A standardization of the gears (module, pressure angle and profile) is required to guarantee the gears when replacing, which are made by different manufacturers, and to limit the number of different tools. Through this the attention of the designers is also drawn to use a certain standardization in the choice of the form and the ratio of the gears.
The first requirement for a good gear is that this must have been manufactured economically. A gear with wrong ratio’s or of a complicated design is always more expensive than a gear that corresponds to the classic design.
For standard gears there is a tendency to standardization of certain proportions that we highlight below. The larger variety of transmissions for which everchanging conditions of “available space”, speed, stability, power, location of the axes etc. occur excludes a general standardization of the design. There is often “a most rational” solution for each case. In order to help the “designers”, we have included in a table of the standard forms, the most common types.
Standard pinions, with or without extended hub (form 1. 2.3.)
- Facewidth = 10 x the module in mm
- Bore = normal diameter and keyway (see below in the tables)
Standerd wheels, with cross spokes, symmetrical or extended hub, manufactured of cast steel, cast iron or welded construction (Form 6. 7.13.)
- Rim width = 10 x the module in mm
- Bore = normal diameter and normal keyway
- Nave diameter = 2 x diameter of the bore
- Thickness under the tooth: minimum 1.5 x the module for steel, minimum 2 x the module for cast iron
- Number of spokes = 4, 5 or 6 depending on the diameter of the wheel
Bevel gears, (Form 20 to 25).
- Facewidth = maximum 1/3 of the outer cone distance
- For bore and nave = see straight gears
Worm and worm wheels (form 16 to 19)
- The pitch circle diameter of the worm is generally chosen in accordance with the existing pitch circle diameter of an existing reference hob and in function of the desired efficiency.
- The worm length depends mainly on the pitch circle diameter of the gripping worm wheel usually = 2 x the pitch circle diameter of the worm.
- The width of the rim: < pitch circle diameter of the worm wheel.