Where should X0 Y0 go on a rotary job, and which end of the blank does it land on?

What the datum means on a cylinder

In a rotary job only one of the two flat axes is still a real distance. The Orientation setting in the Job Setup form decides which:

• Along X Axis: X is travel along the cylinder, Y is the angle around it.
• Along Y Axis: Y is travel along the cylinder, X is the angle around it.

So the XY Datum Position you pick has two different meanings at once. Along the length it is a real spot on the blank that you must jog to. Around the cylinder it is only a starting angle: the near edge of the flat view is 0 degrees, the middle is 180 and the far edge is 360, which is the same line as 0.

How to choose and match it

1. In Job Setup, pick a corner or the center under XY Datum Position. The red square in the form shows where it sits. A corner is the default.
2. Prefer a datum at the chuck end of the job. Every cut then moves away from the chuck, so a wrong zero cannot drive the bit into the jaws.
3. At the machine, jog the length axis to that same spot on the blank and zero it. Corner datum: zero near that end of the blank. Center datum: zero at the middle of the blank's length.
4. Zero the rotary axis wherever you want the 0 degree line. On plain round stock the position usually does not matter. It matters when a feature must line up with something already on the blank.
5. If your controller homes the unused axis somewhere other than the job datum, the offset you need is in flat-view units (for example half the unwrapped dimension for a center home).

Pro tips

• If you change Orientation on a finished design, tick Flip Design so the artwork turns with the material.
• Keep the job Length shorter than the real blank so the datum corner is clear of the chuck (see the entry on planning chuck and tailstock clearance).
• A carving that is mirrored or will not rotate is a post-processor issue, not a datum issue (see the entry on rotary output that will not rotate).