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.
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.
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.
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.
What’s the difference between Helicon and Spiroid?
The differences between Helicon and Spiroid gear forms are all attributable to geometry. As the images to the right illustrate, Helicon pinions are cylindrical and engage a flat-faced gear. Spiroid pinions, on the other hand, have a conical shape and engage a bevel-faced gear. What does this mean for your application?
Backlash Adjustment: Helicon gear sets allow for axial shimming of the face gear to achieve backlash adjustability. Conversely, Spiroid’s gear set geometry allows for axial shimming of both the face gear and pinion. Said another way, the Spiroid gear form offers finer backlash control.
Efficiency & Torque: All else being equal, efficiency and torque act as minor tradeoffs when comparing Spiroid and Helicon gear set performance. Relative to one another, Helicon gear sets gain efficiency at the expense of torque while Spiroid gear sets gain torque at the expense of efficiency. It should be noted that these differences are often negligible and can only be properly assessed within the context of a specific application.
Complexity: Spiroid’s gear form geometry introduces unique challenges to hob design, hob manufacturing, and overall gearset development. All of this has the potential to impact overall costs. In the right applications, these costs can be easily outweighed by Spiroid’s unique advantages.
Conclusion: Throughout our 50+ year history we’ve found that very few applications hinge upon the differences between Helicon & Spiroid. As a result, Helicon is commonly preferred over Spiriod, except in select applications requiring a need for finite backlash control and higher torques. At the end of the day, we’ve learned that it is best practice to narrow your search based on desired gear OD, ratio, required torque and/or other parameters relevant to your application.