chapter  6
13 Pages

Marking out and measuring

A body repair worker must have a good general knowledge of engineering drawing and surface developments in order to mark out replacement parts on sheet metal, as this requires accurate calculation of sizes and angles. While the majority of body workers who work in the repair side of the industry do not have to perform a lot of difficult marking out from elaborate drawings on to sheet metals for the making of the articles, those employed in the manufacturing side of the industry (e.g. coachworks) have to mark out all units and assemblies from drawings, whether for a one-off item or for ‘mass’ production. Consequently a thorough knowledge is essential of measurement and marking tools, and also of how to check these tools so that a standard of accuracy can be achieved and maintained throughout. Blueprints, as working or production drawings are

generally termed, are photographic reproductions of an original drawing. They take their name from the colour of the finished print when the drawing is reproduced on ferro-prussiate paper. This paper produces copies of the drawing in white lines on a blue background. Several other types of coloured prints are also produced by industrial contact photo equipment, but in spite of their colour these are still generally known as blueprints. The practical bodyworker is rarely called upon to produce a finished drawing, but will find it necessary in many cases to understand and work from both general and detailed drawings as set out by a skilled draughtsman. The main object of reading a drawing is to obtain a clear mental picture of what another person has represented on paper by means of a conventional arrangement of lines and symbols. To this end the value of hand sketching cannot be too fully emphasized, as well as the

making of simple models, for a much clearer impression of form can be obtained when movement and touch are combinedwith sight. The skilled technician, particularly in the small workshop or garage, is generally responsible for seeing his work through all stages of manufacture, commencing with careful study and accurate interpretation of the drawing. Before actual manufacture can begin, it is necessary to set out the desired shape by marking the outline on the surface of the sheet of material. Automobile work demands a thorough knowledge of the methods of sheet metal work, and although the machine has displaced the technician for certain operations there is an increasing demand for technicians who are capable of developing the large variety of work met in the industry. Much of the work done deals with doublecurvature shapes which are in some cases fabricated by hand in sections. This type of work needs templates made to the exact curvature required so that the work can be checked at each stage of its progression. Also, very accurate alignment jigs have to be manufactured to hold these parts, after they are formed to the template size and shapes, so that they can be welded together into the finished component. Marked-out templates, which are usually in thin metal sheet, cut and then filed to a very accurate size, are used when one is working to rolling radii so that the curve can be checked as it is rolled. Angle templates are useful when bending in the bending machine to check the angle of bends so that they are constant.