GM Gear Inspection Handbook ISO DRAFT FINAL

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

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.

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"

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.


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


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.

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.

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

LeftFlank

RightFlank

(+) (-) (+) (-)

Left Hand Helix


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


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.

C

eva

lua

tion

ra

nge

(L

)

Helix crowning

face

w

idth

(b)


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

f f

eva

lua

tion ra

nge

(L

)

Helix form deviation

face

wid

th (b)


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

f H

eva

lua

tion

ra

nge

(L

)

- +

End ofevaluation

Profile slope deviation

SAP


Profile Slope Deviation (f) Profile slope deviation is the amount of deviation from a nominal involute profile over the evaluation range.

Profile Slope Deviation


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.

C

eva

lua

tion ra

nge

(L

)- +

Profile barreling

End ofevaluation

SAP


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

f f

eva

lua

tion

ra

nge

(L

)

- +

Profile form deviation

End ofevaluation

SAP


Profile Form Deviation (ff) Profile form deviation is the divergence of the measured profile from a best fit curve.

Profile Form Deviation

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


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.


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.

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.

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).

f


Eccentricity (f) Eccentricity is half the total amplitude of a single sine wave fit to the filtered center distance measurement.

f


Circularity Circularity is the difference between the maximum and minimum values of the filtered center distance measurement after the eccentricity has been removed.


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

Troubleshooting

Reading the charts

The shape and pattern reveal information about the process that suggests potential causes.

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

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

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

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

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

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

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

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

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

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.

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

Documents

GM Gear Inspection Handbook ISO DRAFT FINAL