Operational Dimension Drawing By John R. Holsen

1. Operational Dimension DrawingBy John R. Holsen This presentation explains Traditional, Geometric, and Operational Drawing Tolerance Systems

2. Advantages of This New StandardODD- 2011 to present • ● Replaces revisions only with Version(s) • ● Integrates Traditionalprecision centric method with - WWII era accuracy centric Geometric Methods with Coordinate Grid. Called GD&T • ● Pairs ‘features’ with ‘profiles’ and their relative importance to other groups in a single Data Reference Frame (DRF)

3. Traditional Dimension Accuracy than the average location of more circles or cylinders to any required distances to profiles (edges) N=5 circles or cylinders measures less accurate BUT it reports as LESS PRECISE because laws of probability dictate the worst location of all to the center is less precise than only 5 Large deviations are often ‘simulation error events’ in machine code programs..

4. 1940 GDT 1960’s first used in industry 1955 first Statistics possible CAD Geometric Dimensioning and Tolerance (GDT) was born in 1940, at the height of World War II. Statistical variation metrics would not be invented for another 15 years and quick assembly of parts was a problem under traditional tolerances. Thick plate steel added to the difficulty in understanding what the design assumed, called the Underlying Engineering Assumptions that allowed setup of machine tools or hole patterns that may have nothing to do with edges, the traditional starting point, or the edge of a parts, which varied with stamping pressures or casting roughness and maximum versus minimum hole conditions. Is the part 3.000 +/-.003 ????? Stacked Tolerance ‘hinges’ parts 1.000+/-.001 1.000+/-.001 1.000 +/-.001 Does the hole pattern or the sizes or both Need to be held ‘Best’? In effect Or is it Best Fit or Not At the time, no expectation about variability was possible to calculate

5. The Geometric Tolerances avoid the formality of tying the features todatums(the three plane surfaces) All coordinate measurement that encorperatesa complete design entity or Piece Part requires a Data Reference Frame. It is a zero zerozero point and three perfect planes at right angles to each other. But there is never any absolutely perfect intersection of lines or planes on a piece part. A precisionflat surface simulates it, or else the machine’s flat stage simulates a reference plane. Both systems are After the 50 year old underlying engineering assumption in traditional dimensions :that roughness dominates positional errors.

6. GDT loves a hole which is simulated with a pin guageThis pin used in manufacturing then simulates the second Datum ‘B’ in any of several ways – by assumption that 1) the pin is at 90 degrees to a plane at the part surface or 2) Profile or edge finding at high points of fit for GDT Pin or Line from 2 Points

7. GDT edge versus Traditional Edge Assumption during DRF definition Geometric Dimensioning Traditional Dimensioning • Maximum Material ● (Averaged) 2 point random hits near ends

8. Traditional edges methods find degraded lead-in and lead out artifacts from machine tools near the head and tails or shrinkage of casting processes or plastics post mold shrinkages. Geometric Dimensioning Traditional Dimensioning • Imperfect Material • At MMC magnifies • Pin placement • ERROR ● Using ONLY 2 point random hits near ends Y DRF 0,0,0 Y Y ’ Guage Pin Cocked fit Into Datum B hole X Z Simulated Datum ‘A’ plane from fixture setup Z X

9. If you believe Wikipedia, “Geometric Dimensioning And Tolerances Are Not Used in Manufacturing”. The part drawing does not anticipate manufacturing process variables. Some processes are too setup intensive to use the “Datums” as their Actual planes to place the part either level or rotated into a machine. International Standards (ISO) has also declared that all older ‘revisions’ of a drawing MUST be destroyed. This limits the DRFs than could ever be maintained in a drawing system for any piece part. Much of these mandates are obsoleted by today’s demands for such things as optics placed into a profile of a cell phone bezel which requires prior information.

10. Just As a drawing, these days, is likely to have Layers, because it is kept on a computer, the Statistical ability to parametrically recall the characteristic shape and location of a profile exits and can be used to do operational callouts. By Overlay of Average Prior Profile Information and offline CMM / Cad Data

11. PCDMISOFFLINE.COM and OFFLINEPCDMIS.COM are two web pages I have begun to try to facilitate such change. I have had a life of many coordinate measurement contracts in an area of the USA (Southern Wisconsin, Northern Illinois) that has the most machine tool population of any area in the USA. I cannot list all the shorter jobs I have done, but let me say that I know there are better ways than the often seen fixture building industry that grows up around the failure of aging drawing systems to keep up with modern requirements for more valid data in both first article or model tooling and part production as well as the more traditional application for Coordinate Measuring Machines – high volume repeated production runs. - John R. Holsen 920-850-0920

12. Below is a quick preview of the newer style drawings already finding popularity, I only am following through with a more complete drawing standard philosophy The Operational Method uses Less Clutter Position Stacking or Grouping Center Deviation tolerances is 3.0 X Sq Root of added feature Std. Deviations from SPC file . Setup - use previous OK profile and laser or camera assisted alignment. Finish Profile To hole Centerline 1-5/16” All Dimension +/- .002 this layer 4.50” 2.50” 1.25” 3.00”