July/August 2010 - Joining the metal trades in any capacity means, among other things, learning to communicate to get products manufactured.

The metal industry uses the technical languages ANSI and ISO with applications in geometric dimensioning and tolerancing (GD&T).

I am not going to discuss the advantages and disadvantages of ANSI versus ISO. Rather, I will demonstrate the implementation and use of these important communication tools in manufacturing engineering.

The symbols and nomenclature are identical for ANSI and ISO. What are the differences, then, and how do people indicate and notice them?

Identification
The identifying symbol for ANSI includes a round shape on the left and a trapezoidal shape on the right. The shapes are reversed for ISO.

ANSI uses third-angle projection, and unless otherwise stated, all dimensions are in inches. ISO uses first-angle projection, and unless otherwise stated, all dimensions are in metric units.

A "bilingual" approach includes setting the primary dimensions in one measurement form, either inches or metric units, and next to them, in parentheses, giving the dimensions in the other form.

In our global economy and with the world-market approach, it is essential to know about ANSI and ISO applications in manufacturing engineering.

Measurements
The common perception is that it is difficult to use ISO. This is not the case, however. It just takes some understanding of rules and how to measure.

For example, the metric system is based on the rule of 10. While the metric system works on base 10, the U.S. system favors base 12.

In general, measuring consists of the numerical comparison of the length to be measured with a physical measuring instrument. The observation obtained is the real value.

Physical quantities are calculated in units. When comparing length, for example, differences are specified in meters or yards. These amounts, too, are denoted by unit systems: meter (m.) and yard (yrd.). The first thing you should look at on a print is the title block, which will indicate by symbol whether the print is according to ANSI or ISO.

The next step in preparation for any further action in manufacturing engineering is understanding the difference between ANSI third-angle and ISO first-angle projection.

Last but not least, there is the application of ANSI and ISO with GD&T. A very big help is that all the symbols for both ANSI and ISO are identical. The differences are mainly in the reference view. FFJ