Applying Ordinate Dimensions

In mechanical drafting, ordinate dimensions are used to maintain the accuracy of machined parts by establishing an origin on the part. All major dimensions are described as X coordinates or Y coordinates of that origin. The origin is usually an easily locatable feature of the part, such as a machined bore or two machined surfaces.

Figure 9.24 shows a typical application of ordinate dimensions. In the lower-left corner, note the two dimensions whose leaders are jogged. Also note the origin location in the upper-right corner.

Figure 9.24: A drawing using ordinate dimensions

To use AutoCAD's Ordinate Dimension command, perform the following steps:

1. Click Tools   UCS   Origin or type UCS Or .

2. At the Specify new origin point <0,0,0>: prompt, click the exact location of the origin of your part.

3. Toggle the Ortho mode on.

4. Click the Ordinate Dimension tool on the Dimension toolbar. You can also enter Dor to start the ordinate dimension.

5. At the Specify feature location: prompt, click the item you want to dimension.

   Tip  

   The direction of the leader determines whether the dimension will be of the Xdatum or the Ydatum.

6. At the Specify leader endpoint or [Xdatum/Ydatum/Mtext/Text/Angle]: prompt, indicate the length and direction of the leader. Do this by positioning the rubber-banding leader perpendicular to the coordinate direction you want to dimension and then clicking that point.

In steps 1 and 2, you used the UCS feature to establish a second origin in the drawing. The Ordinate Dimension tool then uses that origin to determine the ordinate dimensions. You will get a chance to work with the UCS feature in Chapter 16.

You might have noticed options in the Command window for the Ordinate Dimension tool. The Xdatum and Ydatum options force the dimension to be of the X or Y coordinate no matter what direction the leader takes. The MText option opens the Multiline Text Editor, enabling you to append or replace the ordinate dimension text. The Text option lets you enter replacement text directly through the Command window.

Tip  

As with all other dimensions, you can use grips to adjust the location of ordinate dimensions.

If you turn Ortho mode off, the dimension leader will be drawn with a jog to maintain the orthogonal (look back at Figure 9.24).