WORMS GEARS: ROTATION AND RATIO
Figure 4.10 indicates the various directions worms and worm gears will rotate depending on their position and hand.
• Changing the position of the worm (above or below the worm gear) changes the relative rotation of the worm gear.
• The direction of rotation using right-hand gearing is shown at the top.
• The direction of rotation using left-hand gearing is shown at the bottom.
The ratio of a mating worm and worm gear is determined by dividing the number of teeth in the worm gear by the number of threads in the worm or:
Ratio = Number of teeth in the worm gear ÷ Number of threads in worm
WORMS GEARS–TOOTH DIMENSIONS
• Addendum – the distance from the pitch circle to the throat circle. (See Figure 4.9)
• Dedendum – the distance from the pitch circle to the base of the tooth. It is equal to the addendum plus the working clearance.
• Whole Depth – the distance between the throat and the base of the tooth. It is equal to the addendum plus the dedendum.
• Working Clearance – the space between the top of the worm thread and the bottom of the worm gear tooth when properly meshed.
SPECIAL ORDER WORM GEARS–PHYSICAL DIMENSIONS
When ordering special order worm gears, the pitch, number of teeth, pressure angle, number of threads, and the pitch diameter of the mating worm should always be specified.
