Machine Drawing MEC354 Shankar Sehgal UIET Panjab University

Machine Drawing MEC-354 Shankar Sehgal UIET, Panjab University, Chandigarh

Standard Abbreviations

Tolerances and Fits

Tolerances and Fits

Tolerancing individual dimensions

Fits

Shaft basis system

Hole basis system

Machining symbols

Machining symbol Any machining method may be used

Machining symbol Circle means: Material removal not permitted

Machining symbol Bar means: Material removal by machining is required

Machining symbol Milled Any special machining characteristics are mentioned on the extra horizontal line

Surface finish Reference profile Peak-to-valley height Actual profile Datum profile Mean profile

Surface finish parameters • Actual profile: – It is the profile of the actual surface obtained by finishing operation • Reference profile: – It is the profile to which the irregularities of the surface are referred to. It passes through the highest point of the actual profile.

Surface finish parameters • Datum profile: – It is the profile, parallel to the reference profile. It passes through the lowest point B of the actual profile. • Mean profile: – It is that profile, within the sampling length chosen (L), such that the sum of the material filled areas enclosed above it by the actual profile is equal to the sum of the material-void areas enclosed below it by the profile.

Surface finish parameters • Peak-to-valley height: – It is the distance from the datum profile to the reference profile. • Mean roughness index: – It is the arithmetic mean of the absolute values of the heights hi between the actual and mean profiles. It is given by,

Surface roughness number

Surface finish symbols

Measurement of surface finish 1. Straight edge 2. Surface guage 3. Optical flat 4. Tool maker’s microscope 5. Profilometer 6. Profilograph 7. Talysurf

Surface finish symbols

Welding symbols

Elementary welding symbols

Supplementary welding symbols

Combination of elementary and supplementary welding symbols

Welding symbols

Indication of edge preparation Dotted line is on LOWER side. This means that LOWER plate is to be prepared Welding symbol on continuous line (and not on dotted line). This means that weld is to be made on arrow side (and not on the other side).

Weld dimensions a = throat thickness z = leg length

Welding process designations

Screw threads

Forms of screw threads Metric screw thread

Forms of screw threads

Thread designation • M 10 x 1. 25 means – Metric thread of nominal diameter 10 mm and pitch 1. 25 mm (Fine series) • M 10 means – Metric thread of nominal diameter 10 mm and pitch 1. 5 mm (Coarse series) • SQ 40 x 10 means – SQuare thread of nominal diameter 40 mm and pitch 10 mm • ACME 40 x 8 means – ACME thread of nominal diameter 40 mm and pitch 8 mm • WORM 40 x 10 means – WORM thread of nominal diameter 40 mm and pitch 10 mm

Left hand thread Side mirror of Activa scooter

Right hand thread

Conventional representation of threads • Crests of threads are indicated by a continuous thick line and the roots, by a continuous thin line. • For hidden screw threads, the crests and roots are indicated by dotted lin • For threaded parts in section, hatching should be extended to the line defining the crest of the thread. • In the view from side, the threaded roots are represented by a • portion of a circle, drawn with a continuous thin line, of length approximately three-quarters of the circumference.

Conventional representation of threads • The limit of useful length of screw threads is represented by a continuous thick line or a dotted line, depending on its visibility. The length up to which the incomplete threads are formed beyond the useful limit, is known as a run-out. It is represented by two inclined lines.

Conventional representation of threads

Schematic representation of threaded parts - V-threads

Schematic representation of threaded parts - Square-threads

Bolted joint

Hexagonal nut

Method of drawing hexagonal nut 1. Draw the top view by drawing a circle of diameter, W and describe a regular hexagon on it, by keeping any two parallel sides of the hexagon, horizontal. 2. Project the view from the front, and the view from side, and mark the height equal to D. 3. With radius R, draw the chamfer arc 2 -1 -3 passing through the point 1 in the front face. 4. Mark points 4 and 5, lying in-line with 2 and 3. 5. Locate points 8, 9 on the top surface, by projecting from the view from above. 6. Draw the chamfers 4– 8 and 5– 9. 7. Locate points 6 and 7, lying at the middle of the outer two faces. 8. Draw circular arcs passing through the points 4, 6, 2 and 3, 7, 5, after determining the radius R 1 geometrically. 9. Project the view from the side and locate points 10, 11 and 12. 10. Mark points 13 and 14, lying at the middle of the two faces (view from the side). 11. Draw circular arcs passing through the points 10, 13, 11 and 11, 14, 12, after determining the radius R 2 geometrically.