In the case in hand, it might seem the logical thing to start with the center of the machine - the shaft - and work outward, completing each part as it is reached. However, if we start with the shaft, we soon find that we do not have sufficient data to complete the drawing. While the designer has given some data from which we could start, as for instance the length between bearings and the weight, we must also know the dimensions of the armature and commutator spiders before the shaft drawing can be completed; therefore, we must first work up the armature and commutator.