How to Create an Effective Technical Drawing

Creating a good technical drawing is an essential skill for engineers, designers, and manufacturers. A well-crafted technical drawing serves as a universal language that communicates complex information clearly and accurately, ensuring that all stakeholders can understand the design intent and specifications. Whether you are designing a simple component or a complex assembly, a precise and detailed technical drawing is crucial for successful production, quality control, and maintenance. In this blog, we will explore the key elements and best practices for creating high-quality technical drawings that meet industry standards and effectively convey your design ideas.

Technical Print from Scratch

A Shift Towards CAD-Centric Manufacturing

In today’s manufacturing landscape, most projects begin as 3D CAD models. Manufacturers leverage these digital tools to produce manufacturing instructions for computer-controlled machinery, such as CNC machines and 3D printers. Software like CAM takes the 3D model and generates the necessary toolpaths and movements for production. As a result, the technical details traditionally captured in drawings or prints often serve more as references than as the primary guides for manufacturing. Many standard dimensions might be omitted from the actual print drawing, with the expectation that the 3D CAD software will direct the creation of these features and dimensions not explicitly shown in the drawing.

The exclusion of non-essential measurements in contemporary prints highlights a significant change in manufacturing practices. The industry’s approach has shifted; whereas technical drawing prints were once deemed the primary source of information with CAD files as secondary, the roles have now reversed. Today, CAD models are the primary reference, and the printed drawings serve as supplementary documents. When discrepancies arise between the CAD model and the drawing, the CAD model usually holds the authoritative position.

How to Create a Technical Drawing from Scratch

It’s crucial to remember that technical drawings for manufacturing are vital documents—they guide every machining cut, forming operation, and critical feature during production. Errors resulting from ambiguities in the drawing can incur additional costs due to the need for rework or part replacement, and can cause project delays. Many machine shops reject projects with poorly drafted drawings that lack dimensions, have unclear design features, or exhibit substandard detailing. When collaborating with a manufacturer through a service like Modo Rapid, such issues can result in extensive back-and-forth communication between all parties involved.

To minimize the likelihood of receiving drawings back from the manufacturer with numerous corrections and requests for changes, it’s imperative to produce clear technical drawings from the outset.

Here is a guide of best practices to assist engineers in creating clear and professional manufacturing drawings on the first attempt. These guidelines are applicable to both 2D drafting and generating technical drawings from a 3D model.

1.Develop a Template

Establish a standardized template for both detail and assembly drawings that adhere to ASME or ISO standards, depending on your region. The title block, located in the bottom right corner, should include company or organization details, names of the responsible individuals (designer, checker, approver), drawing title/name, revision reference, sheet size, view alignment method, and primary scale. Additionally, include a section in the title block to specify default tolerances not shown with the dimensions on the drawing. A parts list can be positioned above the title block to enumerate any additional parts or components required for assembly, referencing each item by the drawing’s title or page number.

Create a template.

2.Include Coordinates and a Notes Section

For large or complex technical drawings, it is advisable to incorporate coordinate divisions along the border to serve as reference points when discussing specific dimensions or features. Reserve space in the top left corner of the page for a notes section to detail materials and coding specifications, relevant standards, special manufacturing instructions, and other essential information. Notes pertaining to particular features or the entire drawing can be referenced within the part drawing using triangular flags with the corresponding note number.

coordinates and a notes list.

3.Verify Scale and Units

Make sure the drawings fit properly on the page and that dimensions are easily visible in each view. If you intend to have the part manufactured internationally, it’s advisable to use the metric system for dimensions. In the US, using imperial measurements is standard practice, as most manufacturers program their machines with the imperial system, though they can interpret both measurement systems. When unsure, include both sets of measurements in a dual-dimension layout.

scale and units.

4.Ensure precise tolerancing

It’s advisable to select appropriate tolerances for modern CNC machining, typically within the range of +/- 0.005” for linear dimensions. Modo Rapid provides a framework of standard tolerances for various manufacturing processes in its guidelines. Tolerance adjustments may be necessary based on part complexity and production techniques, but adhering to standard tolerances can help streamline design expectations and minimize expenses. Tolerances tighter than the standard range are deemed “high precision,” while those broader are categorized as “relaxed tolerances.”

correct tolerances.

5. Develop standard formats for future sheets

To facilitate future revisions, establish a template featuring a continuation title block and a revision table positioned at the upper right corner. The revision table should include details such as the revision date, the rationale behind the changes, and the revising individual’s name. Additionally, ensure that both the initial and subsequent pages of the drawings clearly indicate the page number and total page count at the lower right corner.

6.Verify view alignment matches the projection standard

When initiating the drawing process, it’s crucial to ensure accurate alignment of projections. The chosen orientation will guide the fabrication process, making it essential for all views to adhere to the specified alignment convention indicated in the title block. In the United States, third angle projection is customary, whereas in Europe, first angle projection prevails as the norm.

Ensure views align with the projection view.

7.Incorporate an isometric view whenever feasible

When space allows, it’s beneficial to integrate a 3D isometric view into the drawing to assist the machinist during the manufacturing process. These views aren’t constrained to the same alignment as the orthographic views, but it’s essential to ensure they are drawn from the appropriate corner to convey the desired orientation accurately. Isometric drawings should omit dimensions due to scale differences, but they can include explanatory notes. In addition to enriching the understanding of the part in three dimensions, isometric views can provide valuable insights such as the installation direction for inserts or pins in assemblies.

Rapid Prototyping Techniques

8. Minimize the use of hidden lines

An overabundance of hidden and tangent lines can diminish the clarity of a drawing. Prioritize the inclusion of essential hidden lines, while noting others for clarity on an isometric drawing or detailing them in an exploded view for smaller features.

9.Emphasize Dimensional Clarity

Ensure that dimensions are positioned exterior to the main view, and avoid any crossing of dimension lines to maintain clarity. Carefully review for redundancy, eliminating duplicate dimensions present in other views or already specified within the 3D model’s title block tolerances. Highlight critical areas requiring dimensioning, including reference dimensions, GD&T specifications, thread details, and surface characteristics. When dimensioning arcs exceeding 180 degrees, prioritize diameter measurements, while arcs below 180 degrees (such as fillets) should be labeled by their respective radii. Avoid redundant angle dimensions when two dimensions form a right angle. Supplementary dimensions, like total length consolidating multiple smaller measurements, can be included for reference enclosed within parentheses.

10. Provide Comprehensive Material and Surface Finish Specifications

Merely mentioning the metal type is insufficient. For instance, Stainless Steel 304 encompasses various ASTM specifications tailored to different applications. Additionally, elaborate on any specific surface finishing directives, encompassing details like edge breaks and deburring requirements. Incorporate these particulars within the notes section of the drawing to ensure clarity and adherence to precise specifications.

specifications for materials and surface finishes.

11.Specify Threads with Detailed Thread Specifications

Threads come in various classes, fits, and configurations tailored to specific applications. Therefore, it’s imperative to identify threaded features with complete thread specifications. This entails detailing the thread form, series, major diameter, threads per inch, class of fit, and depth as a minimum requirement. Utilizing standard threads is advisable to facilitate the use of readily accessible tooling. In cases where a completely bespoke thread is necessary, employ a detail view to comprehensively define the thread form.

 threads with complete thread specifications.

12.Select the Appropriate Linear Tolerance

In manufacturing, tolerances play a crucial role in ensuring that parts maintain their intended form, fit, and function despite inherent variations. Engineers utilize three primary types of linear tolerances:

  1. Bilateral Tolerances: These allow for variations in both positive and negative directions from the nominal dimension (e.g., ±0.005″).
  2. Unilateral Tolerances: Variation from the nominal dimension is permitted in only one direction (e.g., +0.005″ / – 0.000″).
  3. Limit Dimensions: Representing the largest and smallest permissible values, limit dimensions encompass a range where any dimension within is considered acceptable (e.g., 0.525″ / 0.520″).

While bilateral tolerances are commonly employed for general tolerance definitions due to their versatility, unilateral tolerances and limit dimensions serve to highlight critical fit dimensions and tightly toleranced features. However, it’s essential to use them judiciously to maintain the clarity and readability of the drawing.

 appropriate type of linear tolerance.

13. Control Geometric Features Using GD&T

GD&T, or Geometric Dimensioning and Tolerancing, serves as a vital method for engineers and designers to convey precise requirements to manufacturers. Beyond specifying tolerance values, GD&T employs symbols, datums, and geometric characteristics to delineate the acceptable variation in features. This methodology proves particularly valuable in intricate parts where precise control over geometry is essential. Various types of geometric tolerances include:

  1. Form Tolerance: Governs deviations from the ideal shape of a feature, not reliant on a datum.
  2. Orientation Tolerance: Dictates the shape of a feature concerning a specified datum.
  3. Location Tolerance: Specifies the position of a feature relative to a datum, commonly used for defining hole locations.
  4. Run-out Tolerance: Sets the allowable deviation when a feature rotates around its centerline, necessitating datums.
  5. Profile Tolerance: Determines the acceptable deviation of a profile line or plane, without requiring datums.

Standardized symbols and methodologies ensure clarity and consistency in GD&T application, mitigating confusion with manufacturers. However, it’s crucial to strike a balance, avoiding over-specifying drawings, which could impede interpretation.

Control geometric features with GD&T.

14. Clearly outlining finishing requirements is essential

Providing detailed instructions solely through notes might prove challenging for manufacturers or post-processors. To facilitate clarity, incorporating color-coded views or cross-hatching can be immensely beneficial, particularly for parts necessitating specific areas or features to be masked. Additionally, for processes like anodizing with distinct specifications, including the specification directly in the call-out is advantageous. The overarching goal in conveying post-processing requirements is to eliminate ambiguity and ensure thorough understanding.

In the realm of technical drawings for manufacturing, clarity reigns supreme. It’s crucial to dedicate sufficient time to ensure each detail is unmistakable and aligns with established standards. Moreover, subject your drawing to rigorous quality assurance and approval processes. A drawing that is easily understandable and precisely outlines your requirements lays the groundwork for a seamlessly produced part.

Once your drawing and 3D CAD files are prepared, you’re welcome to contact us.