Do’s and don’t’s for view creation and dimensioning

 

Imagine you are telling a story about how your object is to be made, and you are pointing out the various steps to the “builder”.

Remember you must be able to convey the entire build of your object without words and without causing the builder to ask you questions.

 

STEPS TO CONSIDER:

 

  1. VIEW CREATION
    1. Your first consideration needs to be the presentation of appropriate views to show all detail in solid object lines.
    2. To do this you will need not only the traditional orthographic views but will need section and/or auxiliary views to fully illustrate your model.
    3. To be meaningful all views must show hidden lines, however you will rarely dimension to a hidden view. The exception to this is section views which DO NOT have hidden lines shown. Detail Views also do not show hidden lines with a few exceptions.
    4. Because Solid Modeling gives us a free isometric view, use it to fully visualize the model. Generally you do not dimension in this view BUT if you do be sure to use “TRUE” dimensions.

                                                              i.      A TRUE dim is one that shows the true length of the object regardless of its orientation.

  1. FEATURE DIMENSIONING
    1. Each feature must be fully controlled by your dimensions. There will be at least 3 dimensions associated with each feature, generally reflecting the X, Y and Z locations/detail.
    2. Each dimension you place must be measurable.
    3. Indicate symmetry using Center Lines and dimension off these Center Lines
    4. The Center Line Symbol;    ; is added to non circular symmetry lines. (Center Line Linetype)
    5. Object lines are usually dimensioned in their true length, hence the use of auxiliary views.

                                                              i.      Chamfers are an exception to this rule and are generally dimensioned with an X,Y dim or X & Angle or Y & Angle. The hypotenuse is never dimensioned. This is a special circumstance as a general rule of thumb is that all objects are dimensioned in their true length.

  1. CIRCULAR FEATURES
    1. Add Center Points and Center Lines to all circular features.
    2. If an object is circular you MUST dimension to the Center Point.
    3. If you are dimensioning to circular objects on a view it is preferable to use a leader dimension.
    4. You must NEVER dimension to the edge of a hole. It is impossible to measure.
    5. If your have several holes on a common centerline and the same size collect them using 1 dimension statement followed by the note (X) to indicate quantity and be sure the centerline is extended to capture all Center Points of the holes. Use X, Y dimensions collectively as well.
    6. If you have made your hole features with the hole wizard you will be able to use the hole call out for the dims. This gives you a note for all info relating to the hole such as ID, Thread, C’Bore or C”sink, depth and so on. (This is great incentive to use the hole wizard to make all holes!)
  2. DIMENSION QUANTITY & QUALITY
    1. Avoid under dimensioning and over dimensioning. Each dimension can be shown only once on the entire drawing.

                                                              i.      Under dimensioning means that you are missing part of the information to create the feature shown.

                                                           ii.      Over Dimensioning means that you have too many dimensions. This is a problem because of a condition known as TOLERANCE STACK UP. This means that if you add up the sum of all tolerances on each dimension the total is larger than the tolerance allowed for the overall dimension. Thus you have created a Catch 22 situation for the builder and more importantly for yourself as your can’t reject his work as long as he falls within each tolerance.

  1. DIMENSION STYLE
    1. Dimensions are always layered with the largest outermost and the smallest inner most to eliminate crossing over of extension lines.
    2. The traditional gap between an object line and the extension line is 1/16”. Make sure you adjust your extensions lines to reflect that gap.
    3. Place dimensions in the view that best shows the feature.
    4. Place dimensions for a feature as close to each other as you can to make a complete statement about the object.
    5. Do not allow a visual conflict happen with your dimensions and dimension lines
    6. No dimensions are to reside within the object lines.
    7. Leader Lines are ALWAYS presented at an angle. Never at angles of 0, 90 ,180 or 270 degrees.
  2. HINTS:

In your application turn off the option that allows for automatic dimensioning. This forces you to think about the placement of each dimension.

Ultimately it will save you time and agony over learning about and producing excellent working drawings.