Technical Drawing Basics

• A Technical Drawing is a visual representation of a product or system that communicates how the product or system is intended to function or be assembled.

  • Technical drawings are used in a variety of fields, such as engineering, architecture, and manufacturing, to clearly and accurately convey information about the design and function of a product or system.

  • They are 2D, standardized instructions for how something should look/be, including specifications of: Shape, Size/Dimension, Material(s), Quantity, Finish/Coating, etc.

  • They can also describe how to perform an action/process, typically related to manufacturing: Assembly instructions, Machining instructions, Welding/Fabrication instructions, etc.

• Technical Drawings are sometimes also known as (AKA):

  • Blueprints - called such because they were originally made on blue-colored, light-sensitive paper

  • Schematics

• On most technical drawings, there are at least 5 key features:

  1. Title Block

  2. Views/Projections

  3. Dimensions & Tolerances

  4. Revision Block

  5. Notes

Dimensions & Dimensioning

• Dimensions can be categorized by two different types:

  1. CRITICAL = Very important to the fit/form/function of the design, typically have tighter tolerances relative to the design as a whole

     • Usually exist where features/parts mate with other features/parts

  2. Non-Critical = Less important to the fit/form/function of the design, typically have looser tolerances relative to the design as a whole

• Technically-speaking, some basic dimension types include:

  1. Linear

     • Measures distance from one object to another

     • Units = Metric/ISO (mm, cm, m) or "Standard"/"Imperial"/ANSI (in, ft, yd)

  2. Angular

     • Measures the angle between two non-parallel lines

     • Units = Most commonly in Degrees (°) but sometimes in Radians (rad)

  3. Radius

     • Measures the linear distance from the center point of an arc/circle to an edge (ex: halfway through a circle)

     • Units = Same as Linear dimensions, represented by the (R) symbol

  4. Diameter

     • Measures the maximum linear distance from one "side" of an arc/circle to the other (ex: line completely through a circle, intersecting the midpoint)

     • Units = Same as Linear dimensions, represented by the (⌀ / DIA) symbol

  5. Depth

     • Measures the distance from one parallel surface to another, or the distance from the exit of a hole to the hole bottom

     • Units = Same as Linear dimensions, represented by the (↧) symbol

• Additionally, there are two major dimensioning styles/strategies:

  1. Baseline/Coordinate Dimensioning

     • Dimension reference the same starting location, called an "origin":

Tolerances & Tolerancing

• Tolerance is acceptable allowance for deviation/variation from a target dimension/measurement

  1. "Higher tolerance" = less allowance for deviation/variation

  2. "Lower tolerance" = more allowance for deviation/variation

• Well-toleranced technical drawings are very important, as they keep difficulty to manufacture – and therefore, cost, time, & probability of success – to a minimum

  1. Focus on keeping tolerances tight only when needed, particularly with Critical features of parts

• Generally-speaking, there are two different kinds of tolerances:

  1. General Tolerances

     • Usually called out in the title block, these apply to an entire set of dimensions, typically based on how many decimal digits are on a given dimension