Engineering Drawings: Specifications

A short series of lectures on Engineering Drawing as Part of MECH2400 5400: Mechanical Design 1 By Paul Briozzo

Specifications • Specifications are agreed upon defined requirements for a product

• Specifications are a type of Standard defined by a governing body

• Specifications may have embedded drawings but may focus more on text

• There are effectively two types of specifications;

• 1. Design or Product Specifications (what is wanted) • 2. Application Specifications (how something is to be done in

order to achieve a specific goal)

• Data sheets share some common points with specifications sheets.

From Week 1, Detail Drawing: An Example

The treatment or coating that the component is finished to is stated in the title block. If the process is a company or military standard that is often followed e.g. the aircraft industry, NASA, The Australian Army, then reference to a standard data sheet is made. This slide shows an open ended and overly basic material and finish specification that are both prone to misinterpretation.

Where do Specifications appear on a Drawing ?

Specification for Dulux Red Oxide Primer

Specification for Grade ST1 (SG Iron)

Design or Product Specification

A design or product specification describes the key points or requirements for a final design not how to achieve it.

Application Specification Application Specifications provide a sequential presentation of functions that need to be carried out in order to achieve a goal. The key difference between Performance and Application Specifications is that Performance specifications define a goal with no guidance on how this is achieved. Where as Application Specifications define a step by step set of instructions which lead to a common goal.

Data Sheets • A data sheet provides a summary of the typical performance a component. • Popular in the Electronics Industry for defining components.

A typical data sheet showing the summary of the typical performance a component. Source: http://www.lucidscience.com/pro-simple%20infrared%20illuminator-3.aspx Accessed 14/08/2013

MIL Specifications

Zeppelin Mobile Systeme GmbH

• MIL Specs are very stringent and are rigorously checked. • MIL Specs evolved to ensure that the performance of a design could be fully realised.

Gichner Mobile Shelter Systems

Norwegian Army Heckler & Koch HK416N with an Aimpoint CompM4 red dot sight and a vertical fore grip. Image by Dybdal

Side profile showing slot spacing of Picatinny Rail type rifle sight mounting system. MIL-STD-1913 (AR) 3rd of February 1995

Picatinny rail dimensions, cross section (dimensions in inches). MIL-STD-1913 (AR) 3rd of February 1995

NASA Specifications More stringent than MIL Specs More difficult to meet by contractors Add enormous amounts to the cost of an overall project Many Specifications deal with matters outside of spaceflight e.g. software design