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Engineering Design Drawing Levels

Updated on January 4, 2017

An Introduction to Drawing Levels

There are various levels of drawing packages; Level 1, Level 2 and Level 3.

Apparently there is a lot of confusion over what this means and where the dividing lines lie.

Basically it is the formulation of a design from a rough idea to a final producible and repeatable part or assembly. It’s a lot like a recipe for a meal. Mom would dump a bunch of leftovers in a bowl; throw in some canned stuff and say, “Hey, that’s pretty darned good. Now what did I put into this? I better write it down.” Mom wanted her meal to be repeatable and her thought process was very similar to that of a draftsman/designer who is thinking about setting ideas down on "paper."

The Means Of Recording An Idea in the Design Process

This sort of design process can be completely contained within a Computer Aided Design. Working from Concept to final Level 3 design can be done with one file although it is wiser to save off versions of each step in the design so that the designer can go back to an older version to review or redesign without starting over with a blank screen. It can also be a pencil sketch on a scrap of paper.

In addition there is a tendency to have conflicting needs that must be served. Marketing and management will want “cleaned up concept art” derived from Level 1. While Engineering will want Levels 2 & 3 drawings during evaluation. Production will want Level 3 drawings because they do not want to be responsible for the design issues so they want everything detailed out for them. So what are the differences?

Level 1 Cell Phone Concept Sketch

A typical concept sketch
A typical concept sketch

Level 1 Drawing, sketch - concept art, idea set on paper

Level 1 – Conceptual and Developmental Design, This your stereotypical “Sketch on a Napkin.”

I have literally been handed such a sketch and was asked to commit to a schedule and cost estimate for the completed design. More often this sort of a sketch would be used to “sell the concept” to management for them to approve funding. Where upon you are immediately asked how much it will cost and how long will it take to get it done. So you need to be prepared and familiar with all aspects of prototype design and production because that is what comes up in Level 2.

A Level 2 drawing. This is used to determine where there may be any errors or difficulties in fabrication. This part could be 3D printed or machined out of metal.
A Level 2 drawing. This is used to determine where there may be any errors or difficulties in fabrication. This part could be 3D printed or machined out of metal.

Level 2 Drawing, prototype

Level 2 – Production Prototype and Limited Production, This is sometimes referred to as the “First Cut.” The original design will not survive the review process that follows. It will be modified or on occasion it will be removed from consideration due to cost or schedule problems. On rare occasions it will be dismissed as “impossible” and “it will never work.” That is the designer’s chance to fight for the design and “sell” it again.

Once the designer is given the go ahead the design is finalized into a prototype drawing.

A prototype drawing provides enough information to produce a one-off part and there is a lot of leeway for variation as problems are discovered and resolved. For example there could be several parallel designs that use different materials or different configurations. The phone might be prototyped using a 3D printing process, one in metal and the others in different types of plastic. One design could have a touch screen while the others have actual buttons. There could be variations in the data and charging ports.

The Level 2 Drawing is where the idea is brought into reality. The drawing is left open to some interpretation especially regarding fasteners, materials, surface finishes and color schemes. The point is to create a working prototype that can be handled and tested.

Once the design is finalized there may be several prototypes built to test the process of producing the design so that any tooling or processes needed are tested and in place.

Transition Drawing, Level 2 to Level 3

Level 2 transitioning to Level 3  Electronics Subassembly
Level 2 transitioning to Level 3 Electronics Subassembly

Level 3 Drawing - The final level

In level 3 drawings, all of your i's must be dotted and t's crossed, with nothing left open to varying interpretations. Unless it’s a simple part, this will necessitate a drawing package made up of the top assembly, subassemblies, part drawings and a bill of materials.

In the unfinished subassembly shown below there are at least eight subassemblies made up of over 30 part types. Everything that has to be fabricated will have a part number and drawing assigned to it. The purchased electronic components and fasteners will not. They will be part of the Bill of Materials as purchased items.

There should not be any corrections required to the design because it has been proven out in prototyping. All the missing dimensions, typos and poorly expressed instructions should have been corrected by this time.

Any revising should be due to changes to the design requirements over time. For example the electronic components changed size or a different means of fastening the parts superseded the old style fasteners then there would need to be a revision change to accommodate that change. These sorts of changes tend to cause a ripple effect throughout the design.

Level 3 Assembly with sub assemblies

A production assembly, which itself is a sub assembly, using the sub assembly shown above
A production assembly, which itself is a sub assembly, using the sub assembly shown above


Like a recipe, the design’s success or failure depends on adequately transferring the needed information including intent to other interested parties. Otherwise the soufflé may collapse.

Applicable Reference Documents

ASME Y14.24 – 1999 - Drawing types

MIL-STD-100G (NOTICE 1) DEPARTMENT OF DEFENSE STANDARD PRACTICE FOR ENGINEERING DRAWINGS (14 DEC 2001) [S/S BY ASME-Y14.100, ASME-Y14.24, ASME-Y14.35M, AND ASME-14.34M]., MIL-STD-100G, dated 9 June 1997 is hereby canceled. Future requirements for engineering drawings should refer to the following American Society of Mechanical Engineers (ASME) standards and Appendices thereto, as applicable:

ASME-Y14.100 describes Engineering Drawing Practices in general, it establishes engineering drawing practices and pulls together the engineering drawing and related documentation practices in the Y14 series. This Standard is not a stand-alone document

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