The Gear tool options palette.
This tool may be executed in two different ways: With a single click, when Preset is checked, or with two or three dynamically entered clicks, when Dynamic is checked. These and other options are selected from its Tool Options palette.
Model Type: Either Facetted or Smooth gears can be generated.
Type: Gears can be either Surface or Solid objects.
When the Creation Method is Preset, additional parameters need to be set. Width is only used when Solid is selected and represents the distance between the two flat faces of the gear. Number Of Teeth is the tooth count and is used in determining the outer diameter of the gear and the gear ratio of any final gear train. Outer Diameter is a non-editable information field that displays the size of the outer diameter, which is calculated from the number of teeth and the diametral pitch.
When Dynamic is used, the gear is generated through two or three mouse clicks, depending on whether it is a surface or solid object, respectively. The first click sets the center of the base. The second click establishes the diameter (size) of the gear. If it is a solid gear, the third click sets the width (extrusion distance) of the gear.
The remaining options, at the lower end of the Gear Tool Options palette, determine the shape of the teeth of the gear.
Diametral Pitch: This is the ratio between the number of teeth and a unit diameter distance and determines the number of teeth a gear has for a unit of diameter. For example, a diametral pitch of 20 teeth/inch means that a gear with 20 teeth will have a diameter of one inch, measured at the effective point of contact. A larger pitch value will result in a gear with more teeth for a given diameter. Consequently, the diameter of the pitch circle (d) is the product of the diametral pitch (pd) and the number of teeth (N): d = (pd)(N). If all other parameters are unchanged, a larger pitch results in a smaller outer diameter.
Pressure Angle: This parameter determines the ‘steepness’ of the gear teeth. Smaller values will produce thinner gears that have less drag but are also weaker. 14.5º and 20º are common standard values. Note that gears that are intended to mesh should have identical values for both the Pressure Angle and Diametral Pitch. See examples below.
Gear teeth with pressure angle at (a) 20°, (b) 14.5° and 26°, and (c) 14.5°.
Base Fillet Radius: This value is used to create a fillet at the bottom corners of the land between teeth. It is ignored if there is insufficient clearance between teeth for the requested value. Generally, large numbers of teeth or large pressure angles will create crowding and require smaller base fillet radius values.
Center Bore Radius: This option will create a central hole in the gear blank. It will be ignored if a value is given that is larger than the outer diameter of the gear.
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