UNIT 1

Drawing Standards And Geometrical Construction

1. Difference between IS and SP standards.

2. List out various types of lines and their application.

3. What are line thickness used in making drawings?

Two thicknesses of lines are used in draughting practice. The ratio of the thick to thin line should not be less than 2:1. The thickness of lines should be chosen according to the size and type of the drawing from the following range: 0.18, 0.25, 0.35, 0.5, 0.7, 1, 1.4 and 2.

4. When should leader line terminate?

Leader lines should terminate

(a) with a dot, if they end within the outlines of an object,

(b) with an arrowhead, if they end on the outline of an object,

(c) without dot or arrowhead if they end on a dimension line.

5. List out general principles for dimensioning.

Ans - 1. As far as possible, dimensions should be placed outside the view.

2. Dimensions should be taken from visible outlines rather than from hidden lines.

3. Dimensioning to a centre line should be avoided except when the centre line passes

Through the centre of a hole.

4. Each feature should be dimensioned once only on a drawing.

5. Dimensions should be placed on the view or section that relates most clearly to the

Corresponding features.

6. Each drawing should use the same unit for all dimensions, but without showing the

Unit symbol.

7. No more dimensions than are necessary to define a part should be shown on a drawing.

6. Methods of indicating dimensions.

I. Aligned system:

Dimensions should be placed parallel to their dimension lines and preferably near the middle, above and clear-off the dimension line.

Chain dimensions:

Chains of single dimensions should be used only where the possible accumulation of tolerances does not endanger the functional requirement of the part.

7. Conventions used during scaling?

Scale is the ratio of the linear dimension of an element of an object as represented in the drawing, to the real linear dimension of the same element of the object itself. Wherever possible, it is desirable to make full size drawings, to represent true shapes and sizes. If this is not practicable, the largest possible scale should be used. While drawing exceedingly small objects, such as watch components and other similar objects, it is advisable to use enlarging scales.

If all drawings are made to the same scale, the scale should be indicated in or near the title block. Where it is necessary to use more than one scale on a drawing, the main scale only should be shown in the title block and all the other scales, adjacent to the item reference number of the part concerned or near the drawings.

8. How to bisect a given angle?

To bisect an angle

Let ABC be the given angle.

(i) With B as centre and any radius, draw an arc cutting AB at D and BC at E.

(ii) With centres D and E and the same or any convenient radius, draw arcs intersecting each other at F.

(iii) Draw a line joining B and F. BF bisects the angle ABC, i.e. ∠ABF = ∠ FBC.

9. How to draw a regular polygon given one side?

To construct a regular polygon, given the length of its side.

(i) Draw a line AB equal to the given length.

(ii) With centre A and radius AB, draw a semi-circle BP.

(iii) With a divider, divide the semi-circle into seven equal parts (same as the

Number of sides). Number the division-points as 1, 2, etc. starting from P.

(iv) Draw a line joining A with the second division-point 2.

10. Method for constructing a pentagon.

To construct a pentagon, length of a side given.

Method I:

(i) Draw a line AB equal to the given length.

(ii) With centre A and radius AB, describe a circle 1.

(iii) With centre B and the same radius, describe a circle-2 cutting circle-1 at C and D.

(iv) With centre C and the same radius, draw an arc to cut circle-1 and circle-2 at E and F respectively.

(v) Draw a perpendicular bisector of the line AB to cut the arc ff at G.

(vi) Draw a line EC and produce it to cut Q circle-2 at P.

(vii) Draw a line FG and produce it to cut circle-1 at R.

(viii) With P and Ras centres and AB as radius, draw arcs intersecting each other at Q.

(ix) Draw lines BP, PQ, QR and RA, thus completing the pentagon.