Engineering Drawing Method of Dimensioning

This Lecture covers dimensioning, and the rules followed in technical drawings as per BIS standards.
Suitable for First year B.Tech. students for Engineering subject.

1. ENGINEERING DRAWING
Dr Susanta Behera
Lecture-03
Dimensioning

2. Dimensioning
Exact length
Breadth
Height
Size
Position of holes and grooves
DIMENSIONING
•Necessary to show the exact size of an object
•A drawing without dimensionsis meaningless
Angle

3. TYPES OF DIMENSIONING
F : Represents functional dimensions
NF : Represents non-functional dimensions.
1.size or functional dimensions
2.location or datum dimensions

4. TERMS AND NOTATIONS
Dimension line
•Thin continuous line
•Terminated by arrowheads touching the outlines, extension lines or centrelines.
•To dimension an angle, a curved dimension line is drawn by drawing a suitable arc having
its centreat the vertex of the angle.
Extension line
•An extension line is also a thin continuous line drawn in
extension of an outline.
•B.I.S. Recommendation: 1 mm should be kept between the extension line and an outline
or object boundary.

5. TERMS AND NOTATIONS
Leader Line
•Leader line (or leader) is a line which connects a note or
a dimension with the feature to which it applies.
•Leaders are drawn at suitable angles, preferably 30°, 45°or
60°, and is never drawn horizontal or vertical.
Arrowheads
•An arrowhead is drawn at each end of a dimension line.
•Tip of the arrowhead touch the extension line.
•Size of arrowhead should be proportional to the thickness of the outlines
•Arrowhead may be open, closed, or closed and filled.
•Angle by the barbs of the arrowhead usually varies from 15°to 90°.

6. TERMS AND NOTATIONS
•Sometimes, an oblique stroke drawn at 45°to the extension line is used instead of an
arrowhead.
Note
•A note gives information regarding specific
operation relating to a feature.
•It is placed outside a view but adjacent to the
feature concerned.
•All notes should be written horizontally.

7. SYSTEMS OF DIMENSIONS

8. RULES OF DIMENSIONING
•Good dimensioning: clearness, completeness, readability and accuracy
•Dimensioning should be done so completely that further calculation or assumption of
any dimension, or direct measurement from the drawing is not necessary.
•Every dimension must be given, but none should be given more than once.
•A dimension should be placed on the view where its use is shown more dearly.
•Dimensions should be placed outside the views, unless they are clearer and more easily
read inside.
•Mutual crossing of dimension lines and dimensioning between hidden lines should be
avoided. Dimension lines should not cross any other line of the drawing.
•An outline or a centreline should never be used as a dimension line. A centreline may
be extended to serve as an extension line.
•Aligned system of dimensioning is recommended.

9. RULES OF DIMENSIONING

10. RULES OF DIMENSIONING

11. RULES OF DIMENSIONING
Dimensions in series
•Chain dimensioning (Continuous dimensioning)
•Parallel dimensioning (Progressive dimensioning)
•Combined dimensioning

12. RULES OF DIMENSIONING
Dimensioning Of Special Features
Dimensioning of Circular Features

13. RULES OF DIMENSIONING
‘5 x 18 (= 90)’ means that there are 5 + 1 = 6 holes, centre-to-centredistance between two
consecutive holes = 18 and distance between centresof first and last hole = 90. The break
lines may be used if there are a large number of holes on the uniform cross-sectioned area,
Equispacedholes (circles)
Equispacedangular spacing holes and holes on a pitch circle

14. RULES OF DIMENSIONING
Arc dimensioning
Cylindrical features

15. RULES OF DIMENSIONING
Dimensioning of Spherical Features
Conical and Tapered Features

16. RULES OF DIMENSIONING
Flat tapered features
Dimensioning of Square Features
Square features (e.g., a rod of square cross-section) are dimensioned using symbol □or SQ
If the true shape of the square is not seen in the view, then cross lines are used to indicate
the square cross-section

17. RULES OF DIMENSIONING
Dimensioning of Chamfered Features
Dimensioning of Countersunk

18. RULES OF DIMENSIONING
Dimensioning of Screw Threads
External metric threads are dimensioned by giving the threaded length and nominal
diameter preceded by symbol ‘M ’,
Internal metric threads are dimensioned by giving the threaded length, depth of drilled
hole before threading and nominal diameter preceded by symbol ‘M ’,