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Please leave this field empty. Get a Quote. Gear Motions. Gear Motions » Blog » Helical Gears vs. Spur Gears. Helical Gears vs. Worm gears come with certain disadvantages though. The transmission efficiency is not as good compared to other gears. Also, the fact that sliding occurs between the worm and worm wheel during transmission makes lubrication a factor to pay attention to. Continuous lubrication is the basis for smooth operation.
Now that we have a general idea of the different types of gears, we are in a better position to get a bit technical and understand the meaning of various terms that one may come across while learning about gears. This is the maximum diameter of a gear. It is the distance from the gear body centre to the tooth tip.
The outer diameter signifies the outermost extent of a gear. The pitch circle of two engaging gears touch each other at the point where the mating teeth come in contact with each other. It runs roughly around the centre of the gear tooth. Pitch circle is where the motion transfer takes place and hence, this circle is used for all calculation purposes. The point at which the gears touch is known as pitch point. It is the distance between the centres of two mating gears of a system.
It is important that this distance is set properly for effective transfer of torque. It is calculated by adding the pitch circle diameter of the two gears and dividing by two. Root is the point where the tooth connects to the gear body.
It is the trough between the bottom-most part of two adjacent gear teeth. Root diameter is the distance between the centre of a gear body and the base of a gear tooth.
Pitch is defined as the distance between the same point on two adjacent gear teeth. It can be calculated easily by dividing the circumference of the gear at that point by the number of teeth.
Thus, the diameter needs to be specified. Some popular pitches are circular pitch, normal base pitch, and angular pitch. Circular pitch is the distance between the same points on two teeth faces along the pitch circle. Diametral pitch informs us of tooth density. It is calculated by dividing the total number of gear teeth by the pitch circle diameter. Its unit is the number of teeth per meter. Tooth profile refers to the shape of a gear tooth.
There are many different options we can choose from. We could make them rectangular, triangular, in the shape of a circular arc, or move on to more complex shapes such as a parabola or an involute. Simple shapes such as rectangles and triangles, however, create high vibration, noise, and would be very inefficient due to excessive sliding.
Complex shapes improve efficiency and enable quiet operation. It is the most widely used tooth profile. There are certain advantages of using involute gears, such as:. The cycloidal tooth profile is the second most common profile in use. This profile ensures the same wear occurs on the entire tooth.
Cycloidal gear teeth find use in watches and instruments. It is seldom used for intensive applications as it is difficult to produce. This profile is not as popular but it has the advantage of slow wear as the arc is uneven. It is classified into two types: single arc and compound arc. As the name suggests, the tooth has a cylindrical shape which mates with the other gear.
Sometimes, a convex arc may fit into a concave arc for better transmission. This profile, however, is difficult to produce compared to the involute profile.
Gears are produced using a variety of material and this selection will also affect the surface treatment method that may be chosen to improve performance. Gears may be produced from different types of metals as well as non-metals such as steel, cast iron, plastic, nylon, and fibre. Each material has its own salient features:. Surface treatment of gears is usually necessary before putting them into service. Two useful techniques for gear surface finishing are grinding and heat treatment.
Grinding gear teeth makes them smooth and leads to quiet operation. It does increase the final cost of production though. Many heat treatment techniques are available for improving the strength, surface finish, and durability of gears.
Some of these procedures are carburising, annealing, tempering, surface hardening, and normalising. Depending on the material used and procedure employed, the gears can be made strong, heat-resistant, hard, and durable.
What happens is that the for the two gears contact takes place only in a point, and not a line. The difference between transverse module and normal module is defined as the difference of basic tooth form. As shown in the figure below the module of tooth datum orthogonal to the center axis of gear is called transverse module.
The module of tooth datum orthogonal to the thread helix is called normal module. Difference between normal and transverse module. The characteristics of each module is Shown below. Style Advantage Disadvantage Transverse module Replaces spur gears having the same module, number of teeth, and center distance. Special gear cutting or grinding machines are required for processing each helix angle.
Normal module Modifications of spur gears are made by gear cutting or grinding machines, even if they have different helix angles. Because of the helix in the teeth of helical gears, while gears mesh thrust forces is developed in the axial directions. The axial thrust forces will force the gear to move towards the direction of bearing. Hence thrust bearing have to be placed in the direction of axial force. The axial thrust bearings must be able to resist the developed thrust forces.
The direction of the thrust forces depend on the helix hand and the direction of rotation as shown below.
If the gears have the same hands, the sum of the helix angles should equal the angle between the shafts. The most common example of this are crossed helical gears with perpendicular i. Both gears have the same hand, and the sum of their helix angles equals 90 degrees. For configurations with opposite hands, the difference between helix angles should equal the angle between the shafts. Crossed helical gears provide flexibility in design, but the contact between teeth is closer to point contact than line contact, so they have lower force capabilities than parallel shaft designs.
Helical gears are often the default choice in applications that are suitable for spur gears but have non-parallel shafts. They are also used in applications that require high speeds or high loading. Regardless of the load or speed, they generally provide smoother, quieter operation than spur gears.
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