This section is from the book "Cyclopedia Of Architecture, Carpentry, And Building", by James C. et al. Also available from Amazon: Cyclopedia Of Architecture, Carpentry And Building.
Introduction. Structural drafting may be defined as the art of making drawings of certain objects and placing thereon dimensions and other notes which when taken together will convey the necessary information for the manufacture and in some cases the erection of the structure under consideration.
In the making of these drawings great accuracy in drafting is not necessarily required. The chief requisites are that the lettering and dimensions should be so clear that no misunderstanding is possible. Dimensions not given should never be scaled by the draftsman or workman, but the actual value should be ascertained by consulting some one familiar with the work.
Classification of Drawings. The classes of drawings which are made in a structural drafting room are: the stress sheet; the assembly, or general detailed, drawings; and the shop drawings, or, as they are more often called, the detailed drawings.
The stress sheet is a tracing upon which is usually shown a skeleton outline of the structure upon the lines of which are marked the stresses which are caused by the traffic or other forces to which the structure is subjected, and also the size and shape of the member designed to withstand these stresses.
The assembly or general detailed drawings usually give several views of the structure as it appears after it has been erected. On these views are shown to scale the members as they appear in the finished structure together with all the rivets and other details necessary for its completion. The overall dimensions are usually given and also any other dimensions which are necessary for the draftsman to complete the shop drawings. While the size of the members and their connections, as well as the number of rivets required, are always given, yet in a few cases the length of the member or shape and the individual spacing of the rivets are also given.
Copyright, 1912, by American school of Correspondence.
The shop drawings, or detailed drawings as they are more often called, consist of views of a certain member of the finished structure so dimensioned that it may be constructed by the men in the shop. It requires greater skill and more experience to make the assembly drawings than it does the detailed drawings, but in each case the men must be familiar not only with the drafting practice but also with that of the mill and the shop.
Drafting=Room Personnel. A drafting-room force consists of an engineer, a chief draftsman, squad boss, checkers, draftsmen, and tracers.
The engineer has charge of the plant as well as of the drafting room and is directly responsible for the ordering of all material, the manufacturing of the structure and its shipping to the place of erection. He conducts the correspondence, keeps track of the work in the drafting room and in the shop, and, in case his plant is one of many of a large corporation, makes weekly or monthly reports to his superior officers. In case his plant is a small one, the engineer usually does most of the work of designing and estimating.
The chief draftsman is directly responsible to the engineer for the getting out of the detailed plans or shop drawings and also ordering of the material.
The squad boss reports to the chief draftsman and his duty is to keep track of and to get out the drawings of any particular structure which is assigned to him by the chief draftsman. The squad bosses usually have from three to four to as many as twenty draftsmen under them, according to the magnitude or the number of structures which they are responsible for.
In addition to the draftsmen are the checkers, certain men usually of great experience in matters relative to mill and shop as well as drafting-room practice. It is the duty of these checkers to go over the draftsmen's work, see that all errors are corrected, and then finally sign it as approved. The checker only is held responsible for mistakes which then may be left upon the sheet.
The tracers are for the most part young college graduates or apprentices, and their office is simply to trace the drawings which are handed to them by the draftsmen.
A fireproof vault is always a part of the equipment of every well-equipped drafting office. In it are kept the notebooks in which the computations necessary for the design and detailing of the structures are kept, and also the tracings which have been made in the drafting room. In case the drawing of any particular structure is required, the tracing is taken out of the vault, blue prints are made, and the tracing returned as soon as possible. The vault should be so equipped that whenever the door is opened the interior becomes lighted. Aside from the mechanical convenience of this arrangement, it avoids the possibility of any person being accidentally locked in, since the rule is that in case of fire the vault should be immediately closed by the one nearest to it.
Assignment of Work. When the engineer of the plant received a stress sheet from his head officer or from the designing department in his own work, he hands it to the chief draftsman. The chief draftsman makes a record of it and gives it to the squad boss who is most accustomed to that class of work. The squad boss in turn hands it to the checker or checkers and these men make details for the various parts of the structure and make layouts for the various joints. The engineer now orders the material which will be required to build the structure or assigns a checker to do so and then returns the stress sheet to the squad boss who assigns certain draftsmen to prepare the shop drawings for the structure. Draftsmen make the drawings and turn them over to the tracers to trace them.
After the tracer has finished the tracings of the sheets, he passes them to the checker who in the first place made out the details and layout and ordered the material. The checker goes over these tracings very carefully and sees that all dimensions are correct, that all material used is that which he ordered, and if the drawings are correct he signs his name to the sheet. If the dimensions or any other matter upon the drawing is found to be incorrect, the checker places a ring around it with his blue pencil which is used in checking and off to one side places the correct value. After all the apparent errors have been corrected in this manner, a consultation between the checker and the draftsman who made the drawing is held. The errors are pointed out to the draftsman who in turn checks the work to prove the checker's results. The draftsman then takes the drawing and makes the necessary changes and returns it to the checker.