An engineering drawing is a language of an engineer to communicate the technical requirements. The drawing requirements are directly related to an engineering design intent. The design engineer provides the necessary specifications in drawing to meet the customer needs. The drawing is a resource for downstream users like Manufacturer, Quality engineer, Assembly engineer, Supplier, and other cross-functional teams. The manufacturer needs for manufacturing the part physically. The quality engineer needs it for inspecting the specifications. Assembly engineer needs drawing for fitting parts on the machine. The supplier also needs a drawing to supply parts based on the requirements.
Earlier to create handmade drawing was a bit difficult task. Due to available advanced software in the market now, it is pretty easy even to model complex 3D parts along with the detailed drawing. The drawing is a sheet in which figures, dimensions, tolerances, bill of materials and other specification notes related to part/assembly are present.
It is a legal document that helps understand desired objectives from different cross-functional teams. These objectives are critical to meet customer expectations. Nobody should deviate from drawing specifications. The part will go for rework or rejection if specifications are not justified. Different views are used to show details in the drawing sheet. First angle method projection and the third angle method projection are the two methods used to display views in the drawing.
The drawing sheet should have sufficient space to show details. If views are smaller or larger, then different drawing scales can be utilized. The drawing sheet can be of portrait or landscape type based on sheet size selection. A4, A3, A2, A1, A0 are the commonly used sheet sizes for engineering drawings.
It’s difficult to imagine the manufacturing of parts without having an engineering drawing. Orthographic projection and Perspective projection are the methods commonly used. The Orthographic projection method is the most common for mechanical design engineers. Nowadays it is a general practice to have a 3D view provided in the drawing, to assist the user for better visualization of the part. The 3D view can be of Isometric or Axonometric type. Types of views are like sectional views, detail views, auxiliary views, and uninterrupted views in an engineering drawing.
An engineering drawing has one sheet or multiple sheets based on the complexity level of the parts. Multiple sheets used are for assembly, fabrication, machining, and painting purposes. An example figure is shown below for demonstration purposes showing engineering drawing views (front view and side view).
The figure shown above is a simple plate with allowable tolerance. The part will go for scrap if tolerances are out of specification. There could be other requirements too along with dimension details like plating notes, painting notes, surface finish, and material callout. The respective guy will not allow the part to pass the gate till it meets all requirements. All requirements in the drawing need to be met by all cross functions or departments responsible for making this part. Hope this document will serve the purpose of understanding an engineering drawing. Wish you very happy learning!!