TOPIC : How drawings are controlled in industry in
relevance with various quality systems?
Submitted to Submitted by
Mr. Gurveen Singh Ankush
Roll No.- A 18
Reg. No.- 11001733
Section- B5005
CONTENTS
1. Introduction
2. System of Dimensioning
Aligned System
Undirectional System
3. Dimensioning Techniques
4. Dimensioning of Special feature
Diameter
Radii
Dimensioning holes
Counterbore holes
5. Conclusion
6. References
INTRODUCTION
A Drawing without dimensions is meaningless. Dimensions are necessary to
show the exact size of an object. Dimensioning refers to the act of giving
dimensions,i.e., length, width, height, diameter etc.of the object. This
information is provided by giving numeric values to various features of the
object on the drawing. A feature is an individual characteristic such as a flat or
cylindrical surface, a slot or a groove, a taper, a shoulder, a screw thread etc.
Units of Measurement
On technical drawing we need to show lengths and angels. The most convenient
unit for length is millimetre. In civil engineering and architectural drawing, inch
or foot is often used as a unit of length. Angels are shown in degrees.
Symbols
Symbols are incorporated to indicate specific geometery wherever necessary
SYSTEMS OF DIMENSIONING
For placing the dimensions on a drawing, one of the two systems mentioned
below is adopted.
Aligned System
In the aligned system, dimensions are placed perpendicular to the dimensions
line so that they may be read from the bottom or right-hand side of the drawing
sheet. All horizontal and inclined dimensions can be read from the bottom,
whereas vertical dimensions can be read from the right- hand side of the
drawing sheet. Dimensions are placed at the middle and on top of the dimension
lines.as pictorial dimensions
Drawings made with aligned dimensions have all figures and notes aligned with
a dimension line so that all read from the sides or edges of a drawing. The
most common are read from the bottom and right side. Aligned dimensions
are sometimes referred to as pictorial dimensions
Fig.1 . Aligned dimensions.
Unidirectional System
In the unidirectional system, dimensions are placed in such a way that they can
be read from the bottom edge of the drawing sheet. All horizontal dimensions
are placed at the middle and on the top of the dimension lines while vertical and
inclined dimensions are inserted by breaking the dimensions lines at the middle.
In the unidirectional dimension system, all dimension figures and notes are
lettered horizontally and are read from the bottom of the drawing. The
unidirectional dimension system is preferred over the aligned system because it
is easier to read and understand.
Fig2. Undirectional system
Dimension techniques
All dimension lines and arrowheads must lie in the planes of the object to which
they apply. Align dimensions and notes shown with leaders to the bottom of the
drawing. Notes without leaders should also align with the bottom of the
drawing. Use single-stroke gothic letters for dimensions and lettering on
drawings
For clear dimensions, follow these general rules:
Show sufficient dimensions to define size, shape, and position of each
feature.
Place dimensions on the view that most clearly represents the form of the
geometric component of the part.
Express each dimension so that it can be interpreted in only one way.
Place dimensions outside of the object outline except when it helps to
clarify.
Never use centerlines, object lines, or extension lines as dimension lines.
Select and arrange dimensions to minimize the accumulation of
tolerances between related features.
Do not double dimension. Do not locate a feature by more than one
tolerance dimension in any one direction.
Never cross dimension, extension, and leader lines unless absolutely
necessary.
Never break a dimension line except for inserting dimensions.
Never run an extension or leader line through a dimension line or break it
except where it passes through or is adjacent to arrowheads.
Avoid dimensioning to hidden lines. Express angular dimensions in
degrees (°), in minutes (´) and seconds (²), or in decimal parts of a degree.
Do not use zeros before the decimal point for values less than 1 inch.
Enclose dimensions in. parentheses or mark “REF” when it is (1)
repeated on the same drawing, (2) specified on subordinate documents,
(3) an accumulation of other dimensions, or (4) shown for information
only.
Do not use the word “TYPICAL” or the abbreviation “TYP.”
Instead, indicate (in parentheses) the number of places to which the
dimension applies (2 PLS).
Fig.3 Dimensions and Lettering
Dimensioning of Special Features
1. Diameter
When indicating the diameter of a circular shape, the diameter symbol (
Æ ) precedes all diametral values. When you must show the diameters
of a number of concentric or eccentric cylindrical features, dimension
them in a longitudinal or front view.
Fig.4 Dimensioning Diametric values
2. Radii
A radius is the distance between an arc and its center point. Indicate this
distance with a radius dimension line. A radius dimension line uses one
arrowhead at the arc end. Never use an arrowhead at the radius center
Fig.5- Radii with Centers
3. Dimensioning Holes
Where it is not clear that a hole goes through an object, the abbreviation
“THRU” follows the dimension. A blind hole is a hole that does not pass
completely through the object. The depth dimension of a blind hole is
the depth of the full diameter from the surface of the part. Where a blind
hole is also counterbored or counterdrilled, the depth dimension applies
from the outer surface.
Holes are dimensioned using leader lines pointing to the hole and shown
where the hole appears circular.
Dimensions and notes should always be lettered horizontally of the
drawing.
Fig.6- Dimensioning rounded holes
Fig.7- Dimensioning
4.Counterbored holes
Counterbored holes (CBORE) are holes of different depths that share holes
concentric centers. There is no angularity in the larger bore. Dimension
counterbored holes as two concentric diameters and a depth. Where the
thickness of the remaining material has significance, dimension the thickness
rather than the depth of the hole
Fig.8- Counterbore Dimension
Conclusion
At last engineering drawing is very useful in every field . By this we can
make the design of the particular object . We can easily dimension the
object like Diameter, Radii, Holes etc. The End goal of engineering
drawing is to convey all the required information that will allow a
manufacturer to produce that component.
REFERENCES
1. http://tpub.com
2. http://wikipedia.com
3. http://answers.com
