Familiarization of Drawing symbols and Drawing ReadingE. Kishore

*A FEW BASIC ASPECTS TYPES OF VIEWSANGLES OF PROJECTIONSURFACE ROUGHNESS SYMBOLSDIMENSIONING & TOLERANCINGUNTOLERATED DIMENSIONS

*TYPES OF VIEWSORTHOGRAPHIC PROJECTION

SECTION

DETAIL

AUXILIARY PROJECTION

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*ANGLES OF PROJECTIONFIRST ANGLETHIRD ANGLE

*FIRST ANGLE PROJECTION

*COMMON LINETYPESBlack = object line and hatching Red = hidden line Blue = center line Magenta = phantom line or cutting plane

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*SURFACE ROUGHNESS SYMBOLSURFACE OBTAINED BY ANY PRODUCTION METHOD

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*THE UNIT OF SURFACE ROUGHNESS IS MICRONS.

*DIMENSIONING AND TOLERANCINGDimensioning specifications define the nominal, as-modeled or as-intended geometry.

Tolerancing specifications define the allowable variation for the form and possibly the size of individual features, and the allowable variation in orientation and location between features.

*PARALLEL DIMENSIONING

Parallel dimensioning consists of several dimensions originating from one projection line.

*SUPERIMPOSED RUNNING DIMENSIONINGSuperimposed running dimensioning simplifies parallel dimensions in order to reduce the space used on a drawing. The common origin for the dimension lines is indicated by a small circle at the intersection of the first dimension and the projection line. In general all other dimension lines are broken.

*CHAIN DIMENSIONINGChains of dimension should only be used if the function of the object won't be affected by the accumulation of the tolerances.

*COMBINED DIMENSIONING

A combined dimension uses both chain and parallel dimensioning.

*DIMENSIONING BY CO-ORDINATES

Two sets of superimposed running dimensions running at right angles can be used with any features which need their centre points defined, such as holes It is also possible to simplify co-ordinate dimensions by using a table to identify features and positions

*DIMENSIONING RADIIAll radial dimensions are preceded by the capital R. All dimension arrows and lines should be drawn perpendicular to the radius so that the line passes through the centre of the arc. All dimensions should only have one arrowhead which should point to the line being dimensioned. There are two methods for dimensioning radii.(a) shows a radius dimensioned with the centre of the radius located on the drawing. (b) shows how to dimension radii which do not need their centres locating.SPHERICAL DIMENSIONSThe radius of a spherical surface (i.e. the top of a drawing pin) when dimensioned should have an SR before the size to indicate the type of surface.

*DIMENSIONING HOLESWhen dimensioning holes the method of manufacture is not specified unless they necessary for the function of the product. The word hole doesn't have to be added unless it is considered necessary. The depth of the hole is usually indicated if it is isn't indicated on another view. The depth of the hole refers to the depth of the cylindrical portion of the hole and not the bit of the hole caused by the tip of the drill.

*DIMENSIONING CIRCLESAll dimensions of circles are proceeded by this symbol phi . There are several conventions used for dimensioning circles:(a) shows two common methods of dimensioning a circle. One method dimensions the circle between two lines projected from two diametrically opposite points. The second method dimensions the circle internally.(b) is used when the circle is too small for the dimension to be easily read if it was placed inside the circle. A leader line is used to display the dimension.(c) the final method is to dimension the circle from outside the circle using an arrow which points directly towards the centre of the circle.The first method using projection lines is the least used method. But the choice is up to you as to which you use.

* UNILATERAL TOLERANCE is a tolerance in which variation is permitted only in one direction from the specified basic dimension. e.g. 50 -0.00/+0.05,50 -0.02/-0.06, 50 +0.02/ 0.06,50 -0.00/-0.05

BILATERAL TOLERANCE is a tolerance in which variation is permitted in both directions from the specified basic dimensione.g. 50 -0.02 / +0.02

*TOLERANCE ON UNTOLERATED LINEAR DIMENSIONS Medium class of deviation is applicable , if the same is not mentioned on drawings and specifications.REF: HY0230261 & AA0230208

*TOLERANCE ON UNTOLERATED ANGULAR DIMENSIONS

UNDERSTANDINGGEOMETRICAL TOLERANCES

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STRAIGHTNESS0.10

STRAIGHTNESSTHE AXIS OF THE CYLINDER TO WHICH THE TOLERANCE FRAME IS CONNECTED SHALL BE CONTAINED IN A CYLINDRICAL ZONE OF DIAMETER 0.10.

FLATNESSIN FLATNESS, A PART SURFACE IS COMPARED TO A PERFECTLY FLAT SURFACE

FLATNESSTHE SURFACE SHALL BE CONTAINED BETWEEN TWO PARALLEL PERFECT PLANES 0.10 APART

CIRCULARITYTHIS IS A TWO DIMENSIONAL FORM CONTROLIT IS DETERMINED THAT WHETHER EACH POINT OF THE CIRCLE OF ACTUAL JOB FALLS WITHIN TWO CONCENTRIC CIRCLES THE TOLERANCE APART.

CIRCULARITY

CIRCULARITY

CIRCULARITYSINCE THE CIRCULARITY IS A TWO DIMENSIONAL FEATURE, A COMPONENT HAVING A BOW, BEND, HOUR-GLASS STRUCTURE EVEN A STACK OF COINS MAY FULFIL THE CIRCULARITY REQUIREMENTS

CIRCULARITY

CYLINDRICITYTHIS IS A THREE DIMENSIONAL FORM CONTROLIT CONTROLS CIRCULARITY, STRAIGHT-NESS AND TAPER OF THE SURFACE

CYLINDRICITY

CYLINDRICITYTHE CONTROL FRAME ARE TWO CO-AXIAL CYLINDRICAL SURFACES , THE RADIAL GAP BETWEEN WHICH EQUALS THE TOLERANCE.

THE SURFACE OF ACTUAL CYLINDER MUST LIE WITHIN THESE TWO CYLINDERS

CYLINDRICITY

TOLERANCE OF PROFILE

PROFILE OF LINE

PROFILE OF LINE 0.20

PROFILE OF SURFACECONTROL SURFACES

PROFILE OF SURFACETHUS A SHAPE LIKE ABOVE WILL BE ACCEPTED IF IT FALLS WITHIN THE TWO CONTROLLING SURFACES

*SPECIFYING PARALLELISM FOR AN AXIS

*SPECIFYING PARALLELEISM FOR A PLANE SURFACE AND AN AXIS

*SPECIFYING PERPENDICULARITY FOR A PLANE SURFACE

*SPECIFYING ANGULARITY FOR A PLANE SURFACE AND AN AXIS

*SPECIFYING CIRCULAR RUNOUT RELATIVE TO A DATUM DIAMETER

*SPECIFYING TOTAL RUNOUT RELATIVE TO A DATUM DIAMETER

*OTHER SYMBOLS IN DRAWINGS

Maximum Material Condition (MMC) - is that condition of a part feature wherein it contains the maximum amount ofmaterial within the stated limits of size. That is: minimum hole size and maximum shaft size.

Least Material Condition (LMC) - implies that condition of a part feature of size wherein it contains the least (minimum) amount of material, examples, largest hole size and smallest shaft size. It is opposite to maximum material condition.

Regardless Of Feature Size (RFS) - the condition where the tolerance of form, runout or location must be met irrespective of where the feature lies within its size tolerance.

Projected Tolerance Zone - applies to a hole in which a pin, stud, screw, etc., is to be inserted. It controls the perpendicularity of the hole to the extent of the projection from the hole and as it relates to the mating part clearance. The projected tolerance zone extends above the surface of the part to the functional length of the pin, stud, and screw relative to its assembly with the mating part.

Free State Variations - is a term used to describe distortion of a part after removal of forces applied during manufacture.

Diameter - indicates a circular feature when used on the field of a drawing or indicates that the tolerance is diametrical when used in a feature control frame.

*OTHER SYMBOLS IN DRAWINGS

Basic Dimension - used to describe the exact size, profile, orientation or location of a feature. A basic dimension is always associated with a feature control frame or datum target. (Theoretically exact dimension in ISO)

Reference Dimension - a dimension usually without tolerance, used for information purposes only. It does not govern production or inspection operations. (Auxiliary dimension in ISO)

Datum Feature - is the actual component feature used to establish a datum.

Dimension Origin -Signifies that the dimension originates from the plane established by the shorter surface and dimensional limits apply to the other surface.

Feature Control Frame - is a rectangular box containing the geometric characteristics symbol, andthe form, runout or location tolerance. If necessary, datum references and modifiers applicable to the feature or the datums are also contained in the box.

*OTHER SYMBOLS IN DRAWINGS

Conical Taper -is used to indicate taper for conical tapers. This symbol is always shown with the vertical leg to the left.

Slope -is used to indicate slope for flat tapers. This symbol is always shown with the vertical leg to the left.

Counterbore/Spotface -is used to indicate a counterbore or a spotface. The symbol precedes the dimension of the counterbore or spotface, with no space

Countersink -is used to indicate a countersink. The symbol precedes the dimensions of the countersink with no space.

Depth/Deep -is used to indicate that a dimension applies to the depth of a feature. This symbol precedes the depth value with no space in between.

Square -is used to indicate that a single dimension applies to a square shape. The symbol precedes the dimension with no space between.

Number of Places -the X is used along with a value to indicate the number of times a dimension or feature is repeated on the drawing.

Arc Length -indicating that a dimension is an arc length measured on a curved outline. The symbol is placed above the dimension.

Radius -creates a zone defined by two arcs (the minimum and maximum radii). The part surface must lie within this zone.

*OTHER DRAWING SYMBOLS

Spherical Radius -precedes the value of a dimension or tolerance.

Spherical Diameter -shall precede the tolerance value where the specified tolerance value represents spherical zone. Also, a positional tolerance may be used to control the location of a spherical feature relative to other features of a part. The symbol for spherical diameter precedes the size dimension of the feature and the positional tolerance value, to indicate a spherical tolerance zone.

Controlled Radius -creates a tolerance zone defined by two arcs (the minimum and maximum radii) that are tangent to the adjacent surfaces. Where a controlled radius is specified, the part contour within the crescent-shaped tolerance zone must be a fair curve without flats or reversals. Additionally, radii taken at all points on the part contour shall neither be smaller than the specified minimum limit nor larger than the maximum limit.

Datum Target - is a specified point, line, or area on a part that is used to establish the Datum Reference Plane for manufacturing and inspection operations.

Target Point -indicates where the datum target point is dimensionally located on the direct view of the surface.