Since we can view the hollowing out as a complementary operation to the extrusion, SolidWorks is made to be driven the same way for both operations. So, to make a hole in an existing body (constructed for instance with an extrusion), we need to make another sketch “somewhere”, for instance on one of its faces (but we could make it also on a plane which cuts the object, so we could start from the “inside”). Then we press the ‘Extruded cut’ button from the middle row (once ‘Features’ is on), and we obtain our hole. This is what we want to obtain:
So we start again sketching, on the top part of the cylinder. We want to sketch a circle, and we want it centered in the same center as the outer circle. This is easy, because again SolidWorks helps us, by automatically highlighting the center if we hover above the circular edge, once we have started the sketch.
So we start as before: we select the top face (it becomes light blue), we go into ‘Sketch’, click on the ‘Sketch’ button, pick the Circle shape to sketch and go hover above the edge — we then see the center appear.
We go towards it (it is ok that the edge is no longer orange, the highlighting of the center patiently remains on, so we can find it and click on it). We thus start drawing the circle outwards, and click to finalize it.
Then we go click on the ‘Features’ menu entry and on the ‘Extruded Cut’ button
Right after clicking we see the yellow preview of the cut and we can again adjust its depth with the arrow:
We can also adjust the depth by typing the exact number we wish to have in the left dialog box. Finally, as with everything else, we can rotate the image while we are adjusting the depth of the cut, to better see what we are doing. When we are happy, we finalize the cut.