Free Proof that the DQAT GD&T Program saves your company money!!!

1. GENERAL:

Often a common misconception of GD&T is that it is simply a series of symbols to eliminate words here and there. Sometimes there is an impression that its understanding should be somewhat automatic without much training. GD&T tends to be the "Rodney Dangerfield" of the industrial world; it "gets no respect." The true power and magnitude of the system is not recognized. Thus, there is a tendency to dismiss it almost entirely as another gimmick to upset our work schedules and cause confusion. There may be a decision to minimize any training efforts to the barest of necessities. However, GD&T is an entire universal language of engineering statement.

For the above reasons the following information is designed to explain some of the certain advantages the GD&T system offers that do not exist in coordinate dimensioning and tolerancing. Following is an overview of what you can expect from a DQAT, INCORPORATED Program in the way of; SAVINGS, TRAINING, and IMPLEMENTATION.

2. SAVINGS:

2.1 Engineering - According to Donald E. Day, Chairman, Mechanical & Quality Technologies at Monroe Community College, Rochester, NY; "It is estimated that over 80% of the engineering documents generated in the United States are flawed in some way. Often the ideal geometry is well defined. It is the amount of acceptable variation or tolerance from the ideal or nominal geometry that is usually unclear." The coordinate system of dimensioning and tolerancing on drawings;

• Do not define geometric requirements and relationships adequately.
• Often result in rejection of good parts or acceptance of functionally unacceptable parts.
• Often do not provide adequate information for efficient and consistent inspection.
• Result in tolerances accumulating in unacceptable ways.
• Use notes to define needed geometric controls that are often difficult to understand and interpret.

The GD&T system is a concise engineering language that helps overcome these short-comings. Defining the functional requirements and Datum Reference Frames for the parts requires more time than with the outdated system. Yet even the effort invested within the Engineering Department to implement GD&T can be paid for via the greatly reduced amount of expensive drawing revisions.

2.2 Manufacturing and Inspection - When GD&T is properly applied and understood, product costs go down because:

• Engineering can accurately define what is required. This can cut down time taken to interpret the requirements by 25%.
• Inspection setups are not subject to interpretation. The lack of trail-and-error may, in some cases, save as much as 40% in gages that often get scraped.
• Everyone can do their jobs right the first time, resulting in a reduction of a possible 25% less Material Review Board action.
• Datum systems speed up manufacturing and inspection and provide an effective basis for SPC. The savings vary and are difficult to determine, but they do exist.
• Accumulated benefits of GD&T often enable lower and more accurate price estimates for fabrication.

The February, 1995 issue of Quality Progress printed an article written by Collin Wearring and Dennis P. Karl entitled "The Importance of Following GD&T Specifications." A simple flat plate with 4 holes in it was used to illustrate that "importance." The difference in inspection results was profound! Quoting the article;

"Simulation results indicate that the percentage of parts passing the inspection gauge was approximately 99% when following the GD&T specifications, but dropped to approximately 20% when both improper features and improper positioning sequence were used (about 80% of good parts were rejected). All the results are measurements from the same parts, the only difference being the positioning features and sequence used during inspection."

2.3 Assembly - One of the most costly items for a manufacturing facility is to "shut down the production line." Since the entire GD&T system is based on the function of the mating parts, the use of pry bars, hammers, and expensive rework is no longer necessary. This alone could possibly save 20% in the overall costs of assembly.

Al Neumann, in his Geometric Dimensioning and Tolerancing Workbook writes; "Engineering, manufacturing, and inspection all share a common three plane concept. These three mutually perpendicular planes are perfect and exactly 90 degrees to each other. In geometric tolerancing we call this the datum reference frame. In mathematics we call this the cartesian coordinate system." All mating parts are affected by this truth, and assembly lines cannot help but be affected in a most positive fashion when function, fabrication, and verification are in harmony.

3. TRAINING:

3.1 Who should be trained in GD&T and in what order? The following is a logical order for such training when implementing GD&T on an entire project and across all departments:

• All designers and engineers.
• Purchasing.
• Vendors and suppliers as required.
• Manufacturing engineers.
• Quality Control and Quality Assurance.
• Inspection.
• Tool designers and model makers.

Note: The order may change or training classes may be mixed as needed.

3.2 Class size - The ideal class size for GD&T training is 15 maximum. But more may be included with the understanding that everyone participates. The length of initial training should be 20 hours minimum class time, and 20 hours minimum consulting time.

3.3 Cost - The initial cost of GD&T training is a matter of simple math: the cost of the instructor plus the man-hours spent in class by each person. Like any training, there is also a certain amount of time outside of class required. This may be done on the individual's own personal time since he/she also benefits from this general knowledge.

4. IMPLEMENTATION:

4.1 How long does it take for engineering personnel to become proficient in GD&T? On the average, with constant use, engineers and designers can gain enough proficiency to properly apply GD&T to working drawings in approximately 3 months. As far as all departments in the corporation are concerned, Lowell W. Foster, PE writes; "Full integration and use can be anticipated within 1-2 years as an approximation."

4.2 When should a company "cut in" GD&T? The best time to begin a full-blown GD&T program is at or near the beginning of a new model design. However, much can be gained by using the GD&T method of dimensioning and tolerancing at any time.

4.3 What about existing drawings that are used on a new (GD&T) program? Tooling costs are always a consideration: but the best approach is to update the affected drawings with GD&T relating to the established Datum Reference Frames. It is also necessary to consider interchangeability with existing models.

5. CONCLUSION:

It is obvious that this dissertation cannot give actual numbers of people nor actual dollars that can be saved at without accurate information about present manpower usage and lost time and money using the coordinate system of dimensioning and tolerancing.

Lowell W. Foster, PE, President and Director of Lowell W. Foster Associates, Incorporated has this to say about a GD&T program; "A GD&T program should be strong and well managed but yet remain as low-key as possible. It must fit into the surrounding disciplines and activities, but remain a high priority effort. GD&T, correctly managed and implemented, will provide its own momentum for on-going success into the future. Any subject worthy of addressing as a priority item deserves a best effort. Geometric dimensioning and tolerancing is surely worthy of that effort and will bring manifold rewards into the future. Successful integration of GD&T as a regular resource and practice, will provide a giant step into world class engineering and enviable stature in the organization's field of endeavor."