How to configure rotary axes

For the CAM-POST developer, it can sometimes be confusing to configure the rotary axes kinematics when a machine has two or more rotary axes of the same type, e.g., two heads or two tables. Rotary axes must be configured correctly to ensure that the desired output is achieved.

To avoid any confusion, you must select the order in which the machine tool builder assembled the two axes. The following selections allow you to choose the “highest” (or primary) rotary head, followed by the “next” (or secondary) rotary axis, as well as the lowest rotary axis if one exists. A similar panel appears when defining rotary tables, defining their order from bottom to top.

Usually the highest (primary) head is easy to choose, but sometimes the secondary head is more of a problem. If the primary head is a C axis, then which axis (A or B) is the secondary? This choice is easy when you have access to the machine tool. Just set the primary axis (C axis in this case) to zero. The secondary axis will then show what its axis nomenclature (A or B) is. If it rotates about the X axis, then this is an A axis, and it if rotates about the Y axis, then it is a B axis.

This step is critical in configuring a post for CAM-POST because the kinematic chain is constructed using the rules set by the ISO standards, where A rotates about the X axis, B about the Y axis, and C about the Z axis. Sometimes the machine tool builder does not label the axis according to the ISO standards, in which case after you have configured the axes according to the ISO rules, you can then name the axes to comply with the names the builder used.

Sometimes the axes themselves do not conform to ISO rules, in which case you can define a custom orientation of a rotary axis (e.g., one with 45° orientation) and/or define an axis whose positive sense of rotation is opposite that of the Standard right-hand-rule.

Finally, CAM-POST expects that the tool will be parallel to the Z axis of the machine, but when this is not the case, you can define a custom orientation of the spindle face as well as the spindle “zero orient” direction.

Benefit to User
CAM-POST advanced kinematics and Questionnaire features make it easy to define rotary axes and spindle heads that exactly match the CNC machine.

For more information or comments, please do not hesitate to contact Phil at