Spur Gears

Spur gears are straight-toothed gears with radial teeth that transmit power and motion between parallel axes. They are widely used for speed reduction or increase, torque multiplication, resolution, and accuracy enhancement for positioning systems. Gear types available for spur gears and straight tooth gears, metric include spur or pinion gears, change gears, cluster gears, internal gears, differential end gears, and racks. Straight tooth gears contain teeth that run parallel to the axis of the gear. Racks and pinions, and spur, internal, and cluster gears are included in this grouping. Metric gears have a millimeter-based module designation. Other gears may have curved or helical tooth paths or teeth on a conical surface, and are covered on other search forms.

Gears mate or mesh via teeth with very specific geometry.  It is important to consider pitch when searching for spur gears.  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. Gears must have the same pitch and pressure angle in order to mesh. Other important specifications to consider include the gear center, bore diameter, and shaft diameter.  The gear center can be a center bore or an integral shaft.  The bore diameter is the diameter of center bore for spur gears with a bore.  The shaft diameter is the diameter of shaft for gears with integral shaft.

Materials of construction for spur 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, nylon, and polycarbonate.  Ground teeth provide smoother, higher-precision tooth form.  Combination gears can have plastic teeth with metal inserts.  Spur gears 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 spur 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.

• Strength Of Plastic Spur Gears
  In the following text, main consideration will be given to Nylon MC901 and Duracon M90, However, the basic equations used are applicable to all other plastic materials if the appropriate values for...
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• Fundamentals of Helical Gears
  In Figure 5-2 the gear train has a difference of numbers of teeth of only 1; z1 = 30 and z2 = 31. This results in a reduction ratio of 1/30. SECTION 6 HELICAL GEARS The helical gear differs from the...
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• Manual of Gear Design: Spur and Internal Gears, Volume II
  Manual of Gear Design: Spur and Internal Gears, Volume II Offering many solutions of general spur and internal gear problems, this volume contains plane trigonometry formulas and examples, and...
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Part Numbers for Spur Gears