As shown in Figure 6.1, a high ratio speed reduction in a small space can be obtained compared to spur gears. The mating gear is called a worm wheel together they are called worm and worm wheel or simply worm gear (worm gear device). There are one or more teeth which are screw shaped, resulting in a gear that looks like a worm. Worm gear is one type of gear device in which the two shafts are at a right angle or near right angle and non-intersecting.
Masao Kubota, Haguruma Nyumon, Tokyo : Ohmsha, Ltd., 1963. This article is reproduced with the permission. You can confirm the combinations of the KHK’s standard worms and worm gears in an enlarged table. Mating worm : KWGDL, KWGDLS Click Here to Select Worm Gears Click Here to Duplex Worm Guide Click Here to E-series for AGDL Table of Worm and Worm Gear Combinations Used in combination with KWGDL or KWGDLS. However, since it is not a totally dependable function, it is desirable to use it in combination with another method when a total prevention of reversal is required.Įxamples of worm gear applications include speed reducers, elevators, machine tools, chain blocks, fishing reels and automotive power steering.ĭuplex worm wheels made of aluminum bronze with excellent accuracy and a good balance between machinability and wear resistance. This condition is called self-locking, and the result of preventing the reverse motion is expected. When the worm's lead angle is especially small, it becomes impossible to turn the worm by the worm wheel.
When using a worm gear, the worm is the driver and the worm wheel is the driven shaft. In cases, such as when tooth wear produces the need for readjustment of the backlash, it can be accomplished without changing the center distance between worm and worm gear. When using the latter type worm gear, it is possible to move the worm axially by a shim which allows the adjustment of backlash. The lead of the left and right tooth surfaces of the worm is normally equal, however there is also another type called dual-lead worm gear which is made with a different lead for the two surfaces. are used for worms, while cast iron (FC200), phosphor bronze and aluminum bronze, and MC nylon (an engineering plastic) are used for the worm wheel. To reduce wear, worms are generally made of a harder material than worm wheels.įor KHK standard gears, mechanical structural carbon steel (S45C), mechanical structural alloy steel (SCM440), stainless steel, etc. Worm gears have advantages such as low noise and low vibration, but because power transmission is effected by sliding contact, it also has the disadvantage of retaining heat and its transmission efficiency is not high (in the case of a cylindrical worm gear, the general efficiency is about 30 - 60%). For example, in the case of the worm gears of the KHK's standard gears, a reduction ratio of up to the maximum of 1/120 can be obtained. The reduction ratio is determined by the combination of the number of worm threads and the number of teeth on the worm wheel. When a worm gear is used, a compact and high speed reduction ratio can be obtained as compared with spur gears. The latter type is also called "throated worm gear". The other is the "drum-shaped worm gear" which is a pair consisting of a drum-shaped worm and a worm wheel. One is a cylindrical worm that meshes with a worm wheel as a pair to form the "cylindrical worm gear". There are roughly two types of worm gears. Its history is so old that its existence is described by Archimedes in around 250 BC. The set of a worm and worm wheel is called a worm gear.
Even though it is compact it can provide a large speed reduction.Ī worm gear is a thread cut into a round bar, and a worm wheel is a gear that meshes with the worm at a shaft angle of 90 degrees. A worm gear is a type of staggered shaft gear that transmits motion between two shafts that are neither intersecting nor parallel.