If you’re looking to extrude/cut a simple feature through your part, the following steps should do the trick.
In the model workspace create an axis through the center of the revolved object. Once you’ve created the axis, create a work plane on the axis and select which plane (XY/XZ/YZ) you want to apply the work plane to. Once you’ve created the work plane you can select it and select the “sketch” option to make it a sketch plane. Now sketch whatever profile you want to cut out of the object, finish the sketch, and perform an extrude/cut on the part model.
Note: If you leave the sketch plane on the axis of the revolved part you can use the “slice graphics” option (right mouse click in the sketch window and select “slice graphics”) for easier sketching of the feature.
If you don’t want to create a feature that is cut all the way through the object you will have to offset the work plane by dragging it away from the work axis and entering an offset distance.
Try this out. If it doesn’t work, PM me and I can give you more detailed directions.