| Type |
Precision
Rating |
Features |
Application |
Comments Precision |
| Spur |
Excellent |
Parallel shafting. High speeds and loads. Highest efficiency. |
Applicable to all types of trains and a wide range of velocity ratios. |
Simplest tooth elements offering maximum precision. First choice, recommended for all gear
meshes except where high speeds and loads or special features of other types, such as right-angle drives cannot be avoided. |
| Helical |
Good |
Parallel shafting. Very high
speeds and loads. Efficiency slightly less than spur mesh. |
Most applicable to high speeds
and loads; also used wherever spurs are used. |
Equivalent quality to spurs except for
complication of their angle. Recommended for all high-speed and high-load meshes. Axial thrust component must be accommodated. |
| Crossed-Helical |
Poor |
Skewed shafting, point contact, high sliding, low speeds and light loads. |
Relatively low velocity ratio; low speeds and light loads only. Any angle skews shafts. |
To be avoided for precision meshes. Point contact limited capacity and precision.
Suitable for right-angle drives if light load. A less expensive substitute for bevel gears. Good lubrication essential because of point contact and high sliding action. |
| Internal Spur |
Fair |
Parallel shafts, high speeds, high loads. |
Internal drives requiring high speeds and high loads;
offers low sliding and high stress loading; good for high capacity long life. Used on planetary gears to produce large reduction ratios. |
Not recommended for precision meshes because of design,
fabrication and inspection limitations. Should only be used when internal feature is necessary. |
| Bevel |
Fair to good |
Intersecting shafts, high speeds, high loads. |
Suitable for 1:1 and higher velocity ratios and for right-angle meshes (and other
angles). |
Good choice for right-angle drive particularly low ratios. However, complicated tooth
form and fabrication limits achievement or precision. Should be located at one of the less critical meshes of the train. |
| Worm Mesh |
Fair to good |
Right-angle skew shafts, high velocity ratio, high
speeds and loads. Low efficiency, most designs nonreversible. |
High velocity ratio, angular meshes, high loads. |
Worm can be made to high precision, but worm gear has
inherent limitations. To be considered for average precision meshes, but can of high precision with care. Best choice for combination high velocity ration and
right-angle drive. High sliding requires excellent lubrication. |
