The February 21, 2018 meeting of the New Mexico SolidWorks User Group was held at The BioScience Center in Albuquerque, 5901 Indian School Road NE, Albuquerque, NM.
Good eats from Monroe’s New Mexican restaurant was provided by our sponsors. We had vegetarian enchiladas with mild green (chile), chicken enchiladas with red (chile), chicken enchiladas with green, warm flour tortillas that were only a few hours old, refritos frijoles (beans), arroz (rice) and of course, biscochitos (cookies). By the end of the meeting it was all gone. [Good to get back to our New Mexican cuisine after those SlugMe pizzas]
We had 40 people in attendance including one from Las Cruces, NM (3 hours south).
- 5:30 - 6:00 Arrive, Get Some Food, Meet Someone New
- 6:00 - 7:00 Specifying GD&T for Mechanical Part Definition (Part 1)
- Bob Goodwin (Sandia)
- 7:00 - 7:15 Break
- 7:15 - 8:15 Specifying GD&T for Mechanical Part Definition (Part 2)
- 8:15 - 8:30 Wrap Up / Prizes / Giveaways
CONGRATULATIONS TO OUR LONG TIME MEMBER AND REGULAR ATTENDEE FROM THE EARLY DAYS, DAVID SAMUEL. David attended this years BEYA (Black Engineer of the Year) STEM Conference, February 8-10, 2018, in Washington D.C. where he received the Dr. William R. Wiley Legacy Award. David was one of thirty-two distinguished engineers to receive awards this year. And if that wasn't enough, a few days later, David retired from Sandia National Labs after --- I think he said 40 years; at any rate, a long time. David, best of luck and know your warm smile is always welcome at NMSUG.
The November SlugMe presentation is available on You Tube. Search, SlugMe 2017. If you weren't able to attend the SolidWorks Largest User Group Meeting Ever, hosted by Todd Blacksher, it is well worth your time to view the video. It was a plethora of SolidWorks Tips and Trick's presented in short 1-2 minute vignettes, one right after the other. Todd is a great presenter and you are guaranteed to see at least a few things you could use in your day-to-day SolidWorks workflow.
Geometric Dimensioning and Tolerancing - Overview
Geometric Dimensioning and Tolerancing is a language for defining and communicating the geometric properties of mechanical parts (e.g. ASME Y14.5). The language can be applied to both 2D drawings and 3D models, and is a significant improvement over "plus and minus" tolerances. Like any language though, getting started can be difficult. This presentation will help to lay a foundation for further study as well as provide examples of what "good GD&T" looks like.
The mantra of the NMSUG is: "Life is about Relationships. Relationships are about Communication. SOLIDWORKS is a Communication tool." Join us for this special event to learn some of the grammar in the language of SOLIDWORKS.
Specifying GD&T for Mechanical Part Definition
The intent of the presentation is to provide an overview of the concepts and application of the geometric controls most commonly used for machined-part definition (which includes most of the controls available) without going into the fundamental nuts & bolts of a basic GD&T class. Basic concepts will be presented as they apply to the particular geometric control being addressed. The most emphasis will be on the True Position control and its variations, from positioning holes, positioning surfaces or median planes, to composite position control. The Profile control, which is the next most useful control, and then the application of the Form, Orientation, and Runout controls will also be described. The philosophy of functional dimensioning & tolerancing, and datum selection, as the basis for repeatable verification of manufactured parts will also be emphasized.
Bob Goodwin currently works in the Mechanical Design & Drafting Services organization at Sandia National Laboratories. He was recruited into the machine shop apprenticeship program, as an inspector, at Sandia in 2003 from the TVI (now CNM) Machine Tool Technology Program. After a year and a half he transferred to the Sandia Design Services organization, and also completed the Design Drafting Engineering Technology Program at CNM – though his best practical drafting training was through 2 ½ years of on-the-board classes in high school. Prior to working at Sandia, Bob worked as a Journeyman Electrician for 4 years, and then as a general and electrical contractor for 12 more. Bob has been doing mechanical design and drafting work at Sandia since 2004. He currently holds a GD&T Professional certification at the Senior level from ASME.
Specifying GD&T for Mechanical Part Definition-Part 1
A search for GD&T yields 2100 hits at the Quality Magazine website (www.qualitymag.com), demonstrating that interest in GD&T is at a high level in recent years.
There are efforts underway to automate GD&T for Model-Based Definition, and for metrology software to run Coordinate Measuring Machines (CMM’s) and other metrology equipment.
“GD&T is so complex, that much of the “code” is dangerously “decorative”, not function-based, and rife with syntax errors which users therefore have no alternative but to “interpret.”” Quote from Bill Tandler, of Multi-Metrics, Inc., and GD&T author, 1 June 2017
Tandler and his colleagues think that 85-90% of GD&T on drawings is incorrectly applied.
- Hard to understand and learn
- Difficult to apply correctly
- Difficult to interpret—especially if applied incorrectly
- Is not fully defined in the standards, or currently cannot yet be codified sufficiently to be automated
- In turn, this is probably one reason for the delay of MBEngineering (MBDefinition)
There is a push to “clean up” the standards.
WHAT IS GD&T? Here are several definitions
- Geometric Dimensiong & Tolerancing is an international system used on engineering drawings to accurately (more fully) define a part.
- It is a well-defined set of rules, symbols, definitions & conventions (noted GD&T guru, Alex Krulikowski)
- Or…concepts, tools, rules, processes & best practices (noted GD&T guru Bill Tandler)
- GD&T allows complete definition and eliminates dependence on “Tribal Knowledge” interpretation of part definition
- A Graphical language to describe size, form, orientation, & location of part features, that is also backed by a mathematical basis in ASME Y14.5.1.
- Embodies a design philosophy called “functional dimensioning”. A part is defined based on how it functions in the assembly or mechanism for which it is intended.
- GD&T is the only tool that imposes truly functional limits of imperfection on machine part features and actually guarantee assembly and operation prior to drawing release
- Early drawings were generally assembly drawings, or sketches, and had no dimensions
- All work was done under one roof by a master craftsman and his apprentices
- File & fit was the standard practice (early gun making, or clock making, etc.)
- No such thing as , or no concept of, “variation”
- Measurement technology was crude
- Every product was hand-made and unique
- Improved measurement technology dispelled the “myth of perfection” and variation is now understood to be unavoidable
- Assembly lines could not accommodate file & fit – highly-skilled labor
- Drawings became the logical place to communicate “tolerance”
- Standards for drawing practice were first introduced in the early 20th century.
- The 1935 drafting standard had 18 pages: 5 pages on dimensioning, 2 pages on tolerancing, the plus/minus system of tolerancing became standardized
- WWII manufacturing exposed the weakness of the Coordinate Tolerancing System, as fabrication of piece-parts had to be subcontracted to outside shops
- Lore has it that Stanley Parker at the Royal Torpedo Factory developed GD&T after a rejected batch of parts actually turned out to be functionally good.
- The British, car companies (Chevrolet) and the US military were the early adopters and publishers of standards prior to ASME standards.
- MIL-STD’s, the ASA, ANSI, and then ASME refined the dimensioning standard into the current ASME Y14.5-2009
GD&T is perfecting existing tolerance schemes. It fills the gaps in the coordinate tolerancing method to allow more complete part definition.
In GD&T the dimensioning schemes are logical, variable, repeatable, and unambiguous. Tolerance zones are variable, based on the material condition of the feature.
In industry, think that the drawing you are creating is for the inspector (NOT so much for the machinist), and you want to convey design intent.
- You are specifying a repeatable methodology for verifying (inspecting) your part
- You are actually specifying how to build a gage to verify a part
- Datum reference frame = Datum Simulator
- Datum Simulator = gage = CMM = etc
- Ironically, you must return to considering perfect parts, or features.
- with CAD, we already model perfect features – CAD models are theoretically perfect
- A Basic dimension is theoretically an exact dimension. [put a box around it.]
Datum – described differently in 1994 and 2009, datums are theoretical constructs-plane, axes and points. It is NOT a feature of the part. It is the granite plate or surface that the part sets upon while mating/measuring. Datums are more closely associated to the gage or to the assembly interfaces that the part must mate to. Datums convey design intent.
DRF-is a datum reference frame: Three planes, three axes, origin point…which describes six degrees of freedom (6 DOF).
FOS-feature of size: hole or boss, or 2 opposed planar surfaces, as opposed to a feature which is a flat surface.
Order of datum specification (Datum rotation) in the feature control frame is important.
A part can have secondary, or tertiary, etc. DRF’s (Datum Reference Frames), which must be related to the primary DRF.
Specifying GD&T for Mechanical Part Definition-Part 2
Material Condition – a key element of the GD&T concept, derived from the conventional concept of “Worst-case condition”
Today it is codified as
MMC – Maximum Material Condition (smallest hole, largest pin)
LMC – Least Material Condition (least amount of material-largest hole, smallest pin)
RFS – Regardless of Feature Size
Understanding material condition leads to concepts like “Bonus Tolerance”, virtual condition, hard gauge definition, reliable location of features in-assembly, protection of wall thickness, etc.
New concepts in the 2009 dimensioning standard:
MMB – Maximum Material Boundary
LMB – Least Material Boundary
RMB – Regardless of Material Boundary
APPLICATION of GD&T
- Choose a Primary Datum Reference Frame (DRF)
- Most important step
- Specifies how to (repeatably) set up the part for verification
- Must convey design intent
- Derived from next assembly interfaces (Functional Datum Selection)
USING GD&T – Application
- Several different examples of Datum Reference Frames set up on example parts were shown and discussed.
- Datum features: i.e. surfaces
- Datum features of size: i.e. holes and pins (axes), patterns of holes, (planes & axes), planar features of size (median planes)
- Compound datums: offset planar surfaces, separated shafts, or shafts of differing diameters
This was the first time in recent memory we had a presentation topic which was so vast that it consumed the entire meeting. (Usually we have two presenters and two topics.) Based on the attendance, GD&T is clearly on the radar of NMSUG attendees. Several members at our meeting acknowledged that they would like to learn and better understand GD&T to both enhance their career and comply with GD&T requirements as they arise in their jobs. In addition to our presenter, we had two attendees with GD&T certifications.
GD&T is a difficult concept that is still evolving. While it may not be prevalent in every engineer’s day-to-day workflow, one only needs to explore the many cost-based course-offerings, seminars, online classes, and books as evidence that it is coming. A two-hour user group meeting is just enough time to provide some history, lay a foundation and grab the attendees’ attention with some simple examples. Bob was particularly effective because of his experience as a part inspector, checking parts against GD&T drawing information.
Every NMSUG presenter receives a certificate of presentation. This one was well-earned. Thank you Bob Goodwin for taking on a difficult topic and executing an organized presentation.
There are two GD&T certification exams
GDTP – 1994 or 2009 Technologist level
GDTP – 1994 or 2009 Senior level
Specific information regarding the exams may be found at www.asme.org.
GD&T: Application and Interpretation, by Bruce A. Wilson
GEOTOL Pro: A Practical Guide to Geometric Tolerancing Per ASME Y14.5-Workbook 2009, by Al Neumann and Scott Neumann
Several titles by noted author Alex Krulikowski
ASME Y14.5 Dimensioning and Tolerancing 2009: Engineering Drawing and Related Documentation Practices ($300.00 on Amazon, $200.00 from ASME)
There are two standards (1994 and 2009) and two test levels for each standard
www.tec-ease.com, online training site for GD&T with both free and premium training tools
NEXT MEETING is Wednesday, April 11, topic TBD
CLOSING AND GIVEAWAYS including a drone, a robot, backpacks, shirts, mousepads, mice, pens, steno pads, coasters…thank you to all our sponsors