Posted June 8, 2021

Drafting Technical Drawings for Machining: Prototyping and Production

drafting technical drawings for machining

The design process for a new part begins with product conception and mechanical design, followed by CAD layout and the generation of the CAD model for manufacturing. It is a complex process capped by creating a 2D drawing to support the fabrication of the part. Yet without the proper care, the drawing can cause many problems if made incorrectly or poorly maintained. To avoid these difficulties, let’s look closer at the process of drafting technical drawings for machining so that machine shops can manufacture new parts without errors.

The Necessity of Drafting Technical Drawings for Machining

At one time, technical drawings were the only method to communicate fabrication instructions to the machinists who milled and turned parts. With the addition of CNC technology to the machine shop, 3D CAD models became standard for their precision and ability to generate G-code programming language for the mills and lathes. The 3D CAD model simplifies machining parts and ensures greater accuracy, but a need still exists for the standard 2D drawing in the manufacturing process. Some of the reasons why a drawing is still essential include:

  • Drawings present easy-to-read and interpret information for engineers, machinists, and quality inspectors and serve as a quick reference for the part.
  • A drawing identifies the principal dimensions and features of the part, helping with both initial quoting and final inspections.
  • Drawings also call out special tolerances that exceed the standard tolerance, which isn’t part of the 3D CAD model.
  • A drawing will specify details such as threading or finishes and other information like part numbers, versions, and revision history.

Both prototype and production need this information for manufacturing, but a detailed 2D drawing still aids the prototype process. Using the drawing’s details, the machine shop can move quickly when setting up for the prototype, saving both time and expense. A successful 2D drawing includes several key elements.

Views, Dimensions, and Other Essential Drawing Elements

The majority of the part information a machine shop will need to manufacturer a new part should include these five elements:

  • Orthographic views: These comprise 2D views displaying the exact shape and contour of the part. Depending on the part’s complexity, this may include multiple versions of these views from different angles. These views typically have dimensions and call-outs for holes and threading.
  • Isometric (pictorial) views: Images of how the part will appear in 3D serve as a reference for understanding the orthographic views.
  • Section or detail views: A designer may pull out or expand a section or detailed view for complex areas, clarifying tight or internal areas challenging to see or dimensioned on the main orthographic views.
  • Manufacturing notes: This block of text specifies manufacturing instructions such as surface finishes or deburring requirements.
  • Title block: This drawing area consists of formatted cells for part names, numbers, revisions, and dates. It will also include part details, including materials and finishes, technical information like scale, tolerancing standards, and angle projections. The title block will also contain the company’s name and contact information.

Arranging and displaying the elements exceeds the scope of this article, but with these elements included, the drawing will have the information it needs for manufacturing. However, a few basic errors can quickly cause problems.

Drawing Problems You Should Avoid at All Costs

Designers create drawings in many ways but should avoid a few common errors. Particular drawing problems cause a lot of difficulties for the machine shop and will typically result in a delay until they can resolve them:

  • Dimensions: Sometimes, designers will reference a “theoretical location” for a dimension instead of something tangible. The best practice is to reference the dimension to a part feature such as an edge, hole center, or boss.
  • Revision history omitted: When a machine shop gets a drawing that doesn’t include a revision history table, they don’t know which version of the part is portrayed by the drawing. Therefore, the revision history table is essential for identifying the correct documentation and keeping the communication clear between the customer and the machine shop.
  • Mismatched models and drawings: Designers often change either the 3D CAD model or the drawing and then neglect to update the other. Changing a value, such as a tolerance, in one but not the other will cause confusion for the machine shop and slow down production. To prevent this problem, include the revision history table on the drawing and establish a clear documentation control procedure.

Working Together with Your Machine Shop for the Best Communication

Some of the finer details of drafting a technical drawing for a part that will aid the machine shop during manufacturing:

  • Use a standard tolerance and only call out unique tolerances on the drawing.
  • Draw dimensions cleanly and do not overlap other dimension lines.
  • Call out both the tapped hole depth and the tap drill depth.
  • Call out the allowable external thread relief.
  • Use drawing notes for required certificates such as ITAR requirements, first article inspections (FAI’s), material certifications, bag-and-tag, certificate of conformity (COC’s), and engraving.

As evidenced here, great documentation leads to great parts. If questions arise on how to create 2D drawings, check with the machine shop. They provide the most reliable resources for documentation best practices.

At Plethora, we specialize in manufacturing precision parts using the industry's most advanced CNC machining equipment and software. To ensure that your part is built precisely to specifications, we use both your CAD model and 2D drawing in our workflow. We are an ISO 9001 certified machine shop, and our primary goal is to manufacture parts to the highest level of quality. Our online DFM and quoting systems are ready to receive your data so we can begin working together on your next project. To get started, upload your design files to Quote My Part or call us at 415-726-2256.
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The Plethora Team

The Plethora team is your go-to CNC manufacturer for hardware done right the first time. We have the tools and experience needed to create high quality custom parts quickly and with precision, whether you need a prototype or production run.

Topics: materials, finishing, CNC machining, Prototyping