BS 978-5:1965

Co-operating organizations
Foreword
Specification
Section 1. Hobs for fine pitch gears
1.1 Scope
1.2 Terminology
1.3 Tooth form
1.4 Gashes
1.5 Bores
1.6 Dimensions
1.7 Tolerances
1.8 Marking
1.9 Purchasing recommendations
Section 2. Rotary form-relieved gear cutters for fine
           pitch gears
2.1 Scope
2.2 Terminology
2.3 Tooth form
2.4 Cutter groups
2.5 Dimensions
2.6 Tolerances
2.7 Circumferential form relief
2.8 Arbor tolerances
2.9 Marking
2.10 Purchasing recommendation
Section 3. Pinion type cutters for fine pitch gears
3.1 Scope
3.2 Terminology
3.3 Tooth form
3.4 Dimensions
3.5 Cutting rake
3.6 Bore
3.7 Provision of datum cylinder
3.8 Tolerances
3.9 Marking
3.10 Purchasing recommendations
Appendices
A Marking code for cutters for fine pitch gears
B Basic rack tooth profiles (B.S. 978, Part 1)
C Basic rack tooth profile (gear and cutter) B.S.
      978, Part 2 addendum No. 1
Tables
1 General dimensions of hobs
2 Tolerances
3 General dimensions of rotary form-relieved cutters
4 Unit pitch dimensions of cutter profiles for
      involute teeth to Figs. 1 and 2 of B.S. 978, Part
      1
5 Tolerances
6 Disc type gear cutter dimensions
7 Extended hub gear cutter dimensions
8 Screwed hub gear cutter dimensions
9 Parallel shank gear cutter dimensions
10 Taper shank gear cutter dimensions
11 Tolerances

Applies to single-start, topping and non-topping, right and left-hand hobs for production of spur and helical gears in the pitch ranges 24 D.P. to 200 D.P. and 1 mm to 0.127 mm module inclusive. Three grades of hobs are covered, viz. Grade A for production of precision gears, Grade B for gears for high class work and Grade C for general engineering.