Becoming Certified in GD&T
I wrote about this a long time ago, but it’s worth mentioning again as the new year approaches (for people who still do New Year’s resolutions!). Regular GD&T users should be aware of the certification process for GD&T Professionals.
The American Society of Mechanical Engineers (ASME) has established a credential for GD&T proficiency, called GDTP, which stands for “Geometric Dimensioning and Tolerancing Professional.”
It is a testing process that measures your ability to interpret and apply tolerances correctly. It is not a license to practice GD&T (no one can legislate that) but it is something that looks nice on your resume!
There are actually two certification levels: the Technologist Level, which measures your ability to read GD&T; and the Senior Level, which tests not only interpretation, but also the application of GD&T to a design. One does not necessarily need to become a Technologist first; some people go right for the Senior Level, although they are required to document at least five years of experience in GD&T (and they have a more difficult test!).
If you decide to pursue either level, be aware that the questions on the test come from all sections of the 1994 Y14.5 standard. (Despite the new 2009 edition, as of now the testing is on the 1994 standard.) Each chapter has a “weight” that determines the number of questions from the chapter that appear on the test. This means that there is more than just GD&T; you need to be familiar with the nuances of traditional tolerancing as well as the many definitions contained in that standard. Some questions representative of the Technologist Level:
Sample question #1:
A dimension “not to scale” is symbolized by:
a. placing the number in parentheses
b. placing a line under the number
c. including NTS after the number
d. italicizing the number
Sample question #2:
If a datum feature of size is applied RFS, a datum displacement is:
a. not allowed
b. allowed at MMC
c. allowed at LMC
d. allowed at the resultant condition
Sample question #3:
When applied to planar surfaces, angularity, parallelism, and perpendicularity also control:
a. size
b. location
c. form
d. Rule #1
Sample question #4:
Which of the following datum feature symbols is incorrect?
The GDTP process is not for everybody, but if it’s something that might interest you, contact us for some guidance or you may visit ASME’s website for more detail:
http://www.asme.org/Codes/CertifAccred/Personnel/Y145_Geometric_Dimensioning.cfm
FYI — the answers are: b, a, c, and “Q,” respectively. If you got all those, send a comment and I’ll post some questions from the Senior-level test next time!