11. A double helical gear can be thought of as two mirrored helical gears joined together. 12. Two main turbines were arranged in series and drove a shaft through double helical gears . 13. Previously, gears had been helical gears . 14. The term crossed helical gears has superseded the term " spiral gears ". 15. However, double helical gears are more difficult to manufacture due to their more complicated shape. 16. To machine a helical gear on a manual machine, a true indexing fixture must be used. 17. It applies to spur gears, parallel axis or crossed axis helical gears , and worm gearing. 18. The transmission included helical gear drive, a wet clutch, and a three-speed gearbox. 19. Helical gears connect parallel shifts but the involute teeth are cut at an angle to the axis of rotation.20. Amongst South African electric locomotives, the Class 14E was the first to have solid wheels with helical gears .
