You can position a datum axis by selecting a cylindrical or conical face on the model. ABAQUS/CAE creates a datum axis that lies along the axis of the face.
To create a datum axis along the axis of a cylinder:
From the main menu bar, select Tools
Datum.
The Create Datum dialog box appears. The dialog box outlines the types of datum geometry you can create.
ABAQUS/CAE displays prompts in the prompt area to guide you through the procedure.
Tip:
You can also create a datum axis using the 
tool, located in the module toolbox. For a diagram of the datum tools in the toolbox, see “Using the Datum toolset,” Section 40.2.
From the list of types at the top of the dialog box, choose Axis.
The Method list indicates the methods you can use to create a datum axis.
From the Method list, select Axis of cylinder and click OK.
From the part or assembly in the current viewport, select a a cylindrical or conical face.
The datum axis appears. You cannot modify a datum axis created with this method; you must delete the old axis and create a new one.
