machine drawing mec-304

Machine DrawingMEC-304

Dr. Shankar SehgalAsst. Professor in Mech. Engg.

UIET, Panjab University, Chandigarh

Standard Abbreviations

Tolerances and Fits

Tolerancing individual dimensions

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

Any special machining characteristics are mentioned on the extra horizontal line

Milled

Surface finish

Actual profile

Reference profile

Datum profile Mean profile

Peak-to-valley height

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.


• 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.


• 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 edge2. Surface guage3. Optical flat4. Tool maker’s microscope5. Profilometer6. Profilograph7. 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

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 line

• 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.


• 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.


continuous thick line

continuous thin line


dotted line

Schematic representation of threaded parts - V-threads

Schematic representation of threaded parts - Square-threads

Bolted joint

Hexagonal nut

Method of drawing hexagonal nut1. 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 R1 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 R2 geometrically.

Hexagonal headed bolt

Hexagonal headed bolt with nut and washer

Square nut

Square headed bolt

Stud bolt or stud

Screws

Lock nut

Locking by split pin

Locking by castle nut

Wile’s lock nut

Locking by set screw

Pipe fittings

Cotter Joint

Knuckle Joint

Muff coupling

Flange coupling

Footstep bearing

Front view of footstep bearing

Top view of footstep bearing

Footstep bearing

Plummer block

Front view of plummer block

Top view of plummer block

Plummer block

Screw jack

I.C. engine piston

I.C. engine connecting rod

Lathe tail stock

machine drawing mec-304

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