• The active part and workplane are selected by default. You may want to create a new part, or work on a different part. Don't forget to change the part and/or workplane when you start a machining command, if necessary.

• Your changes aren't complete until you click OK. Although you can see the machining operation as a preview in the viewport, your changes aren't saved unless you click the green checkmark.

• All profiles on a workplane are machined. If you use the same workplane for more than one operation, you need to delete unwanted profiles before you begin the next operation.

• Hidden parts can be machined. If it looks like the machine operation isn't doing anything, the part probably isn't visible. Check the parts in the structure browser to make sure your part is visible. A part is hidden when it is unchecked.