How to design worm gearbox ( worm gear motor design )

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How to design worm gearbox (WGM-370 desgin share)

1.1 What is a worm gear?

Worm gear system is one of the most commonly used gear reduction structure, which transmits power and increases torque through the meshing of a threaded worm with a gear. The main gear method of the micro worm gear box is to process the end of the motor shaft into the thread of the worm, and use the motor shaft as the worm to mesh with the internal gear . The basic structure is shown in the figure.

2.1 How to calculate the worm gear ratios

The difference between worm gear system and spur gear system is to add the gear system of worm and gears. How to calculate the gear ratio is an important part of the design of the worm gear box.

As the figure show,  the worm on the shaft has only 1 tooth and the worm wheel is a normal spur gear.

Basic formula:

Gear ratio=number of teeth on wormwheel/ number of teeth on worm

The worm regards as a single toothed gears so the functions is:

Gear ratios= number of teeth on wormwheel/ 1

Therefore, the gear ratio of the worm gear reduction is determined by the number of teeth on the worm.

3.1 The advantages of worm gear

Compare with the spur gear system and planetary gear system, worm gear system give engineers more choice during the design period. Here are some reasons why engineers choose to use worm gearbox.

1: 90°shaft: The worm gear reduction system changes the direction of the transmission, and the miniature worm reducer can achieve 90° out of the shaft. This provides engineers with more choices for different use environments.

2: Self locking: n the worm gear reduction system, when the input end stops input, the gearbox will have a self-locking function, which is caused by the friction between the worm wheel and the worm. With the same reason, compared with the spur gear reducer and the planetary reducer, the worm gear reducer cannot rotate in the opposite direction.

3: Higher gear ratio: According to the formula, engineers could increase the gear ratio of the worm gearbox through increase the tooth of worm wheel. It is a huge advantage of worm gear reduction, which means that the worm gear reducer can use fewer components to output higher torque.

4.1 Processing Stage

1: Worm processing: The motor output shaft uses a 40 Cr carbon steel non-integrated shaft with machined threads to form a worm at the end of the output shaft.

2: Gears processing: There are 3 kinds of gear materials commonly used in worm gear system including: plastic, gear hobbing, power metallurgy. According to the requirements of the product’s torque, noise, life, strength, etc., engineers will provide different gears to match different product requirements.

4.2 Advantages and disadvantages of different gear materials.

Plastic gear:

Good: Low noise and low cost.  

Bad: plastic gears have low strength and small torque. They are easily damaged.


Gears hobbing:

Good: High gear strength and controllable precision.

Bad: High cost


Power metallurgy:

Good: Low price and simple production

Bad: High noise and low gear strength

5.1 WGM-370 Structure


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