Worms and Worm Gears

Worm gears are cylindrical gears with a spiral thread that drive mating worm wheels in high-reduction gearset applications. They operate on non-intersecting perpendicular axes.  Worm gears are widely used for speed reduction or increase, torque multiplication and resolution, and accuracy enhancement for positioning systems. Worm gear drives provide substantial speed reduction and torque multiplication in a comparatively small design package. 

Worm gears mate or mesh via teeth with very specific geometry.  Pitch is a measure of tooth spacing and is expressed in several ways: Circular pitch (CP) is a direct measurement of the distance from one tooth center to the adjacent tooth center. Diametral pitch (DP) is the ratio of number of teeth to the pitch diameter (in inches) of a gear; a higher DP therefore indicates finer tooth spacing. This is the most common pitch designation for gears with English design units.  Module (mod or M) is used for metric gears and is the ratio of pitch diameter (in mm) to the number of teeth; a higher module therefore indicates coarser tooth spacing.  Pressure angle is another specification of tooth form and is the angle of tooth drive action, i.e. the angle between the line of force between meshing teeth and the tangent to the pitch circle at the point of mesh. Worm gears must have the same pitch and pressure angle in order to mesh.  Other important parameters to consider include number of teeth, face width, and gear hand direction.  Worm gears have a right or left hand specification, which describes the direction of tooth curve. 

Materials of construction for worm wheel gears can be metal or plastic. Gears are made from a wide variety of materials with many different properties. Factors such as design life, power transmission requirements, noise and heat generation, and presence of corrosive elements contribute to optimization of gear material. Consult with a gear manufacturer on a specific application for the best material.  Metal choices include aluminum, brass, bronze, cast iron, steel, hardened steel, and stainless steel.  Plastic choices include acetal, Delrin, nylon, and polycarbonate.  Ground teeth provide smoother, higher-precision tooth form.  Combination gears can have plastic teeth with metal inserts.  Worm gears, metric can be mounted on a hub or shaft.  A hub is a cylindrical projection on one or both sides of gear, often for the provision of a screw or other shaft attachment mechanism. Hubless gears are typically attached via press fit, adhesive, or internal keyway.  Shaft mounting choices include keyway, set screws, hub claming screws, split, and simple bore.

• Worm Gears
  Worm gears are right angle devices providing large speed ratios on a comparatively short center distance. Worm and worm gears operate on non-intersecting shafts at 90 degree angles....
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• Strength Of Worm Gearing
  This information is applicable for worm gear drives that are used to transmit power in general industrial machines with the following parameters....
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• Details of Involute Gearing
  1. Face Gear This is a pseudobevel gear that is limited to 900 intersecting axes. The face gear is a circular disc with a ring of teeth cut in its side face; hence the name face gear. Tooth elements...
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