Wormgears are very important mechanical elements in the mechanical design of machinery. Wormgear sets allow the power transmission between non-parallel shafts. There is a helix-shaped tooth on the worm which is attached to a spur gear or helical gear.
In wormgears, proper assembly of teeth is very important. Very strict tooth design is required in both form worms and wormgears. There are various types of worm gears available according to the touching characteristics of assembled teeth.
Types Of Wormgears
In the single-enveloping type of wormgears, the contact between teeth is in a single line. This bigger contact allows the transmission of bigger loads and powers.
The second type of wormgear is called a double-enveloped type. In these types of worm gear sets, the contact between the worm gear and worm is only a point. There is no requirement for a strict placement of gears but the assembly between the worm gear set is very important to obtain proper alignment. These types of worm gears are generally used in low RPMs and low power transmission rates.
The Pitch Concept For Wormgears
In worm gear sets, the axial pitch of the worm must be equal to the circular pitch of the gear. This is the first and most important condition for proper assembly between worm and worm gear.
The circular pitch of the gear is the distance between the specific points on adjacent teeth on the pitch diameter. Axial pitch is also the distance between specific points of adjacent teeth on a worm.
Circular Pitch Calculator
To calculate the circular pitch of your gear in wormgear set, just enter the required parameters inside the barckets. You need to enter ‘Pitch Diamater Of Gear’ and ‘Number Of Teeth In Gear’. Then click on ‘Calculate!’ button to calculate the ‘Circular Pitch’ value of your gear.
If you want to make another calculation, just click on ‘Reset’ button then re-enter the required values.
You can also find the diametral pitch of your gear by dividing the diametral pitch value with number of teeth.
To calculate the circular pitch of your gear in a worm gear set, just enter the required parameters inside the brackets. You need to enter ‘Pitch Diameter Of Gear’ and ‘Number Of Teeth In Gear’. Then click on the ‘Calculate!’ button to calculate the ‘Circular Pitch’ value of your gear.
If you want to make another calculation, just click on the ‘Reset’ button then re-enter the required values.
You can also find the diametral pitch of your gear by dividing the diametral pitch value by a number of teeth.
Geometric Features Of Worm And Calculations Of Them
If you take a look at the other types of gears available in Mechanical Base, the geometry of a worm is quite different. To illustrate and represent the worm in terms of engineering, we need to understand some geometrical terms about the worm.
Lead Of Worm
The lead of the worm is a very important geometrical parameter. When the worm is rotated in one revolution, the lead of the worm is described as the axial distance of a point that moves with this one rotation.
You can find the lead of a worm by multiplying the axial pitch of the worm and the number of threads. The number of threads on the worm can be 1 to 8 or 10, it changes according to manufacturer standards.
Lead Angle Of A Worm
The lead angle value of a worm is an actually important geometrical parameter. This is basically the angle of threads according to the line that perpendicular to the axis of the worm. You can calculate it by using the calculator below;
Lead Angle Calculator For Worm
You need to enter the lead of the worm and the pitch diameter of the worm inside brackets to calculate the lead angle value of a worm.
Pressure Angle Of Worm Gears
For wormgears, the pressure angle and lead angle values are proportional. For low lead angles, low-pressure angles are preferred to prevent interference. For higher values, higher values of pressure angles are available.
For example, for pressure angles, 14,5 degrees, 17 degrees of lead angles are available in the general market. 25 degrees of pressure angles are used to obtain 35-40 degrees of lead angle values.
Self-Locking Phenomenon In Worm Gears
This is a very important phenomenon that occurs in worm gear sets. For different applications, self-locking of worm gear sets can be both desired or not desired.
Self-locking of worm gears is actually the locking of the system when the rotation comes from gear. To accomplish rotation, the power must come from the worm.
The complete self-locking can be achieved lead angles below about 5 degrees. The lead angles higher than 5 degrees may not produce a self-locking phenomenon.
Worm Diameter Suggestion
In general, smaller worms are desired in designs. For most designs, you can use the equation below that gives the suggested range;
1.5 < (R^0.875)/Dw < 3.3
Here, R is the distance between the centers of the mating worm and worm gear and, Dw is the pitch diameter of the worm.
In general, also, manufacturers produce worms with a bored hole through the center to assemble shafts, which they can not fall in this range. But, you can go on with the manufacturer standards of worms.
The geometries of worm gears are very important and very complex. For most of the time, you will use standard sized and dimensioned worm gears and gear sets.
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