1. Why use a worm and wheel system?

This type of arrangement offers a very high reduction in speed and under certain conditions exhibits anti-backdrive characteristics. The basic efficiency of the system is low but increases in proportion to the angle of the teeth. The worm and wheel both have the same helix direction.

2. What can I do if the wheel in a worm and wheel system is damaged or worn?

There is no standardisation of worms and wheels between different manufacturers. If one part is damaged it must be replaced by a strictly identical piece, this normally means having a copy made of the faulty piece. Manufacturers are free to choose the diameter of the thread and it is this determines the helical angle, the PCD (Pitch circle diameter) and distance between centres.

3. What are anti-backlash wormwheels?

As their name indicates, these wheels allow the absorption of the backlash which can exist in a classical worm and wheel setup. Springs are placed in channels between two wheels of the same dimension, which are attached together with a circlip. During assembly the two discs should be offset by a few degrees, this compresses the springs and allows them to absorb any backlash.

Note, anti-recoil wormwheels can be only used with single start worms.

4. Can you supply custom made worms and wheels?

Yes we can supply custom made worm and wheel pairs, please contact us on +33 (0) 437 496 496

5. How do I determine the principal characteristics of a worm and wheel pair?

Worm(screws)

Four principal parameters characterise a worm

• the thread p
• the number of starts Z
• the external diameter d
• the direction of the teeth and the helix angle
  These parameters are related by a complex mathematical calculation

The actual helix angle is difficult to determine. The direction of the teeth is done visually. Hold the gear vertically, if the threads go up to the left, it is a left handed thread, if they go up to the right, it is a right handed thead.

left hand threaded	right hand threaded

To measure the pitch, measure the distance between two threads.

To count the number of threads, it is necessary to count the number of starts by looking at the end of the thread or into the bore.

Don't count the starts like this	They should be counted in this direction

For wormwheels

There are 4 principal characteristics that define a wheel

• the pitch m
• the number of teeth Z
• the external diameter de
• the teeth's slant direction and helix angle

The first three parameters are determined by the formulae
de = m x (Z+2) or m = de/(Z+2) or Z = (de/m)-2

The actual helix angle is difficult to determine. The direction of the teeth is done visually. Lay the the gear on a table, if the threads go up to the left, it is a left handed thread, if they go up to the right, it is a right handed thead16       The helix angle is difficult to measure. The only way is to assemble the wheel with the worm that was made for it (same module and same number of threads).

This worm with 4 threads will not function with the gear with only 1 thread.	However this worm and wheel are compatible.