Measurement Methods: Functional vs. Variable. FUNCTIONAL GAGING (Attribute or Hard Gaging)

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1 Page 1 of 5 EffectiveTraining Inc., Westland MI, Volume 01: Issue 4 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. ETImail is now available in PDF format. To read the PDF file, you will need Adobe Acrobat Reader. Known as the "Doctor of Dimensioning," Alex Krulikowski is a noted educator, author, and expert on Geometric Dimensioning and Tolerancing (GD&T). A design manager with one of the world's largest manufacturing corporations, he has more than 30 years of industrial experience putting GD&T to practical use on the shop floor. Measurement Methods: Functional vs. Variable Alex Krulikowski When selecting inspection methods for product evaluation, a choice must be made between dedicated functional gaging vs. flexible variable measurement using a CMM or open set-up. This comparison highlights differences that exist between the two. FUNCTIONAL GAGING (Attribute or Hard Gaging) Gage checks size, Rule #1, location, and/or orientation of entire part feature. Capable of checking multiple part features simultaneously. Provides a pass/fail answer for a part feature tolerance specification. VARIABLE MEASUREMENT (CMM or Surface Plate Layout) Checks X,Y, Z coordinates (at probe contact points only). Checks size independent of location. Manual or software estimates used for Rule #1 and effects of maximum material condition. Provides variable data for a measurement. Web Highlights Good Parts, Good Measurements A machine tool must be capable of generating both, says a software company with a new vision for the role of metrology data in the emerging era of globally integrated manufacturing enterprises. Article by Mark Albert in Modern Machine Shop Online. 1. Ideal for functional "fitness for use" inspection. Gage acts as worst-case mating part. 2. Fast and easy to use. Minimal training required. Little judgment required making pass/fail decision. 3. Machine operators or auditors can do the inspection near the production line, reducing moving and wait time. 4. Gage tolerances may be biased to eliminate user's risk. 5. Easily relocated (portable). 6. Can produce quick results for process control (variable gaging) or product acceptance (functional gaging). 1. Cost of gage and lead-time required. 2. Not flexible--changes take time and may be costly. 3. Attributes gaging or functional gaging provides little or no information usable for process adjustments or 1. Provides information or machine/process adjustment and capability analysis. 2. Avoids costly dedicated gages. 3. Easily accommodates changes. 4. Less operator (human feel) sensitive. 5. Easy to get data on additional features if requested. (Not limited to features built into the gage.) 1. RFS inspection does not assure functional product. Translation to MMC provides only an estimate of virtual conditions. 2. Checks at probe points only--may not detect local variation, form error, or orientation error that could destroy

2 Page 2 of 5 Inspection Time Reduced Read about quality technicians who must work with tolerances as small as millimeters in this article from the October 2001, Quality Online E- zine. capability analysis. 4. Each gage requires periodic maintenance and/or calibration. 5. More operator sensitive in some cases. 6. Gage may become obsolete if part is changed or discontinued. 7. Gage tolerances reduce manufacturing tolerances. "fitness for use." 3. Requires high-cost equipment and highly trained personnel. 4. Measurement uncertainty (error) is difficult to quantify and bias to reduce user's risk. 5. Discrepancies between inspection sources are difficult to avoid and resolve. 6. Higher costs for programming and operation. 7. Can take hours or days to get results. 8. Operator developed programming or software may differ from other operators or established standards. ETI Products Self-Study Workbook This start-to-finish selftraining course in geometric dimensioning and tolerancing has become a classic in the field. Learn GD&T at your own pace, using problems from real life applications. Thirty targeted lessons give you an insider's grasp of GD&T. ETI Services 1. For quick verification of "fitness for use" on higher volume or expensive parts. 2. For verification of higher risk parts and characteristics. 3. Typical applications would address hole patterns, critical features, irregular forms, location, and orientation, and "fit" characteristics. 4. For parts that will be offered as individual service components. Because parts must mate with customers' components regardless of age, source or condition, receiver gages are recommended. 5. Preferred when measurement uncertainty must be minimized. 6. When roundness or straightness variation is present: (form variation can cause "measured size" to differ from "effective size" and adversely affect fit within mating parts). 7. When bend, twist, bow, warp, or other distortion is present. (Fit and function are affected by maximum material and virtual conditions; these may be impossible to properly check with variable measurement methods.) Plastic parts, multilevel stampings, and subassemblies of moving parts are examples of products that are difficult to check properly by other means. 1. For initial sample analysis, product/product development and capability analysis* 2. For low volume or short-lived products* 3. When quick answers are needed and no gage is available. 4. For low-risk measurements or proven capable processes requiring infrequent sampling, where form or orientation error is insignificant. 5. For adjustment, debugging and troubleshooting of equipment and processes. 6. For process control. 7. For positional measurements at RFS. * May need separate form measurement and analysis requiring cumbersome and/or uncertain translation of RFS data to estimate MMC and virtual condition relationships. ETI Offers On-Site Training Find out more about what ETI has to offer your organization. Click here Consideration of the advantages and disadvantages suggests that each approach has its place, and at times both might be needed. It is important to recognize that the results obtained from one method may not agree with the other. In any case, the functional evaluation must govern the acceptance of the product. We welcome your feedback. Send comments about this article to ETImailbag. Your opinions will be posted in the next issue.

3 Page 3 of 5 Tech Calendar Standards in the News ETImail's Standards in the News takes a look at real-life issues where standards have failed or need improvement. This month: lack of standards hinders e-business supply chain automation. Excerpts from Computerworld online ezine. Stay up to date on the latest industry news with the ETI Tech Calendar.Click here Quality Quote LACK OF STANDARDS BLOCKS SUPPLY CHAIN AUTOMATION New Orleans -- A lack of standards has become a huge barrier to using e-business technology to automate corporate supply chains, and there currently is no real solution in sight. A number of corporate users expressed doubts that any initiatives will produce standards that meet with widespread acceptance. And until that happens, they said, companies trying to automate their supply chains will have to continue relying on a jumble of different technologies and communications channels. The current lack of business-to-business standards is the single greatest barrier to implementing Web-based supply-chain systems for many large users, according to Scott Stephens, chief technology office at Pittsburg-based Supply Chain Inc. Creation of common e-business definitions and data formatting techniques were touted as being of "paramount" importance. "It's a huge problem in some industries," Stephens said. Full story Quality improvement will result from people improving their processes and management improving the system. --Thomas Pyzdek, from Pyzdek's Guide to SPC: Applications and Special Topics, 1992 ETI Staff President Alex Krulikowski Product Development Jamy Krulikowski Excerpted from the article, "Lack of Standards Blocks Supply Chain Automation" by Marc L. Songini in Computerworld, April 5, The ETI Mailbag I have a question about bonus tolerance. Could you let me know the table of bonus tolerance in the case of LMC just like in the case of MMC in the Fundamentals of Geometric Dimensioning and Tolerancing textbook? Whenever I teach the course to my students, they ask me similar questions; however, I cannot make that table. Please explain it. When the LMC modifier is used in the tolerance portion of a feature control frame, a bonus tolerance is permissible. In the case of LMC, bonus tolerance works just the opposite of bonus tolerance with MMC. The chart compares bonus tolerance with MMC to bonus tolerance with LMC. Programming Cindi Rowe Jim Todd Nathaniel Kraft Sales Kathy Darfler Nancy Davis Internet Services Brandon Billings Also, on page 257 in the Fundamentals of GD&T, 2nd Edition, textbook, Figure 9-7 shows a chart with bonus tolerance at LMC. If you have any further questions, please let me know.

4 Page 4 of 5 Graphic Artist Matthew Pride Writer/Editor Katherine Palmer Order Processing Tina White Shipping Gary Walls Receptionist Lindsay Carlington From teaching ideas to new products that will assist you in training or on the job, the ETImail Tech Tip will keep you informed about new technology and ideas. This month's Tech Tip tells which dimensioning habits to avoid. THE TEN WORSE DIMENSIONING HABITS Send your GD&T questions to: ETImailbag. Alex's Tech Tip 1. Dimensioning the part without understanding how it functions in the system 2. Using coordinate dimensioning instead of GD&T 3. Using RFS when MMC or LMC would work 4. Arbitrarily using the outside or convenient surfaces of the part as datum features 5. Copying tolerances from similar production parts 6. Labeling centerlines as datums 7. Use of restrictive general or titleblock tolerances without using more generous tolerances where possible 8. Requiring the drawing user to make assumptions 9. Applying GD&T and datums last to the part 10. Not controlling all features on a part (for size, location, orientation, and form) If you know about a new tech tool or an innovative idea that would aid our readers, please write us: ETImailbag. 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. Question about ETImail Archives: I find the ETI Newsletter very informative and was wondering if there is a way to access the prior issues. Thanks, Erroll W. Green Mr. Green, Glad to hear you are enjoying ETImail. Since we now have 3 back issues, our website administrator has created an archives section on the home page of our website, etinews.com. To access previous issues of ETImail, simply click on the link in the left menu column, under ETI, then ETInews. There you will find the current issue, the archives, and an option to subscribe to ETImail. ETI would like to hear from you. If you have an opinion about any ETImail article or feature, please write to our ETImailbag. We would appreciate it if you'd keep us in mind when you need GD&T training, consulting, or GD&T products. Feel free to contact us by or by phone at or

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