Engg engg academia_commonsubjects_drawingunit-i

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  • 1. Engineering Drawing I Year B.Tech By NN..SSRRIINNIIVVAASSAA RREEDDDDYY..,, M.Tech. Sr. Assistant Professor Department of Mechanical Engineering Vardhaman College of Engineering

2. SCALES Unit-I Representative Fraction - The Ratio of length of the drawing to the actual length of the object represented is called Representative Fraction (R.F). - R.F. is less than unity is drawn on reduced scale, if greater than unity enlarging scale, if equal to one full scale. Scales on Drawing Sheet i) Representative fraction of the scale. ii) The units in which it must present i.e. (mm, cm, dm, inch, feet). iii) The maximum length which it must show (original length). Types of Scales: 1) Plane Scale - It consists of a line divided into suitable no. of equal parts or units. The 1st of which is subdivided into smaller parts. - Plane scale represent either two unit (or) a unit and it's subdivision. Procedure - The zero should be placed at the end of 1st main division between the unit and it's subdivision. - From the zero mark unit's should be numbered to the right and subdivision to the left. - The names of the units and the subdivisions should be stated clearly below or at the respective ends. - The name of the scale i.e. 1:10 or it's representative fraction should be mentioned below the scale. Problem-1 Construct a scale of 1:4 to show cm and long enough to measure upto 5dm and show distance of 3.7 dm on scale. Procedure 1. Determine R.F of the scale, here it is 1/4. 2. Determine length of the scale = R.F max.length = 1/4 5dm = 12.5 cm 3. Draw a line of 12.5 cm long and divided it into 5 equal division each representing 1 dm. 4. Mark O at the end of 1st division and 1, 2, 3 & 4 at the end of the each of each subsequent division to it's right. 5. Divide the 1st division into 10 equal parts each representing 1 cm. 6. Mark cm to the left of zero and decimeter to the right corner. 7. To distinguish the division clearly show the scale as a rectangle of small width (about 3mm). 8. Draw the division line showing decimeter throughout the width of the scale. 9. Draw the lines for subdivision slightly shorter as shown in figure. 10. Draw thick and dark horizontal lines in the middle of all alternative division and subdivision. 3. 2. Diagonal Scale - It is used when every minute distances such as 0.1 mm etc are to be accurately measured or when measurements are required in 3 units. Ex: DM, CM, MM, Yard, Foot and Inches. - Small divisions of short are obtained by the principle of diagonal division. Principle of Diagonal Scale - To obtain division of a given short line AB in multiples of 1/10 of it's length. Ex: 0.1 of AB, 0.2 of AB etc. Procedure 1. At one end say B draw a line perpendicular to AB and along it a step of 10 equal divisions of any length (but uniform) starting from B and ending at C. 2. No.of divisions points 9, 8, 7, 6 upto C. Join A with C. 3. Draw lines parallel to AB and cutting AC at 1', 2' etc. It is evident that le 1'1C, 2'2C, 3'3C soon. ABC are similar so 1'1 = 0.1 AB, 2'2 = 0.2 AB etc. Problem Construct a diagonal scale of 3:200 i.e. showing meters, decimeter and centimeter and to measure a distance upto 6m. Show a distance of 4m, 5dm, 6cm. Procedure 1. Draw a line AB = 9cm and divide it into 6 equal parts each part will show a meter. 2. Divide the 1st part i.e. left side of O in 10 equal divisions each showing dm or 0.1m. 3. At a draw a perpendicular and set off along it 10 equal divisions of any length ending at D. 4. Complete the rectangle ABCD, draw perpendicular at meter division 0, 1, 2, 3 and 4. 5. Draw horizontal lines through the division points on AD. 6. Join D with the end of 1st division along AO i.e. AO at point 9. 7. To the remaining points drawn parallel to D9. 10 equal division AD ; Draw line D to AO (9th part) 2 1:66 3 4. 8. In OFE, FE represents 1DM or 0.1M each H.L below FE progressively diminishes in length by 0.1 FE. Thus, next line below FE = 0.9 FE and represents 0.9 DM or 0.09M or 9CM. Geometrical Construction 1. Bisecting a line. 2. To draw perpendiculars. 3. To draw parallel lines. 4. To divide a line. 5. To bisect an angle. 6. To trisect an angle. 7. To find centre of an arc. 8. To construct equilateral le. 9. To construct squares. 10. To construct regular polygon. 11. Special method for drawing regular polygon. 12. Regular polygon inscribed in circles. 13. To draw regular figures using T-square and set square. 14. To draw tangents. 15. To find length of arcs. 16. Circles and lines in contact. 17. Inscribed circles. 1. Bisecting a line (line length = 10 cm) Procedure - Let AB be the given line with center A and radius greater than half of AB draw an arcs on both sides of AB. - With centre and the same radius draw arcs intersecting the previous arcs at C and D. Draw a line joining C and D, cutting A and B at E. Then, - Further CD bisects AB at right angles. - AB is thick line and also CD is thick but lighter than AB. 1 AE EB AB 2 = = Arcs must be lighter 5. 2. To bisect a given Arc (R = 5cm) - Let AB be the given arc with centre A and radius greater D half of AB draw arcs on either side of AB. - Centre B with same radius draw arcs intersecting previous arcs at C and D. Draw a line joining C and D upto O and cutting AB at E then 3. To draw perpendicular lines (10 cm, P = 4 cm from B) - To draw a perpendicular to a given line from a point within it. Procedure - Case-I - Let the point is near middle of the line. Let AB be the given line and P the point in it. - With P as centre and any convenient radius draw an arc cutting AB at C and D. - With any radius r2 > r1 and centre C and D draw arcs intersecting each other at O. Draw a line joining P and O, then PO is required perpendicular. Case-II (AB = 10 cm, P is at 2 cm) - When the point is near or end of the line. - Let AB be the given line and P the point in it. Method-I 1. With any point O as centre and radius equal to OP draw an arc greater than semicircle cutting AB at C. 2. Draw a line joining C and O and produce it to cut the arc at Q. Draw a line joining P and Q. then PQ is required perpendicular. 1 AE EB AB 2 = = AB and PQ are thick lines AB is thick line OP is thick line centre of arc and arcs thick 6. Method-II - With P as center and any convenient radius draw an arc cutting AB at C. - With the same radius cut the arc in two equal divisions CD and DE. - With the same radius with centre D and E draw an arcs intersecting each other at Q. Draw a line joining P and Q then PQ is required perpendicular. Case-III - To draw a perpendicular line to a point outside it (nearer to midpoint) Procedure (10cm, above AB 4cm) - Let AB be the given line and P is the point. - With centre P and any convenient radius draw an arc cutting AB at C and D. - With any radius greater than 1/2 CD with centre C and D draw arcs intersecting each other at E. Draw a line joining P and E and cutting AB at Q. PQ is required perpendicular. Case-IV When the point nearer to end then centre of line and outside of AB. - With centre A and radius equal to AB draw an arc EF cutting AB (or) AB produced at C. - With centre C and radius equal to CP draw an arc cutting EF at D. Draw a line joining P and D and intersecting AB at Q then PQ is required perpendicular. 7. 4. To draw parallel lines - To draw a line through a given point parallel to a given straight line AB = 10cm parallel point = 4cm above AB. Procedure - Let AB be the given and P is the given point with centre P and any convenient radius draw an arc CD cutting AB at E. - With centre E with same radius draw an arc cutting AB at F. With centre E and radius equal to FP draw an arc to CD at Q. - Draw a straight line through P and Q then this is the required line. Case-II - To draw a line parallel to at a distance from a given. Procedure Let AB is the given line and r is given distance, mark P, Q, S on AB of convenient distance. - With P, Q and S as centre and radius r draw arcs on same side of AB. Draw the line CD just touching the 3 arcs CD is required line parallel to AB. Rule-1 - For the force components is any quadrant away from origin and making angle (making an angle with either of the axis). - The force makes an angle with either x-axis or y-axis, corresponding axis component is always cos and the opposite axis is sin. Apply the sin value corresponding quadrant. 8. Rule-2 - Force component towards horizon making an angle . I-quadrant - Change the position into opposite quadrant and the angle with the same axis, then apply rule-1. II-Quadrant III-Quadrant 9. IV-Quadrant Centre of gravity 1. For a line or uniform rod - mid point. 2. Circle - centre 3. Semi circle - 4r/3 from the base. 4. Quadrant - 4r/3 from the centre. 5. 11gm, square, rectangle - intersection of diagonals. 6. le - h/3 from base and intersection of medians. 5. To divide a line - Let AB be the given line to be divided into 7 equal parts (AB = 7cm) 1. Draw a line AC of any length inclined at some convenient angle to AB but less than 90. 2. From A and along AC cut off with a divider 7 equal divisions of any convenient length. Draw a line joining B and 7th division on AC. 3. With the aid of two set square's draw lines through 1, 2, 3 etc parallel to B7, intersecting AB at points 1', 2', 3' etc. Thus dividing it into 7 equal parts. 6. To divide a given straight line into unequal parts - Let AB be the given to be divided into unequal parts say 1/6, 1/5, 1/4, 1/3, 1/2 (AB = 12cm) 1. Draw a line AB of given length say 120mm. 2. Draw perpendicular AD and BC at the ends AB and complete rectangle ABCD. 3. Join diagonals AC and BD intersecting at E. From E onto AB draw perpendicular then AF = 1/2 AB. 4. Join D and F, the line DF intersect the diagonal AC at G. Drop perpendicular from G to AB then AH = 1/3 AB. 5. Join D and H intersecting diagonal AC at I, from I draw perpendicular on to AB then AJ = 1/4 AB, similarly for other fraction. 10. 7. To bisect an angle - Let ABC be the given angle with B as