Design

Gear Handedness

A Helicon or Spiroid gear set is either left or right hand. The “Hand” is determined by the direction of the pinion thread (clockwise/counter clockwise).  The two images below illustrate relative pinion positions for both left and right hand systems, enabling design flexibility.  

Left Handed Helicon

Left Handed Gearing

Right Handed Helicon

Right Hand Gear

High Side / Low Side Pressure Angles

As the figure below demonstrates, Helicon and Spiroid tooth pressure angles are not symmetrical. However, Helicon and Spiroid gearing operate at approximately the same efficiency and load rating in either direction of pinion rotation. This, despite the fact that direction and magnitude of the forces on the teeth are different.

These forces tend to separate the pinion and gear teeth. They are largely in the axial direction of the pinion but there are also force components working in the radial direction of the pinion. With respect to the pinion, this radial component is greater when the driving is done on the high-pressure-angle side of the tooth.

Generally, due to bearing life considerations - and to extract the most from Spiroid's gearing technology - it is preferable in single-direction drives to do the driving on the low-pressure-angle side of the pinion thread. 

See description of this within ‘Tooth Load Components’ under ‘Process Deliverables’.

 

Materials Selection

Spiroid's contact line movement, lower sliding condition and ideal lubricating film formation permit the use of hardened steel material for both gears and pinions. This is particularly advantageous in situations where high surface durability, high static loads, running loads or shock loads are encountered.

As shown in the table below, theoretical performance ratings for Spiroid and Helicon may be de-rated depending upon the materials selected. Spiroid always recommends validation through testing as the best way to fully confirm performance ratings.

Service Factors

Horsepower and torque ratings are based on a unity service factor (1.0) as defined in the table below. The ratings given in the tables are surface durability capacities and do not take into account any thermal limits.

 

Helicon & Spiroid Comparison: Design

For a comprehensive review of the differences between Spiroid and Helicon, see our ‘Helicon & Spiroid Comparison’ pdf linked below.

Helicon and Spiroid Comparison PDF