DIMENSIONS IN MECHANICAL ENGINEERING DRAWINGS
In order for the drawings to be dimensioned so that evryone can understand them, we need to follow standards that all people in the world must follow. Standards are created by these organizations:
Dimensions are represented on a drawing using on of the two systems, unidirectional or aligned.
1. Dimensions should NOT be duplicated or the same information given in two different ways.
2. No unnecessary dimensions should be used. Only those needed to produce or inspect the part.
Units of Measure:
TYPES OF DIMENSIONING
Standard Linear Dimensioning: Dimensioning from feature to feature is known as Chain Dimensioning. It is commonly used and easy to lay out. It does have possible consequences in the manufacturing of a part. Tolerances can accumulate, making the end product larger or smaller than expected. The accuracy of the final product is determined by the dimensions on the drawing. If all the dimensions originate from a common corner of the part, the object will be accurate. This is refered to as Datum Dimensioning. Datum insure the tolerance or errors in manufacturing do not accumulate.
Basic linear dimensions:
Sheet Metal dimensions:
Chain Dimensioning: Dimensioning from feature to feature is known as Chain Dimensioning. It is commonly used and easy to lay out. It does have possible consequences in the manufacturing of a part. Tolerances can accumulate, making the end product larger or smaller than expected. In a chain of dimensions, dimension the width and height of the subject/part in the front view. The front view is preferred because it is supposed to provide the most information about an object’s geometry
Dimensioning Angles: Angled surface may be dimensioned using coordinate method to specify the two location distances of the angle. Angle surfaces may also be dimensioned using the angular method by specifying on location distance and the angle.
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 ar dimensioned with a leader to identify the diameter.
Dimensioning Curved Features and Arcs: The arrow can be inside for small arcs. Small arcs do not need center marks. Arrow can be outside. Large arcs use center marks. Use a capital "R" for dimensioning arcs. A center line is a dark line composed of alternate long and short dashes, and is used to represent the axes of symetrical parts or to denote centers. Do not create a gap when the centerline crosses the part outline. A centerline must end with a long dash.
Reference Dimensions: Designates more than one of the same feature. In this case, it is identifying there are two identical radius.
Chamfers: There are two options for external chamfer for 45 degree chamfer and basic dimension for angles other than 45 degrees and internal chamfers.
Fillets and Rounds: Large arcs use center marks. Small arcs do not need center marks. Arrow can be outside the arc. Use capital "R" for dimensioning the arcs.
Conical Tapers — Slot Dimensioning — Dimensioning Radial Patterns — Keyways and Keyseat...to be continous.
Reading a Hole Note:
Reading Thread Note:
G E O M E T R I C D I M E N S I O N & T O L E R A N C E
Inserting a Geometric Dimension & Tolerance in Model/Part:
Creating Datum References in Model: Model Select a surface/edge/