ETImail: Online Geometric Dimensioning and Tolerancing (GD&T) Newsletter

ETImail is a regular online publication devoted to Geometric Dimensioning & Tolerancing. Each edition features a host of GD&T resources and links, as well as dimensioning tips by noted GD&T author and ETI founder, Alex Krulikowski. We also invite you to visit our website, etinews.com. To view past issues of ETImail, see the archives.

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A Tale of Two Companies: How GD&T Saves Money in Each Aspect of Design and Production

Alex Krulikowski

Companies that use GD&T produce better designs, waste less time and save money. This article takes a look at precisely how using GD&T saves money in each aspect of design and production.

The identities of companies described in this article were protected by altering their names and other characteristics, but the events and results involved have been preserved. Any resemblance to real companies is strictly intended; any precise identification with real companies is, I trust, impossible.

Over the past few years, I've had hundreds of designers write to me asking for advice on how to convince management that their companies need to use GD&T properly. The common complaint is that GD&T is used, but little attention is paid to how correct the specifications are. Too often, the people responsible for the specifications do not have the proper skills, and management is reluctant to invest the time and money for training. Some management paradigms are:

At first glance, the investment for training can seem prohibitive, but management needs consider the costs that result from NOT training their employees in the proper application of GD&T. Management needs to take a realistic look at the escalating costs that can result from from poor drawing practices, overly restrictive tolerances, vague specifications, improperly built gages, parts that don't fit, and fixing problems in production that could have been avoided in engineering. These costs cannot be ignored, and when compared to the cost of training, training wins every time.

Last month's article, "A Tale of Two Cultures," compared the way two cultures handled GD&T training. It exposed the poor training practices in the U.S. in comparison to India's extraordinary handling of employee training. This month, we'll take a look at two companies to illustrate the time and expense companies waste due to poor drawing practices.

Case 1: The Oldtyme Axle Component Company
Oldtyme Axle Components has been around for decades and their product line hasn't changed significantly in the last 30-40 years. Oldtyme has expanded operations to several plants in the United States. Oldtyme does not use GD&T on its designs. Let's look at a typical scenario.

Oldtyme moved some of their operations overseas to reduce labor costs. One of the parts they started to outsource was a rear differential case. When the first container of parts came back from the "new" plant they were sent into the testing lab for "assembly and evaluation" (testing to validate the parts). However, it was quickly discovered that the gears could not be assembled into the rear differential case as the cavity was too small.

This case had been manufactured successfully for more than 10 years and you probably know someone with a vehicle using this case. So why did the case come back from the "new" plant as scrap when the "old" plant had been making it for years? The quality department had verified that the parts were "good," and they met the print, so why didn't the parts assemble? It was a real dilemma as the company wanted to start ordering 100,000+ of these rear differential cases per year. Here are the expenses that resulted from this problem:

Not all of this expense was avoidable, but as you will see in the next section of this article, there was a lot of room for cost avoidance/savings. A significant portion of the expense came outside of engineering.

Let's not underestimate the other "costs" of this problem: the negative impact this event had on Oldtyme's customer, the risks to the company's reputation, and a lower employee morale. Because there were always several of these types of problems going on simultaneously, the employees were so stressed and busy putting out fires, they didn't have time to build their skills.

Plus, after all this effort, Oldtyme is still at risk for additional changes that will probably be necessary in the near future because they solved one problem rather than using a system approach to understand the component requirements.

Case 2: The Strategic Axle Component Company
Strategic Axle Components has been around for decades and their product line hasn't changed significantly in the last 30-40 years. Strategic had expanded operations to several plants in the United States. A few years ago, they realized that using GD&T could save them time and money, and they had ETI provide onsite training in fundamentals, advanced concepts, and tolerance stacks to all of their departments.

Strategic moved some of their operations overseas to reduce labor costs. One of the parts they started to outsource was a rear differential case. When the first container of parts came back from the "new" plant they were sent into the testing lab for assembly and evaluation (testing to validate the parts). The gears were assembled into the case perfectly.

Let's look at how GD&T helped this company throughout the product development process:

Total cost for doing the design right the first time was approximately $309,300.
Compared with the cost from the Oldtyme example: $340,100.

This represents a $30,800 savings over the time and money Oldtyme spent fixing a flawed, vague design — and Strategic didn't have to make any embarrassing apologies to their customer.

Remember, this cost includes a one-time GD&T training expense. The additional investment in ensuring that the proper people had the skills for doing the job correctly paid off and will continue to save money each time the skills are used. Next year's savings will be even greater.

Many companies operate like Oldtyme Axle, where they spend much of their effort putting out fires instead of building the necessary skills in their employees to do the job properly. With increasing competition, this method won't work for very long. These companies will not be competitive, won't be able to keep good relations with their customers, and will disappear.

Understanding GD&T is vital to an efficient product development process. The following questions will indicate if understanding GD&T is a problem in your organization:

If you answered yes to three or more of the above questions, your company can benefit from GD&T training.

Take a look at the chart below to see the potential savings GD&T provides at each stage of product development.

As you can see, the benefits of training your employees in GD&T across all departments far outweigh the costs. One drawing error can result in expenses that add up to a waste of time, money, and — when you include warranty issues or product recalls — possibly even your company's reputation.

Some readers may suspect that I padded the numbers to achieve favorable results. I assure you, that is not the case. Actual examples are difficult to find because companies are not willing to air their bad examples. You can create a potential cost savings analysis for your company using the tools described below.

Calculate your potential savings using GD&T correctly
ETI has created a tool to help companies understand how much they can potentially save annually using GD&T. The GD&T Cost Saving Calculator analyzes your company's data and compares your current expenses with an estimate of the potential savings available from training your employees. For more information on this valuable tool, see this month's Tech Tip.

Another valuable tool is the GD&T Skills Survey that your employees can use to measure their existing GD&T skills. For more information on this valuable tool, click here.

Try the cost-saving calculator. Measure your employees' skills. See the benefits of GD&T training. Then, call 800-886-0909 to schedule onsite training for your company. ETI can also provide computer-based and web-based training for your employees.

I work in the aircraft industry. There are many times that a part will have two flat sides and the rest of the part will be contoured. Using ASME Y14.5M 1994, is it allowed to mix datum plane callout with datum targets? Shown below is a crude sketch.

Planar datums, feature of size datums, and datum targets are often used together. For example, a primary datum feature (lets call it "A") described with datum targets must be accompanied by a secondary and tertiary datum reference do be a repeatable datum. Therefore, the primary datum feature may also be referenced as a planar datum (let’s say "B") until a secondary and tertiary datum feature are established.

Just remember that if you specify a datum, it needs to be used (referenced in a feature control frame).

ETI appreciates your questions and comments.
Send your GD&T questions to: ETImailbag.

CALCULATE YOUR POTENTIAL SAVINGS USING GD&T
Businesses need to understand that training expenditures can actually save money in the long run. As this month's article explains, the costs of meetings to discuss drawings, scrap cost, gage rework, — and a company's reputation — can equal many times the cost of GD&T training. This ETImail Techtip takes a look at a valuable new resource for manufacturers.

GD&T Potential Savings Calculator
The GD&T Cost-Saving Calculator is the latest free resource from ETI. The calculator is a tool that helps companies understand the amount of unnecessary expenditures each year due to employees not knowing how to correctly apply and interpret GD&T.

* Creating, interpreting and revising drawings
* Communicating or interpreting design requirements for suppliers and manufacturing
* Manufacturing expenses

Try the Free GD&T Cost-Saving Calculator, Today
The calculator can be used at the company, division, department or project level. It analyzes your data and estimates the annual savings your organization will realize in each aspect of design, inspection, and production. Enter information for whatever scope of analysis you wish to perform. Tool tips provide assistance with understanding data entry.

Even if you estimate conservatively, you'll be amazed at the impact that the correct application of GD&T will have on an organization's ability to cut costs. Try it for yourself. Go to the GD&T Potential Savings Calculator.


	ETImail Feedback Have comments about anything you've read in ETImail? ETI will post your comments here and provide a forum for more discussion about GD&T topics.

Total runout is not a very common specification. In the last issue of ETImail, Alex asked readers for advice about a setup that could be created to check it. We received many good responses. Here are a few:

From Don Jasmann, ES QA and Reliability Engineering Manager
One method for verifying total runout is to conduct the inspection on the machining center that produced the part. The dial indicator is mounted on the cross slide or carriage, the part is rotated and the indicator moved with the machine tool. The dial indicator must contact the part on the backside of the tool path (opposite side of the centerline), otherwise the indicator will always read zero.

Click on drawing for larger view.

The total indicator reading obtained will be twice the actual total runout. The total indicator reading is then divided by two and the result compared to the value in the feature control frame. If the machining center is not "chucking" the part on the appropriate datum, then the actual total runout of the datum must be considered as well. Please see attached for a visual description.

From Rob TerMaat, ATS Automation Tooling Systems Metrology Dept.
Good Day,
We are involved with shaft measurement continuously at our facility and have developed a dedicated fixture which serves perfectly for the chore of obtaining total runout.

Starting with a solid base, we have mounted 2 V-Blocks to support shaft by Journals (Datums). Next we mounted a high precision linear slide to the base for the purpose of holding the indicator. Next the indicator chosen must have a T.I.R. function, the Mitutoyo model 543-262 is what we are using.

As the indicator contact point sits on the shaft. We zero the Indicator, making sure the T.I.R. mode is activated, and begin to spin the shaft with one hand while the other pushes the indicator along the length of the shaft.

When the end of the shaft is reached the indicator will show you the total indicated distance the indicator spindle has traveled, This number we record as total run out.
Hope this helps, we have made an exact duplicate of this gage for our customer and all issues concerning measurement co-relation have since disappeared.

From Roger D. Lawson, TRW Inc
In regards to the question in last month's letter from Walve Nandkumar:
Remember that we use total runout to help control runout and straightness. Measuring total runout is the same as circular runout over the length of the feature.

Holding on the datums and rotating the shaft, start with your indicator set at zero at one extreme (end) and take a circular runout reading and with out resetting zero on the indicator take readings at several location along the length of the feature noting the highest and lowest readings on the indicator. The range of those reading is the total runout.

From Art Kietlinski, Industrial Measurement Tech II
In the shipbuilding industry I worked in a machine shop for 20 years, where we were called upon to do TIR (total indicator runout) checks on all types of shafting. The instrument we relied upon was an engine lathe.

A starrett surface gage, with pins built into the base that can be pushed out so they will ride on the edge of a precision table or slots on a machine table in conjunction with V-blocks can also be used.

The preferred method of choice for me now is 3-D modeling. I use Photogrammetry or Laser tracker systems to model the as-built features of the part for dimensional analysis.

From Dorin Stancu, Interiors AQE - GM Business Unit, Johnson Controls, Inc.
In a previous job at a manufacturer of precision shafts for the automotive industry, we routinely verified total runout (and harmonics, in some cases) using Taylor-Hobson equipment - see http://www.taylor-hobson.com/talyrond290.htm.

P.S. I am not affiliated in any way with this company, I just appreciated their equipment's capabilities and quality of support received from them.

Comments about "Tale of Two Cultures":
Alex,
I could not agree more with your commentary in tale of two cultures:
Rewarding skills that enhance job performance. I forwarded it to a number of my coworkers and friends and they all have echoed the same sentiments. Your article touches the root causes of the decline of American engineering as a profession and output quality.

Communication and Leadership are overly hyped in the U.S. industrial culture. But then, we are seeing a live demo of what happens when communicators don't know much about what they are communicating for and leadership don't know what they are leading! I have developed a quote that I recite when defeated by such situations -- "If you can talk, you don't need to work" --is the rule of success in corporate America!
— Kalrav Buch

The article "A Tale of Two Cultures" was, sadly, very accurate. My current employer, a large manufacturer of industrial equipment, is a case in point. I recently completed a home study course in tolerance stacks, which I took at my own expense. When my boss found me at my desk doing a tolerance stack on a design I was working on, he told me I was “wasting time”. Now I hide in the cafeteria when I need to do a stack.

The cost of this kind of management behavior to a company goes beyond poor designs and high warranty costs. Ultimately, the most competent engineers and designers will become frustrated and leave. I have seen many of my best colleagues quit, and I am only still here because I am looking for another position in a very specific geographic
region. — Name withheld upon request.

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