Dimensioning Standards

Dimensioning Standards In order for the drawings to be dimensioned so that all people can understand them, we need to follow standards that every company in the world must follow. Standards are created by these organizations: ANSI ISO MIL DOD CEN DIN JIS

Standards Institutions ANSI - American National Standards Institute. This institute creates the engineering standards for North America. ISO - International Organization for Standardization. This is a worldwide organization that creates engineering standards with approximately 100 participating countries.

Standards Institutions The United States military has two organizations that develop standards. DOD - Department Of Defense MIL - Military Standard

Standards Institutions DIN - Deutsches Institut für Normung. The German Standards Institute created many standards used worldwide, including the standards for camera film. JIS - Japanese Industrial Standard. Created after WWII for Japanese standards. CEN - European Standards Organization.

Dimension Components Dimension Line Dimension Text Arrow Head Extension Lines

Dimension Text Guidelines If the dimension text will not fit between the extension lines, it may be placed outside them

Dimension Text Guidelines Dimension text is placed in the middle of the line both horizontally and vertically

Dimensioning Methods Dimensions are represented on a drawing using one of two systems, unidirectional or aligned. The unidirectional method means all dimensions are read in the same direction. The aligned method means the dimensions are read in alignment with the dimension lines or side of the part, some read horizontally and others read vertically.

Dimensioning Methods Aligned Unidirectional Dimensions are placed so that they can be read from the bottom of the drawing sheet. This method is commonly used in mechanical drafting. Aligned Dimensions are placed so the horizontal dimensions can be read from the bottom of the drawing sheet and the vertical dimensions can be read from the right side of the drawing sheet. This method is commonly used in architectural and structural drafting.

Classification of Dimensions Size. Dimensions are used to identify the specific size of a feature on an object. Location. Dimensions are used to identify the physical proximity of a feature to another feature within an object. Size dimension Location dimension Location dimension Size dimension

Linear Dimensioning Chain Dimensioning Dimensioning from feature to feature Common dimensioning technique

Chain Dimensioning Examples Presentation Name Course Name Unit # – Lesson #.# – Lesson Name Chain Dimensioning Examples METHOD 1 METHOD 2 Dimension from feature to feature across entire part Manufacturing inaccuracies can accumulate Dimension from feature to feature except omit one partial dimension in the chain Dimension overall length/width/height to limit manufacturing inaccuracies Preferable chain dimensioning method It is impossible to manufacture a part to an exact dimension. If a part is measured precisely enough, the part configuration will deviate from the specified dimensions. Typically a small amount of deviation from the specified dimension is allowed, but the error can add up in a chain of dimensions compounding the error and resulting in a part that is much smaller or larger than intended. Therefore, specifying the overall dimension (with its small allowable error in that one dimension) will reduce the deviation of the overall part size. We will talk about tolerances, the allowed deviation of a dimension on a manufactured part from the specified dimension, later in this unit. For now, when chain dimensioning, use the preferred method (Method 2) when possible.

Datum Dimensioning Datum Dimensioning Dimensioning from a single point of origin called a DATUM Reduces dimensional deviations in manufactured parts because each size/location dimension is referenced to a single point

Datum Dimensioning

Dimensioning Symbols Presentation Name Course Name Unit # – Lesson #.# – Lesson Name Dimensioning Symbols Some common dimensioning symbols.

Dimensioning Angles Angled surface may be dimensioned using coordinate method to specify the two location distances of the angle. Angled surfaces may also be dimensioned using the angular method by specifying one location for distance and the angle. Coordinate Method Angular Method

Dimensioning Chamfers Presentation Name Course Name Unit # – Lesson #.# – Lesson Name Dimensioning Chamfers Internal Chamfers Two options for 45 degree external chamfers Chamfers are used on outside edges to avoid sharp corners for safety and handling. External chamfers other than 45 degrees

Dimensioning Arcs and Circles Arcs and circles are dimensioned in views that show the arc or circle. Arcs are dimensioned with a leader to identify the radius; in some cases, a center mark is included. Circles should have a center mark and are dimensioned with a leader to identify the diameter.

Dimensioning Arcs Use a capital R to indicate radius Arrows can be inside or outside for small arcs. Small arcs do not need center marks. Large arcs need a center mark

Presentation Name Course Name Unit # – Lesson #.# – Lesson Name Fillets and Rounds Fillet. An inside radius between two intersecting planes Round. An outside radius applied to corners Fillet Round A round is used to avoid sharp edges for safety and handling. A fillet is used to provide strength at inside corners to avoid fracture. In addition fillets and rounds (as opposed to sharp corners) can make it easier to remove molded parts from molds. Identify which arcs are fillets and which are rounds.

Dimensioning Circles Holes should use hole notes Full circles should be dimensioned using the diameter This hole note specifies a hole with a 0.50 diameter and 1.00 deep

Cylindrical parts may be dimensioned in this manner Dimensioning Circles Cylindrical parts may be dimensioned in this manner Note that the diameter symbol is used so that the dimension is not assumed to be linear

Dimensioning Splines and Curves Points are placed along the contour of splines and dimensioned from a datum. DATUM

Dimensioning Splines and Curves Presentation Name Course Name Unit # – Lesson #.# – Lesson Name Dimensioning Splines and Curves This section view provides coordinate dimensions for the curvature of the windshield of the Automoblox T9 truck. We refer to these dimensions as coordinate dimensions because the horizontal and vertical distances from a given point, the datum (or origin), are given for each identified point along the curve. DATUM

Reference Dimensions “X” indicates the number of places (or occurrences) 2 X indicates that there are two identical holes

Dimensioning Radial Patterns Angles and radius values are used to locate the center of radially patterned features