AGMA 1102-A03

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ANSI/AGMA 1102--A03

(Revision of AGMA 120.01)

Reaffirmed March 2010

American National Standard

Tolerance Specification forGear Hobs

A N S I / A G M A

1 1 0 2 - - A 0 3

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ii

Tolerance Specification for Gear Hobs ANSI/AGMA 1102--A03[Revision of AGMA 120.01 (1975)]

Approval of an American National Standard requires verification by ANSI that the require-

ments for due process, consensus, and other criteria for approval have been met by the

standards developer.

Consensus is established when, in the judgment of the ANSI Board of Standards Review,

substantial agreement has been reached by directly and materially affected interests.

Substantial agreement means much more than a simple majority, but not necessarily una-

nimity. Consensus requires that all views and objections be considered, and that a

concerted effort be made toward their resolution.

The use of American National Standards is completely voluntary; their existence does not

in any respect preclude anyone, whether he has approved the standards or not, from

manufacturing, marketing, purchasing, or using products, processes, or procedures not

conforming to the standards.

The American National Standards Institute does not develop standards and will in no

circumstances give an interpretation of any American National Standard. Moreover, noperson shall have the right or authority to issue an interpretation of an American National

Standard in thename of the American National StandardsInstitute. Requests forinterpre-

tation of this standard should be addressed to the American Gear Manufacturers

Association.

CAUTION NOTICE: AGMA technical publications are subject to constant improvement,

revision, or withdrawal as dictated by experience. Any person who refers to any AGMA

technical publication should be sure that the publication is the latest available from the

Association on the subject matter.

[Tables or other self--supporting sections may be referenced. Citations should read: SeeANSI/AGMA 1102--A03, Tolerance Specification for Gear Hobs, published by theAmerican Gear Manufacturers Association, 500 Montgomery Street, Suite 350,Alexandria, Virginia 22314, http://www.agma.org.]

Approved December 11, 2003

ABSTRACT

The purpose of this standard is to provide specifications for nomenclature, dimensions, tolerances, andinspection of gear hobs, and thereby establish a basis for mutual understanding in this respect in the use and

manufacture of these tools.

Published by

American Gear Manufacturers Association500 Montgomery Street, Suite 350, Alexandria, Virginia 22314

Copyright © 2003 by American Gear Manufacturers AssociationAll rights reserved.

No part of this publication may be reproduced in any form, in an electronicretrieval system or otherwise, without prior written permission of the publisher.

Printed in the United States of America

ISBN: 1--55589--816--5

AmericanNationalStandard

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ANSI/AGMA 1102--A03AMERICAN NATIONAL STANDARD

iii© AGMA 2003 ---- All rights reserved

Contents

Page

Foreword iv. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1 Scope 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2 Normative references 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3 Terminology and definitions 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4 Hob classifications, drawings, and identification markings 6. . . . . . . . . . . . . . . .

5 Manufacturing and purchasing considerations 8. . . . . . . . . . . . . . . . . . . . . . . . . .6 Gear hobs – single and multiple start – accuracy requirements 12. . . . . . . . . . .

7 Measuring methods and practices 13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Annexes

A Gear manufacturing terminology 33. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

B Hob design parameters 35. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

C Equations and terminology for straight -- sided hob profiles 37. . . . . . . . . . . . . . .

D Intermediate values for multiple thread tolerance calculations 43. . . . . . . . . . . .

E Effects of hob accuracy on gear accuracy 45. . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Figures

1 Hob nomenclature 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 Cam 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3 Engagement zone 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4 Protuberance on a gear hob tooth 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5 Negative rake 5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

6 Positive rake 5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

7 Zero rake 5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

8 Tip relief on a gear tooth 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

9 Normal section 7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Tables

1 Hob markings 8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2 Reference for measurement methods 9. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 Accuracy requirements 20. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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ANSI/AGMA 1102--A03 AMERICAN NATIONAL STANDARD

iv © AGMA 2003 ---- All rights reserved

Foreword

[The foreword, footnotes and annexes, if any, in this document are provided for

informational purposes only and are not to be construed as a part of ANSI/AGMA Standard

1102--A03, Tolerance Specification for Gear Hobs.]

ANSI/AGMA 1102--A03 is a replacement of AGMA 120.01. The first draft of AGMA 120.01

was prepared by the Cutting Tools Committee in May, 1972. Its purpose was to consolidate

all AGMA standards relating to hobs; i.e., AGMA 121.02, 122.02, 123.01 and 124.01. Thepurpose of consolidating these standards was to provide the information as a handy

updated reference on gear--cutting tools for efficient use by manufacturers and users of

these tools.

The committee decided at the 1972 Semi--Annual Meeting to include Standard 124.01,

Wormgear Hobs , as an Information Sheet. AGMA 120.01 was approved by the Cutting

Tools Committee on November 6, 1973. It was approved by the AGMA Membership as of

February 28, 1975.

ANSI/AGMA 1102--A03 is theresultof a rewrite of AGMA 120.01,incorporation of themetric

system, addition of inspection procedures, and development of equation based tolerances.

Other additions include increased tolerance grade levels, expansion of tolerances for

multi--thread hobs, line of action testing, and expansion of the hob range of sizes.The first draft of AGMA 1102--A03 was made in February, 1999. It was approved by the

AGMA membership in October, 2003. It was approved as an American National Standard

on December 11, 2003.

Suggestions for improvement of this standard will be welcome. They should be sent to the

American Gear Manufacturers Association,500 Montgomery Street, Suite 350, Alexandria,

Virginia 22314.

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v© AGMA 2003 ---- All rights reserved

PERSONNEL of the AGMA Cutting Tools Committee

Chairman: Michael Tennutti Star--SU, Inc./Star Cutter Company. . . . . . . . . . . . . . . . . . . . . . . . . .

ACTIVE MEMBERS

C. Awot Koepfer America, L.L.C.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

T.R. Blum Gleason Works. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .J. Brunner Falk Corporation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

J.V. Caldwell SU America, Inc.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

D. Hoying M&M Precision Systems Corporation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

E. Lawson M&M Precision Systems Corporation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

S. Lyncha Horsburgh & Scott Company. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

W. Miller GearHelp LLC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

R.P. Phillips Gleason Cutting Tools Corporation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

ASSOCIATE MEMBERS

A.S. Cohen Engranes y Maquinaria Arco, S.A.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

J.S. Cowan Eaton Corporation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

M.E. Cowan Process Equipment Company. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

M. Denipoti SU America, Inc.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

D. Drechsler Huffman Corporation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

D.W. Goodfellow SU America, Inc.. . . . . . . . . . . . . . . . . . . . . . . . . .

H. Hagiwara Nippon Gear Copmany, Ltd.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

W. Hayward Fairfield Manufacturing Company, Inc.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

W.E. Lake Mitsubishi Gear Technology Center. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

R. Mory Ford Motor Company. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

W. Norberg Columbia Gear Corporation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

B. Nyamagoudar SU America, Inc.. . . . . . . . . . . . . . . . . . . . . . . . . .D. Palmer Brad Foote Gear Works, Inc.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

T. Royer M&M Precision Systems Corporation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

J. Rybak Technical University of Rzeszow. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

D. Sine Nachi Machining Technology Company. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

L.J. Smith Consultant. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

R.E. Smith R.E. Smith & Company, Inc.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

T. Ware Star SU, Inc./Star Cutter Company. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

M. Woodhouse Star SU, Inc./Star Cutter Company. . . . . . . . . . . . . . . . . . . . . . . . . . . .

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vi © AGMA 2003 ---- All rights reserved

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1© AGMA 2003 ---- All rights reserved


American National Standard --

Tolerance Specificationfor Gear Hobs

1 Scope

This standard provides specifications for nomencla-

ture,dimensions,tolerances,and inspection for gear

hobs for modules 0.63 to 40 mm. It establishes abasis for understanding the use and manufacture of

these tools.

1.1 Application

This standard applies to single and multiple--thread

hobs for spur and helical gears.

1.2 Exceptions

This standard is not intended to completely define

the hob tooth profile as it relates to the exact gear

profile. It is advisable to check gear tooth profilespecifications with the hob manufacturer involved.

Examples includecutting depth and hob tooth profile

modification as they affect gear tooth tip relief for

fine--pitch and coarse--pitch hobs.

Where conditions require use of hobs of special

design or specifications, such hobs shall be

considered beyond the scope of this standard.

2 Normative references

The following standards contain provisions which,

throughreference in this text,constitute provisionsof

this American National Standard. At the time of

publication, the editions indicated were valid. All

standards are subject to revision, and parties to

agreements based on this American National Stan-

dard are encouraged to investigate the possibility of

applying the most recent editions of the standards

indicated below.

ANSI/AGMA 1012--F90, Gear Nomenclature,

Definitions of Terms with Symbols

AGMA 915--3--A99, Inspection Practices -- Gear

Blanks, Shaft Center Distance and Parallelism

MIL--STD--105D, Sampling Procedures and Tables

for Inspection by Attributes

3 Terminology and definitions

The terms and definitions used in this standard are,

wherever possible, consistent with ANSI/AGMA

1012--F90 and other approved AGMA documents.

However, some symbols and definitions used in this

standard may differ from other AGMA Standards.

Users should assure themselves that they fully

understand the terms, definitions, and symbols as

contained in this standard.

Nomenclature used in this standard and the hob

elements referred to are illustrated in figure 1.

Nomenclature of hob elements and other terms

relating to hobbing are presented as follows:

active hob length: axial length of the toothedportion of the hob.

allowed deviation: maximum deviation a hob can

have without exceeding the tolerance.

auxiliary leads: feature employed in some hobs,

especially worm gear hobs, wherein both sides of the

hob thread have leads differentfrom the nominal hob

lead; one side longer, the other side shorter. This

results in thetooththickness being successively less

toward the roughing end of the hob.

axial plane: plane containing the axis of rotation.

axial pressure angle: see definition under

pressure angle.

back--off: see preferred term cam relief, under

relief.

bore diameter: diameter of the mounting hole for

arbor type hobs.

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2 © AGMA 2003 ---- All rights reserved

LeadangleR.H.

Outside

diameter Pitch

cylinderdiameter

Hubdiameter

Length

See figure 9

Toothface

Borediameter

Axial pitch

Axial lead

Multiplethreads

Flutehelix angle

Figure 1 -- Hob nomenclature

bore diameter: diameter of the mounting hole for

arbor type hobs.

cam: radial drop of the form in the angular distance

between adjacent tooth faces. See figure 2.

Cam

Figure 2 -- Cam

cam relief: see definition under relief.

chamfer: beveled surface to eliminate an otherwise

sharp corner.

clutch keyway: see face keyway.

depth of cut: radial depth to which the hob is sunk

into the workpiece. See related term whole depth.

deviation: differences observed during testing that

are compared against the specified value or toler-

ance.

engagement zone: axial distance within which the

hob interacts with the involute portion of a gear tooth

profile being generated. It is equal to the axial

component of the hob line of action within the

confines of the functional profile. See figure 3.

Involute generatingpath of engagement Line of

action

functionalprofiledepth

engagementzone

Figure 3 -- Engagement zone

evaluation zone: full toothed portion of the hob.

face keyway: transverse slot across the hub face.

fillet: 1) curved line joining two lines to eliminate a

sharp internal corner; 2) curved surface joining two

surfaces to eliminate a sharp internal corner.

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flute: longitudinal groove, either straight or helical,

that forms the tooth face of one row of hob teeth and

the backs of the preceding row.

flute helix angle: angle which a helical tooth face

makes with an axial plane, measured on the hob

pitch cylinder.

flute index: see tooth face index.

flute lead: axial advance of a flute face in one turn

around the axis of a hob.

flute lead deviation: deviation of a hob tooth face

from the desired helical surface.

full tipradius: continuous radius tangent to top and

side cutting edges.

functional profile: portion of hob tooth that

generates the involute profile of a gear tooth. It is

limited toward the tip by the start of tip radius or,

when present, start of protuberance modification. Itis limited toward the root by the hob tooth dedendum

or, when present, start of tip relief or chamfer

modification. See figure 3.

functional profile depth: depth of the functional

profile.

gash: see preferred term flute.

generated fillet: at the bottom of the hobbed form,

fillet joining the root diameter with the desired

generated form. This fillet is not a true radius

(trochoid form).

generated fillet height: on the hobbed workpiece,

radial distance from the root diameter to the point

where the generated fillet joins the desired gener-

ated form.

helicoid, Archimedes: plane surface of compound

curvature, defined by its intersections with the

following planes:

-- intersection with a transverse plane is an

Archimedes spiral;

-- intersection with a concentric cylinder is a

helix;

-- intersection with an axial plane is a straight

line.

helicoid, involute: plane surface of compound

curvature, defined by its intersections with the

following planes:

-- intersection with a transverse plane is an

involute curve;

-- intersection with a concentric cylinder is a

helix;

-- intersection with a plane of action is a straight

line.

hob addendum: radial distance between the top of

the hob tooth and the pitch cylinder (gear

dedendum).

hob dedendum: in topping hobs, radial distancebetween the bottom of hob tooth profile and pitch

cylinder (gear addendum).

hob full --topping: hob that cuts the gear outside

diameter and chamfers the gear tooth tip.

hob, non--topping: hob that does not cut the

outside diameter of the gear.

hob, topping: hob that cuts the gear outside

diameter.

hob runout: runout of the hob when mounted in ahobbing machine, measured radially on hub

diameter, and axially on hub face.

hob, semi --topping: hob that produces a chamfer

or tip relief on the gear.

hob teeth in engagement zone: within a given

thread, the approximate number of hob teeth

included in the engagement zone. This is also the

number of teeth involved in generating the involute

portion of the gear tooth profile. See figure 3.

hob tip modification: modification on the sides ofthe hob tooth near the top.

hob tooth depth: minimum active depth of hob

tooth form.

hook: see preferred term rake.

hub: qualifying surface at each end of an arbor type

hob which is provided for checking diameter and

face runout. On a shank style hob, it is the clamping

surfaces or proof bands, when available.

hub diameter runout: total deviation in radialdistance of the hub periphery from the axis.

hub face: side surface of the hub.

hub face runout: total axial deviation of the hub

face from a true plane of rotation.

key: mechanical member through which the turning

force is transmitted to the hob.

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keyway: slot through which the turning force is

transmitted to the hob. May be either a longitudinal

slot through the hole or a transverse slot across the

hub face. If the latter, it is called a face keyway.

lead: axial advance of a thread for one complete

turn or convolution.

lead angle: angle between any helix and a plane of

rotation,. In a hob, lead angle usually refers

specifically to the angle of thread helix measured on

the pitch cylinder.

lead deviation: axialdeviationof the hob teeth from

the correct thread lead.

length: total distance from one end to the other

including shanks and hubs.

normal circular pitch: see definition under pitch.

normal module: π (pi) times the normal circular

pitch.

normal plane: plane perpendicular to a pitch

cylinder helix.

normal pressure angle: see definition under

pressure angle.

number of threads: in multiple thread hobs,

number of parallel helical paths along which hob

teeth are arranged, sometimes referred to as

number of starts.

observed: Measuring of actual differences through

testing.

offset: see preferred term rake offset.

outside diameter: diameter of the cylinder which

contains the tops of the cutting edges of the hob

teeth.

outside diameter runout: total deviation in the

radial distance from the axis to the tops of the hob

teeth.

pilot end: on shank type hobs, cylindrical or conical

bearing surface opposite the driving end.

pitch: distance between corresponding, equally

spaced hob thread elements along a given line or

curve. Use of the single word pitch without

qualification may be confusing. Specific terms such

as normal circular pitch or axial pitch are pre-

ferred.

pitch, axial: pitch parallel to the axis in an axial

plane between corresponding elements of adjacent

hob thread sections. Use of the term axial pitch is

preferred to the term linear pitch.

pitch, base: pitch on the base circleor along the line

of action.

pitch, normal circular: distance between corre-

sponding elements on adjacent hob thread sections

measured along a helix that is normal to the thread

helix in the pitch cylinder.

pitch circle: transverse section of the hob pitch

cylinder.

pitch cylinder: reference cylinder in a hob from

which design elements, such as lead, lead angle,

and tooth thickness are derived.

pitch diameter: diameter of the pitch cylinder.

pitch point: point at which a tooth profile intersectsthe pitch cylinder.

pressure angle: angle between a tooth profile anda

line perpendicular to the pitch cylinder at the pitch

point. In hobs, the pressure angle is usually

specified in the normal plane or in the axial plane.

pressure angle, axial: pressure angle measured in

anaxial plane. Use ofthe term axial pressure angle

is preferred to the term linear pressure angle.

pressure angle, normal: pressureangle measured

in a normal plane.

profile: see functional profile.

protuberance: modification near the top of the hob

tooth which produces undercut at the bottom of the

tooth of the workpiece. See figure 4.

ProtuberanceAmount of

protuberance

Figure 4 -- Protuberance on a gear hob tooth

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rake: angular relationship between the tooth face

and a radial line intersecting the tooth face at the hob

outside diameter, measured in a plane perpendicu-

lar to the axis.

rake, negative: condition wherein the peripheral

cutting edge lags the tooth face in rotation. See

figure 5.

Negativerake

Rake offset

Figure 5 -- Negative rake

rake, positive: condition wherein the peripheral

cutting edge leads the tooth face in rotation. See

figure 6.

Positiverake

Rake offset

Figure 6 -- Positive rake

rake, zero: condition wherein the tooth face

coincides with a radial line. See figure 7.

Radialtooth face

(zero rake)

Figure 7 -- Zero rake

rake offset: distance between the tooth face and a

radial line parallel to the tooth face. Used for

checking rake. See figures 5 and 6.

ramp: modification at the bottom of the hob tooth

which produces a chamfer at the top corners of the

tooth of the workpiece.

reference diameter: synonymous with the nominal

hob pitch diameter. It is the diameter at which hob

tooth thickness is defined and controlled. It is also,

by convention, the diameter at which various other

hob geometry parameters are evaluated, including

flute lead, flute index, and thread lead.

relief: result of the removalof tool material behind or

adjacent to a cutting edge to provide clearance and

prevent rubbing (heel drag).

relief, cam: relieffrom the cutting edges to the back

of the tooth produced by a cam actuated cutting tool

or grinding wheel on a relieving (back--off) machine.

relief, side: relief provided at the sides of the teeth

behind the cutting edges. The amount depends

upon the radial relief, axial relief, and nature of the

tooth profile.

root diameter: in topping hobs, the outside

diameter minus (2) whole depths.

shank: projecting portion of a hobwhich locates and

drives the hob in the machine spindle or adapter.

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short (or long) lead: special design wherein the

hob lead is made shorter (longer) than the normal or

theoretical lead, to generate at a lower (higher)

diameter on the workpiece, to meet a particular fillet,

undercut or generating requirement.

side relief: see definition under relief.

stock allowance: amount of a modification of the

hob tooth to leave material on the workpiece tooth

form for subsequent finishing.

thread: a helical ridge, generally of constant form or

profile. Ina hob, unlikea worm orscrew, the threadis

not continuous and exists only at thecutting edges of

the hob teeth. Therefore, it is sometimes referred to

as the thread envelope.

thread envelope: see preferred term thread.

thread helix: helix of the hob thread in the pitch

cylinder.

thread spacing: difference in the average devi-

ations obtained by traversing along the desired

helical path of one thread, indexing and traversing in

a similar manner on another thread.

tip radius: radiusofthearcjoiningthetopandaside

cutting edge of a hob tooth.

tip relief: gear tooth modification in which a small

amount of material is removed from the basic profile

near the tip of the gear tooth. See figure 8.

tip relief modification: modification on the sides of

the hob tooth near the bottom which produces tip

relief on the gear tooth.

Tip relief

Amount oftip relief

Start oftip relief

Figure 8 -- Tip relief on a gear tooth

tooth: projection on a hob which carries a cutting

edge.

tooth face: tooth surface against which the chips

impinge.

tooth face index: deviation from the desired

position between tooth faces measured in the plane

of rotation.

tooth thickness: actual width or thickness of the

hob tooth at the pitch cylinder. Use of the single term

tooth thickness without qualification may be confus-

ing. The specific terms normal tooth thicknessand

axial tooth thickness are preferred.

tooth thickness, axial: tooth thickness as mea-

sured in an axial plane.

tooth thickness, normal: tooth thickness as

measured along a helix normal to the thread helix.

whole depth: radial depth which the hob is

designed to produce on the workpiece.

4 Hob classifications, drawings, and iden-tification markings

4.1 Coverage

Hobs covered by this standard are classified and

shall be marked with reference to the classification.

4.2 Drawings

This standard enumerates minimum drawing dataand format for conveying information about a hob

design. The minimum informational requirement

should not be construed as precludingmore detailed

data from being presented on a hob drawing.

4.2.1 Normal section

The tooth form on the hob shall be illustrated on the

hob drawing in the normal plane and in such an

attitude as having the tooth face top coming.

Minimum dimensioning in the normal section shall

include:

-- normal circular pitch;

-- normal pressure angle;

-- nominal hob tooth design;

-- normal tooth thickness;

-- hob addendum (a basic dimension at which

the tooth thickness has been specified).

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Where there are modifications to the functional

profile of thehob, thefollowing additional information

shall also be shown on the normal section to define

the range for profile inspection:

-- depth to tip relief modification

-- depth to hob tip modification

4.2.2 Standard format

Figure 9 illustrates the standard format to be used to

present the normal section dimensions.

4.2.3 Minimum hob data

Minimum hob data listed on thedrawing shall include

the hob’s elements as follows:

4.2.3.1 Physical data

-- bore diameter or shank diameter;

-- nominal outside diameter;

-- nominal hub diameter;

-- nominal hub width;

-- keyway depth;

-- keyway width;

-- nominal length.

4.2.3.2 Lead data

-- number of threads;

-- lead (axial);

-- hand of lead.

4.2.3.3 Flute data

-- number of flutes;-- flute lead;

-- hand of flute lead;

-- rake.

4.2.3.4 General data

-- accuracy grade;

-- nominal cam;

-- normal module.

4.3 Identification

Allhobscovered by this standard shall be markedfor

identification.

4.3.1 Hob markings

As may be appropriate, values for hob elements or

features and standard marking symbols from table 1

are to be used.

Hobaddendum Nominal

hobtooth depth

Circular pitch

Tooththickness

Depth to hobtip modification

Depth to tiprelief modification

Referencediameter

Hobdedendum

(topping only)Pressure angle

Figure 9 -- Normal section

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Table 1 -- Hob markings

Element or feature Standard marking

abbreviations

Normal module xx.xxxx NMOD

Normal pressure angle xx.xxxx NPA

Hob normal modulea) xx.xxxx HNMOD

Hob normal pressure

anglea)xx.xxxx HNPA

Number of threads x THD

Hand of threads x H

Hob tooth depth xx.xxx HTD

Lead angle x.xxx° or x°xx′ LA

Flute leadb) c) x.xx° FL

Positive raked) xx°--xx.xxx RAKE

Negative raked) NEG xx°--xx.xxx RAKE

Class (grade) CL xxx

Pre--shave PRE--S

Pre--roll PRE--RPre--grind PRE--G

Pre--skive PRE--K

Tip mod TPREL

Flank mod FLREL

Full toppinge) F--TOP

Semi--toppinge) S--TOP

Roughing RGH

Finishing FIN

NOTE:a) Only show if different than gear data block value.

b) Do not mark if straight.c) Straight gash may be denoted by ∞FL.d) If not marked, assume “zero” rake offset (not usedin this table).e) If not marked, assume Non--topping (not used inthis table).

4.3.2 Additional hob markings

The following additional markings and identification

shall be considered optional and based on purchas-

er’s or manufacturer’s requirements:

-- purchaser’s tool or part number, or both;

-- manufacturer’s code, or serial number;

-- hob material identification;

-- setting angle;

-- date of manufacture.

5 Manufacturing and purchasingconsiderations

This standard provides classification tolerances and

measurement methods for gear hobs. This clause

presents considerations for control of the various

phases of hob manufacturing, including the

recommended process controls and measurement

methods.

These methods provide the hob manufacturer and

purchaser with recommendations for verifying the

accuracy of a hob, as well as information relative to

the interpretation of measurement data.

Some design and application considerations may

warrant measuring or documentation not normally

available in standard hob manufacturing processes.

Specific requirements are to be stated in the

contractual documents.

In the previous classification system (AGMA

120.01), hob accuracy grades were specified by

letter, ranging from Class D through Class AA, in

order of increasing precision. In this standard,

accuracy grades are also specified by letter, ranging

from grade D through grade AAA, in order of

increasing precision. However, it is important to

understand that the tolerance structures of the two

standards are not related.

5.1 Manufacturing certification

Certification of variations in accordance with the

hob’s specific AGMA accuracy grade and inspection

charts or data can be requested as part of the

purchase contract.

Manufacturing of hobs to a specified accuracy may

or may not include specific measurements. When

applications warrant, it may be necessary to estab-

lish detailed acceptance criteria for a hob including

specifications concerning measurements, data

analysis, and any additional considerations. Specif-

ic methods of measurement, documentation of

accuracy grade, and other geometric tolerances of a

hob are normally considered items that are to be

mutually agreed upon between hob manufacturerand purchaser.

NOTE: Specifying an AGMA hob accuracy grade that

requires closer tolerances than required by the

application may increase cost unnecessarily.

5.2 Process control

Process control is defined as the method by which

hob accuracy is maintained through control of each

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individual step of the hob manufacturing process.

Upon completion of all manufacturing operations, a

specific hob has been given an inherent level of

accuracy; this level of accuracy was established

during the manufacturing process, and is totally

independent of any final inspection.

Process control includes elements such as

manufacturing planning, maintenance of machine

tools, cutting tool selection and maintenance, heat

treatment control, and quality assurance programs,

as needed, to achieve and maintain the necessary

hob accuracy. When properly applied, hobs

manufactured by specific control techniques will be

found to be of very uniformquality. Therefore, little or

no final inspection may be necessary for a hob,

particularly in some accuracy levels; assurance of

the necessary accuracy having been manufactured

through careful control at each step.

NOTE: Documentation may be deemed unnecessary

for hobs manufactured under process control when

inspection records are not specified in the purchase

contract.

With proper application of process control, relatively

few measurements may be made on any one hob.

Hobs made in production quantities may be in-

spected at various steps in their manufacturing

process on a statistical basis. Thus,it is possible that

a specific hob canpass through theentireproduction

process without ever having been measured.However, based on appropriate confidence in the

applied process control, the manufacturer of that

hob must be able to certify that it meets the specified

accuracy level.

5.3 Measurement methods

Hob geometry may be measured by a number of

alternatemethods as shown in table 2. The selection

of the particular method depends on the magnitude

of the tolerance, production quantities, equipmentavailable, and measurement costs.

The manufacturer or purchaser may wish to mea-

sure one or more of the geometric features of a hob

to verify its accuracy grade. However, a hob that is

specified to an AGMA accuracy grade must meet all

applicable individual tolerance requirements. Nor-

mally, the tolerances apply to both sides of the teeth.

When prior agreementbetween thehob manufactur-

er and purchaser specifies measurement of hobs,

the manufacturer may select:

-- the measurement method to be used from

among the applicable methods described in this

standard and summarized in table 2;

-- the piece of measurement equipment to beused by the selected measurement method, pro-

vided it is in proper calibration;

-- the individual teeth to be measured, as long

as they are approximately equally spaced.

NOTE: No particular method of measurement or

documentation is considered mandatory unless specif-

ically agreed upon between hob manufacturer and pur-

chaser. When applications require measurements

beyond those recommended in this standard, special

measurement methods must be negotiated prior to

manufacturing the hob.

Table 2 -- Reference for measurement methods

Test numbera)

Test description esmethod Elemental

tests

Composite

tests

Hub diameterrunout

7.3 1 1

Hub face runout 7.3 2 2

Outside diameterrunout

7.4 3 3

Rake offset 7.7 4 4

Tooth face index,

adjacent 7.5 5 5

Tooth face index,total

7.5 6 6

Flute lead 7.6 7 7

Tooth profile 7.10 8 8A

Tooth thickness 7.11 9 9

Thread lead,adjacent

7.8 10 10

Thread lead in 1axial pitch

7.8 11 11A

Thread lead in 3axial pitches

7.8 12 12

Line of action,

adjacent 7.12 b) 13

Line of action, total 7.12 b) 14

Thread spacing,adjacent

7.9 15 15A

Thread spacing,total

7.9 16 16A

Bore diameter 7.2 17 17

NOTES:a) See clause 6b) Test does not apply for elemental method

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5.3.1 Considerations for hob measurements

Before hob measurement values can be compared

with tolerance values, certain operational parame-

ters of the measurement instrument must be known.

This includes:

-- datum axis;

-- measurement location;

-- direction of measurement;

-- direction of tolerancing;

-- hob geometry system.

In some cases, measurement instruments follow the

minimum requirements by default. When other

conditions exist, it is required that causes of the

resulting measurement differences are known and

compensated.

5.3.1.1 Reference axis

Specification of hob geometry requires definition of

an appropriate reference axis of rotation, called the

reference axis. It is defined by specification of the

reference surfaces. See 7.1.2.

The reference axis determines tooth geometry,

thereby being the reference for measurements and

associated tolerances. See AGMA 915--3--A99.

5.3.1.2 Measurement location

The location of hob measurements can affect both

the resulting values and relevance of those values to

the proper functioning of the hob. Also, measure-

ment locations must be clearly defined if different

measurement operations are to achieve satisfactory

correlation.

The specification of measurement location may

include a number of possible parameters including

diameter, axial position, distance behind the cutting

edge (on the tooth flank), and whether testing is

carried out on the flank or over the cutting edge. Hob

measurements should be carried out at the default

locations specified in this standard. Reports of hob

measurement results must include descriptions of

any test locations that deviate from these default

locations.

Test 1, Hub Diameter Runout, requires specifica-

tion of the axial position of testing. The default

position is one millimeter from the adjacent hub

face.

Test2, Hub Face Runout,requires specification of

the testing diameter. The default position is one

millimeter in from the hub outside diameter.

Test 3, Outside Diameter Runout, requires speci-

fication of the axial position of testing. The default

position is at the centers of the tooth tips, midway

between the cutting edges of each given tooth.

Test 4, Rake Offset, requires specification of theaxial position of testing. The default position is at

the centers of the tooth faces, midway between

the cutting edges of each given tooth.

Tests 5 and 6, Tooth Face Index, require specifi-

cation of the diameter and the axial position of

testing. The default diameter is the reference

diameter as specified in clause 3. The default

axial position is at the centers of the tooth faces,

midway between the cutting edges of each given

tooth.

Test 7, Flute Lead, requires specification of the

testing diameter. The default position is the

reference diameter as specified in clause 3.

Tests 8, 8A, Tooth Profile, require specification of

whether testing is carried out on the flank or over

the cutting edge and, if testing will be on the flank,

the distance behind the cutting edge. The default

is on the flank for test 8 and over the cutting edge

for test 8A.

Test 9, Tooth Thickness, requires specification of

the testing diameter. The default position is the

hob reference diameter as defined in clause 3.

Tests 10, 11, 11A, and 12, Thread Lead, require

specification of the diameter and whether testing

is carried outon the flank or over the cutting edge.

Thedefault position is over thecutting edge, at the

hob reference diameter as defined in clause 3.

Tests 13 and 14, Line of Action, require testing

over the cutting edge.

Tests 15,15a,16 and 16a, Thread Spacing, are

based upon data derived from testing of Thread

Lead. The same measurement location specifi-

cations, as in tests 10 through 12, are therefore

applicable.

Test 17, Bore diameter, requires the specification

of the method of testing.

5.3.1.3 Direction of measurement

Measurements of the shape or the position of any

surface can be made in a direction normal to that

surface or inclined to the surface at some angle.

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Common metrology practice is to measure in a

direction normal to the surface being tested. This

holds true for some hob parameters including hub

faces, hub diameters, and outside diameters. It may

or may not be true for hob flute faces and is rarely

true for all remaining hob tooth parameters. It is

important to understand that various hob measuring

instruments use different testing procedures, some

measuring given parameters in the normal direction,

others measuring in other directions.

If the direction of measurement and direction of

tolerancing are different, original measurement

values must be compensated before test values can

be compared to the tolerances.

5.3.1.4 Direction of tolerancing

Tolerances on the shape or the position of hob

surfaces must specify the direction in which given

measurements are to be considered. This specifieddirection, called the tolerancing direction, may be

normal to that surface or inclined at some angle.

In this standard, the tolerancing direction varies with

the given toleranced parameter. Tolerancing direc-

tion requirements are listed in clause 7. Original

measurement values must be compensated if the

actual measurement direction and the tolerancing

direction specified for the given parameter are

different.

The specified direction of tolerancing for runout of

hub faces is axial and for runout of hub diameters

and outside diameters is radial. The direction of

tolerancing forhob flute face parameters is normal to

those surfaces.

The specified direction of tolerancing for remaining

hob parameters is normal to the involute helicoid

surface approximated by the hob cutting edges. At

any point on a hob tooth surface, that normal vector

is oriented 1) tangent to the base cylinder of the hob,

and 2) inclined relative to the transverse plane at the

base helix angle.

Measurements taken in the tolerance direction have

the following characteristics:

-- Measurements will always be the smallest

when the direction of measurement is normal to

the surface. Measurements at any other inclina-

tion will be larger;

-- Measurements made normal to the involute

helicoid surface approximated by the hob cutting

edges are not affected by the tolerance diameter

selected by the test operator;

-- As the hob proceeds through mesh with the

mating gear, the points of contact between the

hob cutting edges and gear tooth profile occur

along a line of action, which is oriented normal to

theinvolute helicoid tooth surfaces of both thehob

and gear. Measurements reported in this normal

direction coincide with the cutting engagement

between hob and gear teeth. Such hob measure-

ments thus correlate well with normal direction

measurements of the gear tooth profiles pro-

duced by that hob.

5.4 Additional considerations

When specifying a hob, there may be additional or

special considerations such as:

-- modified AGMA accuracy grade;

-- hob geometry system.

These and other special considerations are to be

reviewed and agreed upon by the manufacturer and

purchaser.

5.4.1 Modified AGMA accuracy grade

Conditions may require that one or more of the

individual hob elemental or composite tolerances be

of a lower or higher accuracy grade than the other

tolerances. In suchcases,it is possible to modify the

accuracy grade to include an accuracy grade foreach hob elemental or composite tolerance.

NOTE: Specifying an AGMA hob accuracy grade that

requires closer tolerances than required by theapplica-

tion may increase cost unnecessarily.

5.4.2 Hob geometry system

Hobs may be specified with either involute helicoid

(straight profile in the plane of action) or Archimedes

helicoid (straight profile in the axial plane) geometry

systems. While the involute helicoid system is

technically most correct, the Archimedes helicoidsystem may be used because it is more economical

to produce and, for most applications, the differ-

ences in gear profiles produced are not significant.

See Annex C.

5.5 Acceptance criteria

Tolerances, methods, and definitions contained in

this standard prevail unless contractual agreements

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between manufacturer and purchaser contain spe-

cific exceptions.

5.5.1 Evaluation of hob accuracy

Evaluation of AGMA hob accuracy can be made

either by elemental methods or composite methods,

as listed in table 2, but not both. See 5.1.

Accuracy ofa hobis determined by the lowest AGMAaccuracy grade letter obtained by evaluating thehob

using the criteria of this standard.

6 Gear hobs – single and multiple start –accuracy requirements

6.1 Derivation of tolerances

With the exception of Test 7 (flute lead) and Test 17

(bore diameter), the datum from which all the valuesin table 3 are derived is the value of45 mm in Test 14,

Grade A, module 16--25.

It should be noted that Test 7 (flute lead) and Test 17

(bore diameter) do not conform to a datum value and

are not in the statements below concerning grade

relationships.

6.1.1 Rounding rules

Values determined from the equations in 6.1 through

6.5 are to be rounded to the nearest whole micron

with two microns being the minimum value, with theexception of test 2 where the minimum value is 1

micron.

NOTE: If the measuring instrument reads in inches,

then values calculated in clause 6 are to be converted

to inches and rounded to the nearest fifty millionths of

an inch (0.00005 in).

6.1.2 Grade ratios

The ratios between grades are:

Grade AAA and Grade AA is 1.6 except for Test 9

where it is 1.

Grade AA and Grade A is 1.6, except for Test 9

where it is 1.

Grade A and Grade B is:

1.6 for Tests 1 and 2.

1.8 for Tests 3 to 6.

2 for Tests 8 to 14.

Grade B and Grade C is:

2 for Tests 3, 7, 8 and 10 to 14.

1 for Tests 1, 2, 4, 5, 6, 9.

Grade C and Grade D is 1.32 for all tests except for

bore tolerances, which are in Test 17.

6.1.3 Module range ratios

The ratios between module ranges are:

0.63--1 module and 1--2 module is 1.06

1--2 module and 2--3.5 module is 1.12

2--3.5 module and 3.5--6.3 module is 1.18

3.5--6.3 module and 6.3--10 module is 1.25

6.3--10 module and 10--16 module is 1.32

10--16 module and 16--25 module is 1.40

16--25 module and 25--40 module is 1.444

6.1.4 Test ratios

Test ratios are:

Test 1: Hub diameter; radial runout

Test 14 ÷ 3.15

Test 2: Hub face; axial runout

Test 14 ÷ 4

Test 3: Outside diameter; radial runout of tips

Test 14 x 1.6

Test 4: Tooth faces of gashes; straightness and

radial alignment

Test 14 x 1.25

Test 5: Tooth faces of gashes; adjacent

spacing

Test 14 x 1.6

Test 6: Tooth faces of gashes; cumulative

spacing

Test 14 x 3

Test 7: Flute lead (no relationship to Test 14)

Test 8: Tooth profile over the cutting edge or on

the flank (see 6.5 for multiple thread

profile ratios)

Test 14 ÷ 2

Test 8A: Tooth profile over the cuttingedges (see

notes at end of table and 6.5 for multiple

thread profile ratios )

Test 14 ÷ 1

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Test 9: Tooth thickness

Test 14 x 2.24

Test 10: Thread lead; tooth--to--tooth

Test 14 ÷ 2.24

Test 11: Thread lead; cumulative in one axial

pitch ( see 6.5 for multiple thread profile

ratios)

Test 14 ÷ 1.25

Test 11A:Thread lead; cumulative in one axial

pitch (see notes at end of table and 6.5

for multiple thread profile ratios)

Test 14 ÷ 1.12

Test 12: Thread lead; cumulative in 3 axial

pitches

Test 14 x 1.4

Test 13: Tooth spacing along line of action;

tooth--to--tooth

Test 14 ÷ 2.24

Test 14: Tooth spacing along line of action;

cumulative

Datum: 45 mm, m>16 to 25, Grade A

6.2 Multiple thread ratios

Using the sum of the single thread tolerances for

profile (Test 8, 8A) and lead (Test 11, 11A) in one

axial pitch, the following multipliers are used to

calculate the sum of profile, lead in one axial pitch

and lead thread to thread for multiple thread hobs.

2 threads 1.6

3--4 threads 1.9

5--7 threads 2.2

NOTE: See Annex D for intermediate values.

Multi--thread sum = Single thread sum ¢

[Factor from above]

Test 8, 8A: Tooth profile over cutting edges or

on the flank = 0.3¢

[Multiiple Thread Sum]

Test 11, 11A: Thread lead: cumulative in one axial

pitch = 2/3¢ 0.7¢


Test 15, 15A: Threadspacing adjacent = 1/ 3¢0.7¢


Test 16, 16A: Thread spacing, total= 1.5 ¢

[Adjacent Thread Spacing]

7 Measuring methods and practices

This section describes the recommended methods

and practices to be used for the inspection of gear

hobs. Experienced personnel, using calibrated

instruments in a suitable environment, are required.

No particular method of inspection or documentation

is considered mandatory unless specifically agreed

upon between hob manufacturer and user. The testsare shown in table 3.

7.1 Inspection practices

When inspection is specified,it may be carried outby

a number of alternative methods.

7.1.1 Inspection plans

It may be necessary to require inspection of certain

parameters of all hobs to be applied to a process.

However, quantities, available equipment, labor, and

inspection costs may influence the choice of using a

statistical sampling plan, such as provided byMIL--STD--105D.

7.1.2 Inspection data references

7.1.2.1 Reference axis

The reference axis of a hob is the guiding axis of the

hob (axis of the bore or the shanks). During

inspection, the hob must be mounted and held with

its reference axis in coincidence with the instrument

spindle axis.

7.1.2.2 Reference identification of tooth data

The hob shall be considered to be in top--coming

orientation, that is, with the reference axis horizontal

andthe sharpened flute faces in view at the top of the

hob (see figure 1). Then, the following terminology is

applied:

-- Flank (right or left). The surface bounding

the right or left side of a tooth when this tooth is

viewed with its tip above its root (top--coming).

-- Flank (lead or drag). The flank in which the

back--off or relief tends to increase the inclination

of thetooth flank surface from theplane of rotation

is the lead flank. This would be the right flank of ahob with a right hand thread lead and the left flank

of a hob with a left hand thread lead. The flank in

which the back--off or relief tends to decrease the

inclination of the tooth flank surface from the

plane of rotation is the drag flank. This would be

the right flank of a hob with a lefthand thread lead

and the left flank of a hob with a right hand thread

lead.

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7.1.2.3 Reference inspection zone

Where applicable, the tolerances apply to the

evaluation zone.

7.2 Bore diameter

The bore shall be checked for diameter and parallel-

ism. It shall also be checked for bearing area on an

accurate mandrel.

7.2.1 Bore diameter testing

The bore shall be checked for diameter and parallel-

ism. A mandrel of nominal size shall pass through

the bore as a check for alignment.

7.2.2 Bore diameter tolerances [Test No. 17]

Bore diameter tolerance is the maximum allowed

deviation on the bore of the hob. Tolerances are plus

(+) only.

7.3 Hub runout

7.3.1 Hub runout testing

The hob is rotated about its reference axis while hub

surface deviation is measured normal to the surface.

7.3.2 Hub runout tolerances

This standard provides tolerances for the following

hub runout parameters.

7.3.2.1 Hub face runout tolerances [Test No. 2]

Hub face runout tolerance is the maximum allowed

deviation on the end face of the hob.

7.3.2.2 Hub diameter runout tolerances

[Test No. 1]

Hub diameter runout tolerance is the maximum

allowed deviation on the hub diameter of the hob.

7.4 Outside diameter runout

7.4.1 Outside diameter runout testing

The hob is rotated about its reference axis while a

measurement probe is moved parallel to the refer-

ence axis in a linear, synchronized relationship

according to the thread lead. The probe is oriented

so that, as it is carried along the thread lead, the

probe tip will contact the passing tops of all teeth in

that lead, thus measuring their positions at the hob

outsidediametercutting edgein a direction normalto

the outside diameter cylinder.

7.4.2 Outside diameter runout tolerances [Test

No. 3]

Outside diameter runout tolerance is the maximum

allowed deviation between any two tooth tips.

7.5 Tooth face index

7.5.1 Tooth face index testing

The measurement probe is initially positioned to

contact the approximate center of a sharpened tooth

flute surface (tooth face) so as to measure normal to

the surface. Following the initial measurement, the

probe is retracted clear of the hob outside diameter

to permit repositioning to the next nominal tooth face

location. This repositioning involves rotation of thehob about its reference axis while the measurement

probe is moved parallel to the reference axis in a

linear, synchronized relationship according to the

thread lead.

This motion is carried out along the hob lead for an

incremental distance required to position the probe

at the nominal location of the next tooth face along

the thread. For straight flute hobs this increment is

based upon division of a circle according to the

number of hob flutes. For helical flute hobs thisincrement must also be adjusted according to the

flute lead. Once the incremental movement has

been completed, the probe is returned to the same

position on the tooth face and another measurement

taken. This repositioning of the probe from tooth

face to tooth face is repeated along the hob thread

until all flutes have been measured.

7.5.2 Tooth face index tolerances

This standard provides tolerances for the followingflute index parameters.

7.5.2.1 Tooth face index deviation, total

[Test No. 6]

Total flute index deviation is the maximum allowed

deviation between any two tooth face index

measurements.

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7.5.2.2 Toothface index deviation, adjacent [Test

No. 5]

Adjacent flute index deviation is the maximum

allowed deviation between any two consecutive

tooth face index measurements.

7.6 Flute lead

7.6.1 Flute lead testing

The measurement probe is moved parallel to the

reference axis, at the pitch diameter, for the full

cutting face width so as to follow the nominal path of

theflute. For hobs having helical flutes, the hob must

also be rotated about its reference axis in a linear,

synchronized relationship according to the flute

lead. As the probe follows the nominal path, it is

oriented to contact the sharpened tooth flute sur-

faces (tooth faces) as they pass by and measuretheir positions normal to the surface.

7.6.2 Flute lead tolerance [Test No. 7]

Flute lead tolerance is the maximum allowed devi-

ation as theprobe contacts thetoothfaces within any

100 millimeter axial region of the flute.

7.7 Rake offset to cutting depth

7.7.1 Rake offset testing

The measurement probe is positioned to contact the

sharpened tooth flute surface (tooth face) at the

depth of cut and midway between the left and right

flanks so as to measure normal to the surface.

Standard radial (zero rake) tooth face hobs require

positioning of the probe on center line for this test.

Hobs having offset tooth faces specified will require

positioning of the probe to a location offset from

centerline by the specified dimension. After the

probe is thus positioned at the appropriate starting

location, it is retracted along a path containing (forradial face) or parallel to (for offset face) the

centerline until the tooth outside diameter is passed.

7.7.2 Rake offset tolerance [Test No. 4]

The tolerance of rake to cutting depth is the

maximum allowed deviation as the probe traverses

the tooth face from whole depth to outside diameter.

7.8 Thread lead

Thread lead testing measures the displacement of

hob teeth along the thread lead. The tooth displace-

ments may be measured either at the actual cutting

edge or behind the cutting edge on the relieved tooth

flank. The default positionis over the cutting edge, at

the hob reference diameter as defined in clause 3.

7.8.1 Thread lead testing

7.8.1.1 Thread lead testing, over the edge

The measurement probe is moved parallel to the

reference axis, for the full cutting face width, while

the hob is rotated about the reference axis in a linear,

synchronized relationship according to the thread

lead. As the nominal lead is thus generated, the

probe is oriented to contact the passing tooth cutting

edges at the nominal pitch diameter, and measure

their displacements normal to the involute helicoid

surface approximated by the hob cutting edges.

Since measurements are taken at the cutting edge,

effects of variations in sharpening will be reflected in

the thread lead measurements.

7.8.1.2 Thread lead testing, on the flank

The measurement probe is initially positioned to

contacta relieved tooth flank behind the cutting edge

so as to measure normal to the involute helicoid

surface approximated by the hob cutting edges. The

first tooth selected for testingshould be at one end of

the cutting face width. Following the initial measure-

ment, the probe is retracted clear of the hob outside

diameter to permit repositioning to the next nominal

tooth flank location. This repositioning involves

rotation of the hob about its reference axis while the

measurement probe is moved parallel to the refer-

ence axis in a linear, synchronized relationship

according to the thread lead. This motion is carried

out along the lead for an incremental distance

required to position the probe at the nominal location

of the next tooth flank along the thread. For straight

flute hobs this increment is based upon division of a

circle according to the number of hob flutes. For

helical flute hobs this increment must also be

adjusted according to the flute lead. Once this

incremental movement has been completed, the

probe is returned to the same position on the next

tooth flank and another measurement taken. This

repositioning of the probe from tooth flank to tooth

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flank is repeated along the hob thread for the full

cutting face width. Since measurements are taken

on the tooth flank behind the cutting edge, effects of

variations in sharpening will not be reflected in the

thread lead measurement.

7.8.2 Thread lead tolerances

This standard provides tolerances for the followingthread lead parameters.

7.8.2.1 Lead deviation, in 3 axial pitches

[Test No. 12]

Lead deviation in 3 axial pitches is the maximum

allowed deviation between any two teeth contained

in 3 axial pitches.

7.8.2.2 Lead deviation, in 1 axial pitch

[Test No’s. 11 &11A]

Lead deviation in one axial pitch is the maximum

allowed deviation between any two teeth within any

group of consecutive teeth contained in one axial

pitch. The number of teeth in one axial pitch is that

number of teeth encountered by the measurement

probe as it moves parallel to the reference axis

during lead testing for a distance of one axial pitch of

the hob. This number of teeth will be determined by

the number of flutes, the number of threads, and, in

the case of helical flute hobs, the flute lead.

7.8.2.3 Lead deviation, adjacent tooth--to --tooth

[Test No. 10]

Adjacent tooth--to--tooth lead deviation is the

maximum allowed deviation between any two

consecutive teeth.

7.9 Thread spacing

7.9.1 Thread spacing testing

The measurement of thread spacing of multiple

thread hobs may be carried out by either of twomethods depending upon whether hob evaluation is

to be carried out by elemental or composite

methods. See 5.5.1.

When elemental method evaluation is selected,

thread spacing testing is based upon thread lead

testing of the given flank at appropriate angular

increments. The position of each thread is deter-

mined by the thread lead testing procedure de-

scribedin 7.8. Afterthe first thread is thus measured,

the hob must be repositioned to the nominal of the

next thread. For lead testing over--the--edge proce-

dures, this repositioning is based upon division of a

circle according to the number of threads. For lead

testing on--the--flank procedures, the repositioning

will require additional adjustment in hob and mea-surement probe location according to the number of

flutes, thread lead, and in the case of helical flute

hobs, flute lead. Once this incremental repositioning

has been completed, the probe is returned to the

testing diameter and the thread lead testing is

resumed. Thread lead testing and incremental

repositioning is repeated until the position of each

thread has been measured.

When composite method evaluation is selected,

thread spacing testing is based upon line of actiontesting of the given flank at appropriate angular

increments. The position of each thread is deter-

mined by the line of action testing procedure

described in 7.12.1.1. After the first thread is thus

measured, the hob must be repositioned to the

nominal location of the next thread. This reposition-

ing is based upon divisionof a circle accordingto the

number of threads. Once this incremental reposi-

tioning has been completed, the probe is returned to

the testing diameter and thread lead testing is

resumed. Line of action testing and incrementalrepositioning is repeated until the position of each

thread has been measured.

7.9.2 Thread spacing tolerance

This standard provides tolerances of the following

thread spacing parameters.

7.9.2.1 Thread spacing tolerance, total

When elemental method evaluation is used (Test

16), total thread spacing tolerance is the maximum

allowed deviation between the average values of

lead measurements on the given flank of any two

threads along the length of the hob. When compos-

ite method evaluation is used (Test16A), total thread

spacing tolerance is the maximum observed devi-

ation between the average values of line of action

measurementson thegiven flank of any twothreads.

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7.9.2.2 Thread spacing tolerance, adjacent

When elemental method evaluation is used (Test

15), adjacent thread spacing tolerance is the maxi-

mum allowed deviation between the average values

of lead measurements on the given flank of any two

adjacent threads along the length of the hob. When

composite method evaluation is used (Test 15A),

adjacent thread spacing tolerance is the maximum

observed deviation between the average values of

lineof action measurementson thegiven flank of any

two adjacent threads.

7.10 Tooth profile

7.10.1 Tooth profile testing

Hob tooth profile testing may be carried out accord-

ing to a variety of procedures as described in the

following paragraphs. The default is “on--the--flank”

for test 8 and “over--the--edge” for test 8A.

7.10.1.1 Tooth profile testing, over--the--edge

Tooth profile testing over--the--edge involves mea-

surement of tooth cutting edge profile displacement

at a series of incremental positions from root to tip of

the hob tooth relative to the incremental positioning

of themeasurement probe along thespecified angle.

At each of the incremental test positions, the probe is

moved across the cutting edge in a helical lead

movement as described in 7.8.1.1. After the probe

has passed the cutting edge and measured the

displacement, the helical lead motion is reversed

until hob andprobe returnto the starting position with

the probe just behind the cutting edge. During the

reverse motion, the probe may be temporarily

retracted so that it does not catch on the sharp

cutting edge. Following the reverse motion, the

probe is moved to the next incremental location

along the specified angle. The helical lead motion

can then be repeated at the new profile location.

This incremental repositioning of the probe accom-

panied by individual helical lead movements across

successive tooth cutting edge profile locations

continues until the full profile has been traversed.

The probe must be oriented so that contact with the

cutting edge occurs only within the specified plane

and so as to measure cutting edge displacement

normal to the involute helicoidsurface approximated

by the hob cutting edges.

7.10.1.2 Tooth profile testing, on--the--flank

Tooth profile testing on --the--flank involves move-

ment of the measurement probe from the root to the

tip of the hob tooth at the specified angle while in

contact with the tooth flank behind the cutting edge.

The probe must be oriented so that contact with the

flankoccurs only within the specified plane and so as

to measure flank displacement normalto theinvolute

helicoid surface approximated by the hob cutting

edges.

7.10.1.3 Tooth profile testing, axial

Axial tooth profile testing assumes that the helical

hob thread should contain a straight profile at the

intersection of the thread and an axial plane. Testing

may take place either on--the--flank or over--the--

edge. The specified angle is theaxial pressure angle

and the specified plane is the axial plane.

7.10.1.4 Tooth profile testing, normal

Normal tooth profile testing assumes that the helical

hob thread should contain a straight profile at the

intersection of the thread and a normal plane.

Testing may take place either on--the--flank or

over--the--edge. The specified angle is the normal

pressure angle andthe specified plane is the normal

plane.

Normal tooth profile testing may also be accom-

plished by projection. A shadow of the tooth may be

optically magnified to permit comparison of the

profile to a large scale layout of the specified profile.

This method requires orientation of the hob tooth

with the optical projection system.

7.10.1.5 Tooth profile testing, involute helicoid

generator

Involute helicoid generator tooth profile testing

assumes that the helical hob thread should contain a

straight profile at the intersection of the thread and

plane of action. The plane of action is a plane

tangent to the base cylinder of the hob. This

geometry system assumes that hob geometry, at the

cutting edges,is the sameas that ofa helical involute

gear. Hobs conforming to this geometry system will

generate true involute profiles on gears cut. Hobs

conforming to axial or normal profile geometry

systems will produce some tip and root relief relative

to a true involute on the gears cut. See Annex C.

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Testing may take place only over--the--edge. The

specified angle is the hob lead angle at the base

diameter and the specified plane is the plane of

action.

7.10.2 Tooth profile tolerances [Test No’s 8 & 8A]

This standard provides tolerances that are applica-

ble only to measurements of involute helicoid tooth

profile for those cases where the hob has been

specified to be manufactured with that tooth geome-

try. The tooth profile tolerance is the maximum

allowed deviation as the probe traverses the speci-

fied angle from whole depth to edge round at the

outside diameter, exclusive of any specified modifi-

cations deviating from the straight profile.

7.11 Tooth thickness

7.11.1 Tooth thickness testing

The measurement probe is oriented to contact the

cutting edge and measure the displacement normal

to the hob thread helix at the reference diameter and

tangent to the cylinder of the reference diameter. If

the hob is non--topping, the reference diameter is the

outside diameter minus (2) hob addendums. If the

hob is topping, the reference diameter is the root

diameter plus(2) hobdedendums. Theprobe is then

relocated to a comparable location in contact with

the opposite tooth flank. Differences in probe

position and cutting edge displacement measure-

ments will determine actual tooth thickness in the

normal plane.

Tooth thickness may alternatively be tested by

projection. A shadow of the tooth may be optically

magnified to permit comparison to a large scale

specified layout. The tooth thickness should be

observed at thereference diameter of thetooth. This

method requires orientation of the hob tooth with the

optical projection system, and will determine actualtooth thickness in the normal plane.

7.11.2 Tooth thickness tolerance [Test No. 9]

Tooth thickness tolerance is the maximum allowed

deviation between any measured tooth thickness

and specified tooth thickness. The tolerance is

minus (--) only.

7.12 Line of action

Line of action testing permits an observation of how

all the elements of hob geometry come together to

generate an involute gear profile. While this

composite type of testing procedure is of limited

value to process control of hobs,it can be a valuable

tool indetermininghow well a given hob may workfor

its intended purpose.

As two mating gear teeth pass through mesh, they

contact one another at constantly changing diame-

ters as the point of contact moves along the line of

action tangent to both their base circles. The

engagement between a gear tooth and its generat-

ing hob occurs along a similar line of action.

Successive teeth along the thread lead encounter

the gear profile at constantly changing diameters.

Each encounter of the gear profile with a hob tooth

cutting edge occurs along the line of action.

Ordinarily, the two most significant elements of hob

geometry are lead and profile. Line of action testing

permits an observation of the combined effect of the

deviations of these two important parameters. Since

line of action testing theory assumes that a hob

should represent involute helicoid geometry just like

a gear, the test is performed in the plane of action of

the hob tangent to its base cylinder. Thus, the line of

action test will reveal the effect of the gear profile tip

and root relief resulting from allowed normal or axial

hob profiles. Since the test is carried out across the

cutting edge, the effects of sharpening deviations

are also included in this composite test.

7.12.1 Line of action testing

Hob line of action testing may be accomplished

either by direct measurement or by modeling based

on lead and involute helicoid generator profile test

data. Testing will occur over the unmodified portion

of the hob tooth.

7.12.1.1 Line of action testing, direct

measurement

Line of action testing of a hob involves moving the

measurement probe along the thread line of action

so as to permit measurement of cutting edge

displacements from their proper positions. This

complex motion may be considered as a combina-

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tion of two basic components. First is the rotation of

the hob about its reference axis while the measure-

ment probe is moved parallel to the reference axis,

so as to generate the nominal lead of the thread. As

this occurs, the motion of the probe is modified so

that it will contact each successive tooth along the

thread at a constantly increasing (or decreasing)

diameter. Actually, the probe is caused to movealong the profile in a manner described under

involute helicoid generator profile testing (see

7.10.1.5) while simultaneously progressing along

the thread lead. As the nominal line of action is thus

generated, the probe is oriented to contact the

passing tooth cutting edges and measure their

displacements normal to the involute helicoid sur-

face approximated by the hob cutting edges. Since

interaction of the various elements of hob accuracy

typically varies at different locations around a hob, it

is recommended that line of action testing be carriedout at multiple locations. It is alsorequired that lineof

action measurements be observed on both flanks of

all threads.

7.12.1.2 Line of action testing, modeled from

lead and profile data

Thread lead and involute helicoid generator profile

test data can be combined in such a manner as to

provide equivalent data as would be derived from a

direct line of action measurement. The thread lead

data for a given flankof a selected thread is collected

as described in 7.8.1.1, thread lead testing over--

the--edge. Profile data for the same flank and thread

is collected as described in 7.10.1.5, tooth profile

testing, involute helicoid generator. Since this profile

test must take place over the cutting edge, refer also

to 7.10.1.1. Additionally, the incremental positions

selected along the profile must correspond to those

locations which would be encountered during a

direct measurement of line of action.

Only one thread lead test data set and one involute

helicoid generator profile test data set taken on the

same flanks of the same hob thread can be

combined to produce a modeled line of action test

data set. Once this data is collected, it must be

combined by the summation of successive lead and

profile test data samples to create successive line of

action model data samples. The lead and profile

data summation procedure must be organized with

regard to the order of data combination (i.e., profile

root to tip or tip to root, lead start to end or end to

start) so as to create a valid line of action model.

In the case of a hob designed with minimum cutting

face width required to generate a full gear profile, the

number of lead and profile data samples will be

approximately equal. For hobs with greater cutting

face widths, the additional lead data samples will

permit the creation of multiple line of action models

by the combination of profile data with multiple

groups of lead data. This is recommended since

interaction of the various elements of hob accuracy

typically varies at different locations around a hob. It

is also required that line of action be observed on

both flanks of all threads.

7.12.2 Line of action tolerances

The hob line of action tolerances provided by this

standard may be applied to line of action tests for

those cases where the hob has been specified to be

manufactured with involute helicoid geometry. Hob

line of action tolerances may be thus applied to the

following line of action parameters.

7.12.2.1 Line of action deviation, total[Test No. 14]

Total line of action deviation is the maximum allowed

deviation between any two teeth of a given line of

action test. Total hob line of action tolerances may

be applied to total line of action test results for those

cases where the hob has been specified to be

manufactured with involute helicoid geometry.

7.12.2.2 Line of action deviation, adjacent

[Test No. 13]

Adjacent line of action deviation is the maximum

allowed deviation between any two consecutive

teeth of a given line of action test. Adjacent hob line

of action tolerances may be applied to adjacent line

of action test results for those cases where the hob

has been specified to be manufactured with involute

helicoid geometry.

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