Lecture 1- Dimensioning

  • Working drawing- drawing from which a part can be produced
  • Must be a complete set of instructions so the part can produced without provided further information to the fabricator
  • Consists of:
  • Views necessary to explain the shape
  • Dimensions needed for manufacture
  • Required specifications (such as material and finish)
  • Additional information (such as drawing #, date, part name(s), drafter’s name, etc.)
  • Detail drawing- information/drawing of individual part(s); shown on separate sheets or grouped on one sheet
  • Assembly drawing-information on how parts will be assembled
  • Dimension- a numerical value expressed in appropriate units of measure and use to define the size, location, orientation, form, or other geometric characteristic of a part
  • Given on drawings by extension lines, dimension lines, arrowheads, figures, notes, and symbols

Basic Rules for Dimensioning

  • Dimension in the view where the feature appears true size and shape (i.e. the view that BEST shows the characteristic contour or shape of the object
  • Place dimension between views when possible
  • Place the dimension line for the shortest length, width, or height nearest to the object- therefore, longest dimension will be furthest from the drawing
  • Only one system of dimensions (unidirectional or aligned) should be used on a drawing
  • Dimensions should not be repeated in other views
  • Dimensions should be completed so there is full definition of each part feature
  • Each dimension should have a tolerance (except dimensions specifically identified as reference, maximum, minimum, or stock size)

Reference Dimensions: dimension shown for information only- reference dimensions are enclosed in parentheses

DIMENSIONING METHODS

  • Choice of dimensioning methods will depend on how the part will be produced or whether the part is intended for mass production or unit production

Rectangular Coordinate Dimensioning: dimensions for location, size, and location are placed parallel or perpendicular to reference axes or datum planes that are perpendicular to one another

Chain Dimensioning: places dimensions in a line from one feature to the next

  • Use DIMCONTINUE
  • May result in an undesirable accumulation of tolerances

Datum or Baseline Dimensioning: dimensions originate from a common point or line

  • In AutoCAD, use DIMBASELINE or QDIM

Arrowless dimensioning

  • AutoCAD refers to arrowless dimensioning as ordinate dimensioning
  • Use QDIM or DIMORDINATE

Tabular Dimensioning: A form of arrowless dimensioning in which dimensions to features are shown on a table

Chart Dimensioning: a unidirectional, aligned, arrowless, or tabular dimensioned drawing used when dimensions change values

Polar Coordinate Dimensioning: method of indicating the position of a point, line, or surface by means of a linear dimension and angle (other than 90 degrees)

  • commonly used in circular planes or circular configurations of features

Chordal Dimensioning: used for the spacing of points on the circumference of a circle relative to a datum, where manufacturing methods indicate that this method will be convenient