Worms and Worm Wheels

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WORM GEARS

The arrangement of gears seen below, is called a worm and worm wheel. The worm has one helical tooth that looks like a screw thread. The worm wheel is a gear wheel with helical teeth, cut at an angle matching the worm. The worm always drives the worm wheel round, it is never the opposite way round, because the system tends to lock and jam.

The worm, which in this example is brown in colour, only has one tooth but it is like a screw thread. The worm wheel, coloured yellow, is like a normal gear wheel or spur gear. T

The picture below show the typical set up of worm gear system, as seen in school projects. As the worm revolves the wormwheel (spur gear) also revolves, with motion is transmitted through a ninety degree angle.

INDUSTRIAL WORM GEAR MOTORISED SYSTEM

SECTIONED VIEW - REALISTIC SCALE

TYPICAL WORM GEAR AND MOTOR USED IN SCHOOL PROJECTS




The gear ratio of a worm gear is worked out through the following formula: number of teeth on wormwheel number of teeth on worm The worm acts as a single toothed gear so the ratio is; number of teeth on wormwheel 1
EXAMPLE: If the wormwheel has 60 teeth: 60 1 Gear Ratio = 60:1 (Rotary velocity is also reduced by 60:1)
Quite simply, this means a worm gear reduces the speed of the spur gear by sixty times. If you need a gear system whereby the speed is reduced by a considerable amount - a worm and wormwheel are worth considering.

DETAILED DIAGRAM OF A WORM WHEEL AND WORM



ADDITIONAL QUESTION

1. Describe how a worm and wormwheel could be used as part of a design for a mechanical device or toy. Use diagrams and notes. 2. If the wormwheel has 80 teeth, what is the gear ratio ?




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