
fixture
runout
Check h
ob
mounting
and
quality
Check stock
rem
oval
amount
Co
rrective
action
Page 29
Pitch
(index)
Gea
r
Elem
ent
Categ
ory
Pitch
(symbol
fp )
Index (total
accu
mulated
pitch e
rror-
symbol
Fp )
Ch
ara
cteristics
Insp
ection
chart
appea
ran
ce
Runout
of p
roductio
n
fixture
or inspectio
n
arb
or
Thread
erro
r o
n h
ob
Wea
r o
r chips
on
broach
bar
Po
ssible ro
ot
cau
se
Verify
workh
olding
Inspect h
ob fo
r
thread
erro
r
Clean chips
off
broach
Co
rrective
action
Page 30
Tooth
thickness
Gea
r
Elem
ent
Categ
ory
Size o
ver pin
s
or b
alls
Relative
tooth
thickness
Ch
ara
cteristics
Insp
ection
chart
appea
ran
ce
Tap
ered
hob
Heat
causing
machin
e g
row
th
Hob
swivel
angle
erro
r
Po
ssible ro
ot
cau
se
Check h
ob fo
r
prope
r q
uality
Monito
r cutting
oil
tem
peratu
re
Adjust h
ob swivel
angle
for co
rrect
size o
ver pins
(DOB
or DO
P)
Co
rrective
action
Page 31
Gear Inspection Symbols and Terms
Note: These symbols may not be fully implemented on all gear inspection systems.
Symbol Term
b facewidth
C profile barreling C helix crowning f profile slope deviation f profile form deviation
f mean profile slope deviation f profile slope variation f helix slope f helix form deviation
f mean helix slope deviation fv helix slope variation Fp total cumulative pitch deviation
Fpk cumulative pitch deviation over a sector of k pitches F single pitch deviation F total radial composite deviation F runout f eccentricity
Page 32
Gear Inspection Symbols and Terms (Cont.)
f" tooth-to-tooth radial composite deviation I reference face
L profile evaluation range L helix evaluation range z number of teeth
No Symbol circularity by composite test
No Symbol
mean tooth-to-tooth radial composite deviation
No Symbol Nick (damaged tooth)
No Symbol runout by composite test
Page 33
References
Please reference GM Document 24241147 for gear inspection standards and practices
The following ISO standards and technical reports represent the basis of cylindrical gear inspection for GM Powertrain: ISO 1328-1:1995 Definitions and allowable values of deviations relevant to corresponding flanks of gear teeth. ISO 1328-2:1997 Definitions and allowable values of deviations relevant to radial composite deviations and runout information. ISO TR 10064-1:1992 Inspection of corresponding flanks of gear teeth. ISO TR 10064-2:1996 Inspection related to radial composite deviations, runout, tooth thickness and backlash. ISO 1122-1:1998 Vocabulary of gear terms.
Page 34
Index
Circularity......................................... 21 Cumulative Pitch Deviation......... 16 Eccentricity...................................... 20 Flank .............................................. 2, 22 Form .................................................. 15 Hand .................................................... 4 Helix................. 1, 4, 6, 9, 10, 11, 22, 27 Helix Crowning ............................... 10 Helix Slope......................................... 9 Involute ............................................... 5 Mean Helix Slope ............................. 9 Nick .................................................... 22 Pitch..................................... 1, 5, 16, 29 Profile ................ 1, 5, 12, 13, 14, 15, 26 Profile Barreling ............................. 14 Radial Composite 1, 3, 18, 19, 20, 21,
22 Radial Composite Testing ........... 18 Root ..................................................... 3 Runout ...................... 17, 19, 22, 26, 29 Runout (F)....................................... 17 Single Pitch Deviation .................. 16 Slope........................ 6, 9, 12, 13, 22, 27 Tip ........................................................ 3 Tooth-to-Tooth................................ 22 Total Cumulative Pitch Deviation
........................................................ 16 Variation ........................................... 13
Page 35
Notes
Page 36
Notes