Sectional Views?

Question

Why and when sectional views are required? Could anyone tell me the steps to draw an arc tangent to two circles?

Other than broken-end section, revolved section and half section, are there any other types of section??? If possible, please give an example of when each is drawn.

Answer 1

*Please go through following link for arc-tangent:
http://archicad-talk.graphisoft.com/viewtopic.php?p=39826

Step1: Given two circles with centers marked C1 and C2, move a triangle or straightedge to connect the centerlines. 2 Place a triangle at the upper arcs of the circles until one side of the triangle touches both circles C1 and C2. Draw a line tangent to the circles.
3 Draw a perpendicular line from the points of tangency to the centerlines of the circles.
4 Repeat this procedure for the bottom arcs of the two circles.

*A cross section is a common method of depicting the internal arrangement of a 3-dimensional object in two dimensions. It is often used in technical drawing and is traditionally crosshatched. The style of crosshatching indicates the type of material the section passes through.

In geometry, a cross section is the intersection of a body in 2-dimensional space with a line, or of a body in 3-dimensional space with a plane, etc. More plainly, when cutting an object into slices one gets many parallel cross sections.

A cross section, or section is also an orthographic projection of a 3-dimensional object from the position of a plane through the object. A floor plan is a section viewed from the top. In such views, the portion of the object in front of the plane is omitted to reveal what lies beyond. In the case of a floor plan, the roof and upper portion of the walls may be omitted.

Elevations or roof plans are orthographic projections, but they are not sections as their viewing plane is outside of the object.

http://en.wikipedia.org/wiki/Cross_section_(geometry)
*Section Views :
Full Section
Half Section
Offset (Sketched) Section
Revolved Section
Broken Out (Local) Section
Detailed Views
Conventional Breaks

Answer 2

Think of a Plan(or a Floor Plan), as a view looking down on a building with the roof removed. A sectional view of this floor plan would be required when you need to show detail that is not visible in the Floor Plan. For example, let's say you have two same size pipes running parallel to eachother, one above the other. You would only see the top pipe in the Floor Plan. A sectional view would show the two pipes as two circles, one above the other. The sectional view could also show other details such as the size and elevations of the pipes.
There are several cases to consider when discussing drawing a circle or arc tangent to two circles. One circle could be inside the other, or the circles could be intersecting. Lets look at the case where the two circles are exterior to eachother. Let the two circles be A, and B. And let the radii of the circles be Ra and Rb respectively. Many arcs can be drawn tangent to both circles. Also, let d be the distance between the two circles. The diameter of the required arc must be greater than d. Choose a radius for the required arc and call it Rc. Geometrically add Ra + Rc and Rb + Rc. Scribe an arc of radius Ra + Rc centered at the center of circle A. Scribe an arc of radius Rb + Rc centered at the center of circle B. These two arcs will intersect in two distinct points, the two possible centers of your required arc.

cpl_cpl's procedure is for finding a line tangent to two given circles.

Answer 3

in case of a building we need its each parts length breadth and height for the estimation. when we are cutting an object and view from the sides we are getting its sectional veiws .
In some calculation we have to know the depth of the structure
in such a case sectional views are required.