Rolls-Royce Archives
         « Prev  Box Series  Next »        

From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Diagrams and tables detailing involute gear design, hobbing, and manufacturing limits.

Identifier  ExFiles\Box 136\5\  scan0344
Date  15th January 1940 guessed
  
COMMON TERMS IN INVOLUTE GEAR DESIGN
Fig. #1
Diagram labels: Pitch Point, Base Circle, Pitch Line, PA{Mr Paterson}, Common Tangent, Driver, Angle Of Recess, Arc Of Action With Approach, Full Arc Of Action Without Approach, Minimum Arc Of Action, Angle Of Approach, Desired Approach, Minimum Addendum For Continuous Action.

Limits for Single and Multiple Thread Ground Finishing (Spur and Spiral) Gear Hobs
Fig. #2
DIAMETRAL PITCH | 1 to 1 3/4 | 2 to 2 3/4 | 3 | 4 | 5 | 6 to 12 | 13 to 50
--- | --- | --- | --- | --- | --- | --- | ---
HOLE DIAMETER | Must be lapped straight, parallel, not less than 75% bearing length.
Hole within (plus only) | A .0008 B .001 | A .0005 B .0007 | A .0003 B .0005 | A .0002 B .0003 | A .0002 B .0003 | A .0002 | A .0002
| | | | | | B .00025 | B .00025
HUB RUN-OUT
Face within | A .0008 B .001 | A .0005 B .0007 | A .0003 B .0005 | A .0002 B .0003 | A .0002 B .0003 | A .0002 | A .0002
| | | | | | B .00025 | B .00025
Diameter within | A .001 B .0012 | A .0007 B .0008 | A .0005 B .0006 | A .0003 B .0005 | A .0003 B .0005 | A .00025 | A .00025
O.D. Run-Out
Up to 3" Diameter | A .001 B .001
3 to 4" Inclusive | A .0015 B .0015 | A .001 B .001
Over 4" Diameter | A .003 B .004 | A .002 B .003 | A .0015 B .0015 | A .001 B .001
Spacing from Flute to Flute within | A .002 B .005 | A .002 B .005 | A .0015 B .003 | A .001 B .003 | A .001 B .001 | A .001 B .001
Accumulated error in one revolution must not exceed | A .010 B .012 | A .009 B .010 | A .007 B .009 | A .005 B .008 | A .003 B .005 | A .003 B .004
CUTTING FACES
Must be radial within (Cutting Depth) | A .003 B .005 | A .0015 B .0025 | A .001 B .0015 | A .001 B .0008 | A .0007
THREAD
Lead variation in any one complete turn must not exceed | A .0025 B .0035 | A .001 B .0025 | A .0006 B .0015 | A .0005 B .0013 | A .0005 B .0010 | A .0004 B .0006
Lead variation from tooth to tooth must not exceed | A .0007 B .001 | A .0005 B .0008 | A .0004 B .0007 | A .0003 B .0005 | A .0002 B .0004 | A .0002 B .0003
TOOTH PROFILE OR PRESSURE ANGLE
Must be symmetrical within | A .001 B .0015 | A .0007 B .001 | A .0005 B .0006 | A .0004 B .0005 | A .0003 B .0004 | A .0002 B .0003 | A .0002 B .0002
Straight portion within | A .001 B .0016 | A .0005 B .0008 | A .0004 B .0005 | A .0003 B .0004 | A .0002 B .0003 | A .0002 B .0002
Start of approach within plus or minus | A .020 B .022 | A .018 B .020 | A .015 B .015 | A .010 B .010 | A .008 B .006 | A .005 B .005
Approach on each side of tooth symmetrical within | A .015 B .018 | A .012 B .015 | A .010 B .010 | A .008 B .006 | A .006 B .005 | A .005 B .005
Tooth thickness within minus only | A .003 B .003 | A .002 B .002 | A .002 B .002 | A .002 B .002 | A .001 B .001 | A .001 B .001
MULTIPLE THREADS
Circular Pitch Within | A .005 B .005 | A .003 B .003 | A .0020 B .0020 | A .0015 B .0015 | A .0010 B .0010 | A .0007 B .0007 | A .0005 B .0005
The classification of a hob is determined by the finest limit of any one feature. Chart No. 3

Fig. #3
Hob with relief-ground teeth
Labels: Machine-relieved portion, Relief-ground portion.

Fig. #4
Labels: HOB, GEAR BLANK.
Caption: THE INVOLUTE IS GENERATED BY SUCCESSIVE CONTACT OF A NUMBER OF HOB TEETH IN THE GENERATING PLANE.
Side label: GEAR TOOTH AS GENERATED BY HOB.
  
  


Copyright Sustain 2025, All Rights Reserved.    whatever is rightly done, however humble, is noble
An unhandled error has occurred. Reload 🗙