My friend, Mr. Vin is over 80 years old, and the epitome of old time engineering. He works at a drafting table with a workbench, and behind him are the facilities to create and assemble antenna electronics and housings. His company has given him a small work area that has a sheet metal fabrication shop area with a sheet metal shear (to cut) and a finger-break (for bending sheet metal), as well as assorted hand tools. He continually invents new communication antennas for airborne, landbased, shipboards and vehicular military and commercial use.

When Mr. Vin would convert the customers statement of work in his mind, he said he would have a mental picture of the product and how it operates. He would then create a physical prototype to be tested, verified and validated within a day or two. During this process Mr. Vin would establish in pencil, a multiview isometric engineering drawing with specifications and fabrication requirements in accordance with ANSI/SME Y14.

Today, 21st century academically trained engineers would use SolidWorks 3DCAD or other computer software. These academically trained engineers would also take about 5+ weeks to mirror what Mr. Vin can do in just a day or two. They would end up with ambiguous or wrong symbols, and abbreviations. This would go against configuration management of the customer key characteristics, causing a rejection on delivery, and sometimes a battle over cost.

Establishing a drawing correctly is very important, and can become complex if the rules are not followed. There is an “Alphabet of Lines” in accordance with ANSI/SME Y14 that allows the mechanic, fabricator or builder to have a visual image of what the product looks like based on the way the line is drawn. The Alphabet of Lines pictured here is just on example of how the line is drawn to provide the end user with mental picture of the product the engineering is presenting.

Many engineers and/or the mechanics who use the drawings are not educated on the correct use of Key Characteristics, or what is often referred to as “Feature Control Frame and Datum Order of Precedence” indicators.

The indicators give vital communications to a manufacturer, that if missed, can cause all the profits in a part to disappear during the production or upon completion of a job.  In the middle of the feature control frame is a circled “M,” or a “Tolerance Modifier.” We sometimes call the Tolerance Modifier a Bonus Tolerance because this tolerance can reduce the manufacturing costs significantly.

What it allows is an adjustment to a dimension indicated by the Feature Control Frame. The Feature Control Frame shown in datum A, B, and C indicates the dimension’s most important point of measurement. The tolerance 0.025 can be modified within the upper and lower limits from the datum points on the drawing.  An example of the Tolerance Modifier applied to a drawing is shown in the Projected Tolerance Zone Application drawing.

The bottom line – if the drawing is not in accordance with ANSI/SME Y14 it would be like reading a story with missing words.