Line of action
The pressure angle actually resulting during operation is called the operating pressure angle α b (the index b is used because the line of action to which the operating pressure angle refers results as a tangent to the base circles of the gears). However, if the center distance changes or gears with profile shifts are used, the pressure angle will change and then differ from the standard pressure angle. The standard pressure angle will be automatically obtained for non-profile shifted gears during backlash-free pairing. Animation: Influence of the standard pressure angle on the tooth shape For more information see article Geometry of involute gears. The tooth shape is thus decisively determined by the standard pressure angle. For example, a standard pressure angle of 20° means that the flanks of the hob must also be inclined by 20° to produce the tooth flanks. This standardization of the pressure angle α 0 is particularly important for the tool geometry in gear manufacturing, since the flank angle of the rack-shaped cutting tool ( hob) depends on it. In such a case, the center distance is called standard center distance a 0 and the resulting operating pitch circles are called standard (reference) pitch circles. In this standard state, the pressure angle is also referred to as the standard pressure angle α 0 (=20°). The so-called pressure angle α b refers to the angle between the normal of the line of centers and the line of action. For a standard gear, this pressure angle is set to 20° with backlash-free pairing of the teeth. The distance actually covered on the line of action is then called line of contact (red line in the animation above). The line of contact begins at the intersection A between the line of action and the addendum circle of the driven gear and ends at the intersection E between the line of action and the addendum circle of the driving gear. The line of action corresponds to the tangent applied on the base circles of the gears. Animation: Line of action (line of contact) during meshing This line of action corresponds in principle to the rolling line for the construction of the involute tooth flanks. This straight line is also referred to as the line of action or line of engagement. The involute tooth flanks then slide along a straight line (black line in the animation below). This situation occurs when two gears are meshing.
![line of action line of action](https://javicandraw.com/wp-content/uploads/2016/09/03-2-705x497.jpg)
In Two in a Room (see the section on Dialogue) the through-line is “to survive”. The through-line enables both actor and director to narrow down the possibilities of action into core playable coherent concepts, providing clear motivation and direction to the actors in the way they perform an action or speak a line. What exactly is the through-line or spine? The spine is a key idea or purpose of the play expressed as an action (usually a verb) which links all elements of the script (style, character, dialogue, action) and gives a coherence to the piece. In establishing a spine, the writer therefore makes every aspect of the play purposeful in terms of performance.
![line of action line of action](https://live.staticflickr.com/3480/4005110690_788fa7267e_b.jpg)
It helps the author create a vehicle for actors by enabling the writer to decide what is theatrically important and what is textually superfluous in the script. It is linked to the theme or central idea of the play. This idea of a textual spine is a useful editing tool for the writer, too. The through-line of action (also called the spine) is one method used by actors and directors to give a performance direction.