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Worm drive
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Worm drive
A worm drive is a gear arrangement in which a worm (which is a gear in the form of a screw) meshes with a worm wheel (which is similar in appearance to a spur gear). Its main purpose is to translate the motion of two perpendicular axes or to translate circular motion to linear motion (example: band type hose clamp).The two elements are also called the worm screw and worm gear. The terminology is often confused by imprecise use of the term worm gear to refer to the worm, the worm wheel, or the worm drive as a unit.
The worm drive or "endless screw" was invented by either Archytas of Tarentum, Apollonius of Perga, or Archimedes, the last one being the most probable author. The worm drive later appeared in the Indian subcontinent, for use in roller cotton gins, during the Delhi Sultanate in the thirteenth or fourteenth centuries.
A gearbox designed using a worm and worm wheel is considerably smaller than one made from plain spur gears, and has its drive axes at 90° to each other. With a single-start worm, for each 360° turn of the worm, the worm wheel advances by only one tooth. Therefore, regardless of the worm's size (sensible engineering limits notwithstanding), the gear ratio is the "size of the worm wheel - to - 1". Given a single-start worm, a 20-tooth worm wheel reduces the speed by the ratio of 20:1. With spur gears, a gear of 12 teeth must match with a 240-tooth gear to achieve the same 20:1 ratio. Therefore, if the diametrical pitch (DP) of each gear is the same, then, in terms of the physical size of the 240 tooth gear to that of the 20 tooth gear, the worm arrangement is considerably smaller in volume.
The entire drive (both worm and wheel) can be classified as follows:
These classifications refer to the worm itself:
Unlike with ordinary gear trains, the direction of transmission (input shaft vs output shaft) is not reversible when using large reduction ratios. This is due to the greater friction involved between the worm and worm wheel, and is especially prevalent when a single-start (one spiral) worm is used. This can be an advantage when it is desired to eliminate any possibility of the output driving the input. If a multi-start worm (multiple spirals) is used, then the ratio reduces accordingly, and the braking effect of a worm and worm wheel may need to be discounted, as the wheel may be able to drive the worm.
Worm drive configurations in which the wheel cannot drive the worm are called self-locking. Whether a worm drive is self-locking depends on the lead angle, the pressure angle, and the coefficient of friction.
The invention of the worm drive is attributed by some to Archimedes during the First Punic War, wherein the size of the ships being built necessitated a much larger crane than was available at the time. The crane developed for this purpose utilised a worm drive and several magnifying gears and was named the barulkon. The description of this crane was recorded in the Library of Alexandria, and subsequent engineers would draw upon Archimedes' ideas until the first technical drawings of a worm drive were developed by Leonardo da Vinci; the design was limited by the fact that metallic gears had not been invented by the advent of the 15th century, and the drive was never built in his lifetime.
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Worm drive AI simulator
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Worm drive
A worm drive is a gear arrangement in which a worm (which is a gear in the form of a screw) meshes with a worm wheel (which is similar in appearance to a spur gear). Its main purpose is to translate the motion of two perpendicular axes or to translate circular motion to linear motion (example: band type hose clamp).The two elements are also called the worm screw and worm gear. The terminology is often confused by imprecise use of the term worm gear to refer to the worm, the worm wheel, or the worm drive as a unit.
The worm drive or "endless screw" was invented by either Archytas of Tarentum, Apollonius of Perga, or Archimedes, the last one being the most probable author. The worm drive later appeared in the Indian subcontinent, for use in roller cotton gins, during the Delhi Sultanate in the thirteenth or fourteenth centuries.
A gearbox designed using a worm and worm wheel is considerably smaller than one made from plain spur gears, and has its drive axes at 90° to each other. With a single-start worm, for each 360° turn of the worm, the worm wheel advances by only one tooth. Therefore, regardless of the worm's size (sensible engineering limits notwithstanding), the gear ratio is the "size of the worm wheel - to - 1". Given a single-start worm, a 20-tooth worm wheel reduces the speed by the ratio of 20:1. With spur gears, a gear of 12 teeth must match with a 240-tooth gear to achieve the same 20:1 ratio. Therefore, if the diametrical pitch (DP) of each gear is the same, then, in terms of the physical size of the 240 tooth gear to that of the 20 tooth gear, the worm arrangement is considerably smaller in volume.
The entire drive (both worm and wheel) can be classified as follows:
These classifications refer to the worm itself:
Unlike with ordinary gear trains, the direction of transmission (input shaft vs output shaft) is not reversible when using large reduction ratios. This is due to the greater friction involved between the worm and worm wheel, and is especially prevalent when a single-start (one spiral) worm is used. This can be an advantage when it is desired to eliminate any possibility of the output driving the input. If a multi-start worm (multiple spirals) is used, then the ratio reduces accordingly, and the braking effect of a worm and worm wheel may need to be discounted, as the wheel may be able to drive the worm.
Worm drive configurations in which the wheel cannot drive the worm are called self-locking. Whether a worm drive is self-locking depends on the lead angle, the pressure angle, and the coefficient of friction.
The invention of the worm drive is attributed by some to Archimedes during the First Punic War, wherein the size of the ships being built necessitated a much larger crane than was available at the time. The crane developed for this purpose utilised a worm drive and several magnifying gears and was named the barulkon. The description of this crane was recorded in the Library of Alexandria, and subsequent engineers would draw upon Archimedes' ideas until the first technical drawings of a worm drive were developed by Leonardo da Vinci; the design was limited by the fact that metallic gears had not been invented by the advent of the 15th century, and the drive was never built in his lifetime.
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