Now I turned my attention to the second cage. I measured from the top hole in the cage to the underside of the top tube then cut the zip ties. That measurement was then marked on the frame with a scribe and a second one 64mm below. The centre of the tube was then scribe at these points "by eye" but I could have been more scientific if I hadnt just got carried away! I then centre punched these using an automatic center punch which didnt need a hammer swinging around inside the frame.