The Concurve generating tool is designed such that it will not "undercut," even when machining gears with very low numbers of teeth, down to as few as four.
Again, in contrast, one of the largest restraints in designing Involute gearing is the limitation on the minimum number of teeth due to the tendency of the generating tool to undercut or generate away the tooth profile in the region below the base circle. This obviously decreases the tooth bending strength considerably.
For example, AGMA recommends a minimum of 18 teeth for standard Involute forms of 20-degree pressure angle.
Apart from these improvements, Concurve gearing has retained all the advantages of standard gearing such as:
- Simplicity of conventional cutting tools. The Concurve generating tool with its curved profile is easily produced with present day toolmaking techniques.
- Relative insensitivity to errors in mounting center distance. Conjugate action remains essentially correct with normal variations in center distance.
- Production on conventional machines and in conventional ways such as hobbing, grinding, shaping and powder metal or plastic molding.
Because of these improvements, the Concurve gearing development has removed many of the constraints that have long been troublesome to gear designers. In design situations where low numbers of teeth (on one or both members of a gear set) would be desirable, Concurve gearing now offers the best solution.
Summarizing - the major inherent features in Concurve gearing are:
- Lower contact stress in the critical area below the pinion pitch line (due to constant relative tooth curvature).
- Lower tooth bending stress as a result of no undercut.
- Fewer gear teeth. Even a pair of 5-tooth pinions is possible.
These basic benefits can become physical and economic advantages such as:
- Higher torque/horsepower capacity from the same size gear set
- Higher ratios in a single gear set, 20:1 and higher
- Size and weight reduction due to fewer and smaller parts
- Increased wear and scoring resistance which results in increased life
- Higher reliability as a result of fewer parts and higher capacity