Know about gear types and relations between the two shafts

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• Know about gear types and relations between the two shafts

Introduction

Recently, products with new and innovative structures are rarely developed. Rather, in most cases, only specification and design changes of existing models are done.
Therefore, it is desired of design engineers to acquire the skills to change some structures of existing models or parts to develop new products.
Design engineers should take responsibility in case of failure due to a major change of structure or part design because of arbitrary judgements of the engineer. Such are the current situations that most engineers just copy and paste using CAD without learning about principles of structure and mechanisms.

Incidentary, radio-cassette players and CD players, which were widely favored for a hobby or automobile use, had a reliable structure because of links, gears, and springs tightly arranged in a narrow space. Nowadays, we can play music only by inserting a USB or with wireless communication, and therefore all the machine design engineers need to design is a chassis containing non-moving parts to place an electronic substrate.
Such changes in our era also decreased machine design engineers’ opportunities to be exposed to mechanism design which eventually led to the lack of creativity to develop new structures and mechanisms.
Now, how should machine design engineers face mechanism design tasks when altering existing models and functions are weakened ?
In this chapter, basic knowledge of gears is explained before proceeding to invent mechanisms with gears.

1. Machine elements

Machine elements are the smallest units of functional parts (e.g. bolt, nut, gear, key, etc.) among components constituting a machine as shown in the table below (table 1-1).

Table 1-1 Machine elements

2．Types of drive transmission elements

Among machine elements, drive transmission elements are categorized into the following groups. (Table 1-2)

Table 1-2 Types of drive transmission elements

Drive transmission	Rigid contact transmission	Mesh transmission	Gears, etc.
		Friction transmission	Friction rollers, etc.
	Non-rigid contact transmission	Mesh transmission	Timing belts and chains
		Friction transmission	Flat belts, etc.
	Non-contact transmission	Magnetic power transmission	Magnet gears, etc.

Among these drive transmission elements, the mesh transmission gears are used for general mechanisms.

Gears are defined as “machine elements to transmit rotary motion by successively meshing the concave surface on one shaft with the convex surface (teeth) on the other shaft".

3．Gear functions

Here is the list of gear functions for mechanism designs. (Table 1-3)

Table 1-3 Gear functions

Characteristic functions of gears	Explanation
Change direction of rotating shaft	See this chapter
Convert rotary motion to linear motion	See this chapter
Change rotational direction (clockwise / counterclockwise)
Change the number of rotations (speed up / down)
Change turning force (increase / decrease torque)

Among various characteristics like shape, purpose, material, a designer first needs to review the layout of the two shafts on which gears are mounted.
The gear type determines the direction of the two shafts.
The layout of the gear shaft can be categorized into three as shown below. (Table 1-4)

Table 1-4 Gears by shaft layout

Let’s look at the types and characteristics of gears for the parallel shafts. (Table 1-5)

Table 1-5 Types and characteristics of gears for the parallel shafts

Now let’s look at the types and characteristics of gears for intersecting shafts. (Table 1-6)

Table 1-6 Types and characteristics of gears for intersecting shafts

Here are the types and characteristics of gears for skewed shafts. (Table 1-7)

Table 1-7 Types and characteristics of gears for skewed shafts

In the designing process, it is common to decide the layout of the two shafts before choosing the gear type. However, designers should consider that the cost of gears varies by the shaft layout as below.

1. Gears for parallel shafts (Cheap)
2. Gears for intersecting shafts
3. Gears for skewed shafts(Expensive)

We discussed gear functions as machine elements, and types and characteristics of gears in this section.

Next time, we will explain the principle of the speed ratio, one of the most crucial element of designing mechanisms with gears. (To be continued…)

Related links :
了解齿轮种类和两轴的关系

DISCLAIMER

The purpose of writing this article was to educate the readers with the elementary level of gear technology.
We hope that the actual design and manufacturing of gears and machinery utilizing gears are done with sufficient technical and specialized considerations under the user's full responsibility.
We disavow any liability and will not compensate for any direct or indirect damages caused by the gears designed by the users who read this article.