How to Create a Good Technical Drawing

Two-dimensional technical drawings have been part of the engineering process since before the printing press. According to Interesting Engineering, perspective drawing was invented in the 1300s. The first technical drawings for manufacturing were perspective drawings of real objects. Centuries later, the invention of descriptive geometry (1765) and orthographic projection (1770), helped engineers give visual form to their ideas. From this point until the introduction of 3D CAD modelling in the 1980s, 2D technical drawings were the main way engineers documented their designs. This blog will delve into the best practices involved when developing a technical drawing.

A Paradigm Shift to CAD-Driven Manufacturing

Today, most projects are designed as 3D CAD files from the start. Heavy steel fabrication companies use digital tools to generate manufacturing commands for computer-controlled machinery such as CNC machines or equipment for 3D metal printing. This planning software, such as CAM, uses the 3D model to create toolpaths and movements for the manufacturing process. The technical information captured on a drawing or print might only be used as a reference rather than a definitive guide for manufacturing, especially since some of the standard dimensions may not be included in the actual print drawing. Instead, it is assumed that the 3D CAD program would guide those feature sets, or dimensions, not shown on a drawing.

Technical Drawing Best Practices

• Create a template – Create a single template that can be used for detail and assembly drawings compliant with ASME or ISO standards (depending on location). The title block in the bottom right corner must include company or organization information, names of the people responsible for the drawings (designer, checker, approver), drawing title/name, revision reference, sheet size, view alignment convention, and primary scale.
• Add coordinates and a notes list – When creating large or complex technical drawings for manufacturing, it is good practice to include coordinate divisions along the border as reference points when discussing a dimension or feature.
• Check scale and units – Ensure that the drawings fit on the page and that the dimensions will be clearly seen in each view. If the part to be manufactured abroad, it is best practice to use the metric system for dimensions.
• Ensure correct tolerances – Generally, it is best to choose reasonable tolerances for most modern CNC machines, typically around +/- 0.005” for distance dimensions. Tolerances narrower than the general range are considered “tight tolerances,” and those wider than the general range are “loose tolerances.”
• Create templates for subsequent sheets – In preparation for revisions, create a template that has a continuation title block and a revision table in the top right corner which displays the revision date, the reason for the change, and the name of the person who made the revisions.
• Ensure views align with the projection view – Once one starts drawing, it is important to use the correct projection alignment. The person fabricating the part will use this orientation during manufacturing, so make sure that all the views follow the alignment convention that is specified in the title block.
• Include an isometric view – If there is room on the page, it is good practice to include a 3D isometric view to help the machinist when manufacturing the part via rapid prototyping. These do not need to be in the same alignment as the orthographic views but it is important to make sure that they are drawn from the correct corner for the orientation to be shown.

 Closing Thoughts

Overall, clarity is the most important factor in any technical drawings for manufacturing and steel fabrication Australia. It is necessary to take the time to ensure that every detail is clear and the drawing complies with the accepted standards. Additionally, it is important to ensure that the drawing undergoes all quality assurance and approval procedures. A drawing that is easy to follow and clearly defines business requirements is one of the first steps to a successfully manufactured part!