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8/15/2019 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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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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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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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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ANSI/AGMA 1102--A03AMERICAN NATIONAL STANDARD
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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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¢
[Multiiple Thread Sum]
Test 15, 15A: Threadspacing adjacent = 1/ 3¢0.7¢
[Multiiple Thread Sum]
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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