Page 33 - CITS - ED - Mechanical

ENGINEERING DRAWING - CITS

• Draw a circle of diameter 40 mm, divide it into 12 equal parts and number them as 1,2.....12.
• Draw vertical projectors of sufficient length (more than 60 mm) from points 1,2.....12, such that the points 1 and
11, 2 and 10, 3 and 9 etc lie on same vertical line.
• Mark the points A,B and C such that AB = BC = 30 mm. (Pitch of the helix)
• Divide AB into the same number (12) of equal parts as there are similar divisions in the circle.
• Draw horizontal lines from 0, 1',2'..... etc to intersect with the projections from 1,2,3 etc at points P , P , P ......
3
1
2
P .
12
• Join the points P , P etc with a smooth curve and form helix.
1
2
• Repeat the above procedure in portion BC and complete the helix for two revolutions.
Exercise 2.15
Construct a helical spring of 10 mm square. Cross-section has an outside dia of 60 mm and pitch 30 mm. Draw
two pitches of the spring. (Fig 4)

Fig 4

• To draw the spring with one pitch we have to draw four helixes.
• Helixes starting from A is to be drawn using procedure of the previous exercise with outside diameter 60 mm.
For helix 'D' reproduce same thing at distance 10 mm above helix A (thickness of spring 10 mm).
• Follow the above said procedure complete two helixes B&C with inside diameter 40 mm.
• Repeat four more curves and complete the two pitches of the spring.
Exercise 2.16

On a cylindrical rod of dia 80 mm a square helical groove of depth 12 mm is cut forming square thread. Assuming
the pitch equal to 24 mm, draw 2 complete turns of the thread. Find the helix angle. Assume width/thickness of
thread = depth of thread. (Fig 5)
Outside dia = 80 mm
Depth of thread = 12 mm
Pitch of thread = 24 mm
• Starting from ABCD&E, draw four helixes using the method followed in the previous exercises and complete
5 pitches by drawing parallel helical curves.
• Draw vertical lines such as PQ, RS, MN etc to represent the core of the all five pitches.
• Draw parallel lines EF and GH at any convenient distance.

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CITS :Engineering Drawing (Mechanical) - Exercise 2