11 Worm Gear Assembly, Tolerances, and Inspection

These three requirements for acceptable worm gearing performance are effected by a wide range of unclear specifications. The only criteria is to have satisfactory operation for a stated time period. When gears run smoothly, without vibration, carry the rated load for the required number of hours without breakage or problematic wear at reasonable temperatures, and operate quietly, we have succeeded.

When worms are difficult to assemble to the mating wheel or, for whatever reasons, are unsatisfactory and if accuracy, high speeds, or large powers are required, then systematic methods of inspection are essential. This inspection must be combined with the necessary requirement of having manufactured the gear drive correctly, within the specified tolerances. The only reason for tolerances is to consistently produce gears to the required quality level so they operate correctly with the mating gear. Tolerances that are closer than necessary will increase cost and tolerances must, therefore, be applicable to the demands that will be placed upon the gearing.

Worm gearing, while similar in respect to other forms of gearing, have their own idiosyncrasies when the tolerances, inspection, and assembly are planned. An added complication is the wide range of worm gear applications. Each application has its' own special requirement. The situation may require one or more of the following: minimum backlash, high speed, accurate positioning or indexing, long life, short life, and high strength. Inspection of the worm, then the worm wheel and, afterwards, the pair together is a requirement for both precision and high speed. As a result of knowing what to do speeds are now being achieved beyond what anyone contemplated in the past.