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|FCGear → Create a Worm gear|
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|PartDesign: Ingranaggio a spirale|
The worm can be considered a special case of a helical gear. Imagine that there is only one tooth on a spur gear. Now increase the helix angle so much that the tooth winds around the spur gear several times before it emerges on the opposite side. The result would be a single thread worm.
For a single-start worm, each full turn (360 degrees) of the worm advances the gear by one tooth. So a gear with 24 teeth will provide a gear reduction of 24:1. For a multi-start worm, the gear reduction equals the number of teeth on the gear, divided by the number of starts on the worm.
A worm can only be used with a worm wheel. This is called a worm drive. Like other gear arrangements, a worm drive can reduce rotational speed or transmit higher torque. One of the major advantages of worm gear drive units are that they can transfer motion in 90 degrees. A worm drive is also self-locking.
- Switch to the FCGear Workbench.
- Invoke the command several way:
- Press the Create a Worm gear button in the tool bar.
- Using the Gear Menu → Worm gear.
- Change the gear parameter to the required conditions (see Properties → Data below).
- DataPlacement: Placement is the location and orientation of an object in space.
- DataLabel: User name of the object in the Tree view.
- Databeta: Lead angle, not changeable - is calculated automatically (see also the information in Notes and Useful formulas).
- Dataclearance: Default is 0,25 (see also the information in Notes).
- Datadiameter: Pitch diameter.
- Datahead: Default is 0,00. This value is used to change the tooth height.
- Dataheight: Value of the worm length.
- Datamodule: Module is the ratio of the reference diameter of the gear divided by the number of teeth (see also the information in Notes).
- Datareverse_pitch: True change the rotating direction from right to left.
- Datateeth: Number of teeth (see also the information in Notes).
- Datapressure_parameter: Default is 20 (see also the information in Notes).
The parameter descriptions of the View tab will be found in Property editor, further below at Example of the properties of a PartDesign object.
- beta: If the lead angle is less than 5°, it is a self-locking gear. A typical example are the tuning pegs on a guitar or ukulele.
- clearance: At a worm gearing, clearance is the distance between the tooth tip of the worm and the tooth root of the worm wheel.
- module: Using ISO (International Organization for Standardization) guidelines, Module size is designated as the unit representing gear tooth-sizes. Module (m): m = 1 (p = 3.1416), m = 2 (p = 6.2832), m = 4 (p = 12.566). If you multiply Module by Pi, you can obtain Pitch (p). Pitch is the distance between corresponding points on adjacent teeth. If the module is changed, the lead angel also changes (beta).
- teeth: The number of teeth in a worm is called the number of threads. Correspondingly, one speaks of single, double or multiple thread worms. In general, mainly single worms are produced, but in special cases the number of starts can be up to four (sometimes also more). If the number of teeth is changed, beta also changes.
- pressure_parameter: Only change the parameter, if sufficient knowledge of the gear geometry is available.
Limitation are not known yet.
- beta (lead angle) = arctan (module * teeth : pitchdiameter (diameter))
- axial pitch = pi * module * teeth
- beta (lead angle) = arctan (axial pitch : (pitchdiameter (diameter) * pi))
- worm length = 4,5 * module * pi
The worm wheel must be designed manually. For this purpose FCGear InvoluteGear can be used for a simple construction. In any case, in-depth knowledge of the gear types is required.