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    By Martin Phelps


    When starting a technical drawing, in most cases the first items to be drawn are the centre lines to fix positions of components with in the drawing.

    Centre lines however can be added at any stage throughout the drawing process depending on the type of drawing being created.

    The addition of the “Centreline” command in AutoCAD 2017 it has now made it easier to add to drawings.

    The “Centerlines”command, is located in the “Dimensions” panel of the “Annotate” tab as show in Figure 1 or by typing in “Centerlines”. Note: - it’s the American spelling.

    Figure 1


    The “Centerline” tool creates centre line geometry that is associated with the selected lines or polyline, unfortunately it doesn’t currently work with arcs or polyarcs.

    Once the command has been initiated, select the first line or polyline then select the second line or polyline, a “Centerline” is now placed between the two selected lines, as shown in Figure 2.


    Figure 2


    Since the “Centerline” is associated to the two selected lines from which it was created, therefore if the original lines are stretched or moved the “Centerline” will also change. As shown in Figure 3.

    Figure 3


    Selecting the “Centerline” will display grips enabling the centre line length to be changed by stretching as shown in Figure 4.

    Figure 4


    The “Square Grip” controls the “Centerline” “Length”, and the “Triangular Grip” controls the “Centerline” “Overshoot”.


    The appearance of the “Centerlines” are controlled by a number of new system variables.

    “Centerexe” - sets the length of the “Overshoots” for “Centerlines”, or how far the “Centerline” extends passed the selected creation lines. The top example in Figure 5 has a value of 30, while the lower example has a value of 3.5 which is the default setting.

    Figure 5


    The “Overshoot” can be changed by using the “Centerexe” command, and updating the “Centerlines” by typing in “”Centerreset” and selecting the “Centerlines”, both of these commands are currently type-in.

    The “Overshoot” can also be controlled by selecting the “Centerline” and accessing the information via the “Properties” dialogue box. As shown in Figure 6, allowing different values to be set for each end.

    Figure 6


    Other system variables are:-

    “Centerlayer” - sets the layer on which centreline are created.

    “Centerltype” - sets the line type used in the creation of “Centerlines”.

    “Centerltscale” - sets the line type scale used by “Centerlines”.