How Much Is GD&T Used These Days?

Your boss is pushing for GD&T? What in the world have you been using, henway in lieu of inches? A duckdo instead of a centerline?

GD&T is a fine thing. If your designers know how to use it and your inspectors know how to use it as an inspection tool.

It allows important features to be defined in such a way that mating parts can be used that would not be acceptable if dimensioned by coordinates.

For single part assemblies, the advantages are not so great.

GD&T stands for?

(Feeling like an idiot)

http://en.wikipedia.org/wiki/Geometric_dimensioning_and_tolerancing

Thanks.

It has been about 40 years since I did my engineering drafting courses. The general principles where drilled into us, along with the "cost" of dimensioning parts too tightly.

I remember one grad student that dimensioned mechanical parts with zero tolerances. The machinist would sit down and try to explain to him it would not work, and the student would only argue. After about the third time the machinist (with the grad students supervisors approval) machined the parts as close as he could to the zero tolerance - the cost was exorbitant and blew the grad students budget.

The grad student was really upset when the parts would not fit together - a 1.0000 inch shaft would not "slide" into a 1.0000 inch hole.

We were all happy when the student was excused from the program.

Hi, Just32:

Having a lifetime of engineering drawing practice, I can testify to the necessity for GD&T. In answer to your Q: I do not know how many people use them but since there exists many standards documentation, e.g. BS 8888, it may be used by hundreds of thousands of draughtsman and modellers...

Anyway, try this:

http://mtm-inc.com/reduce_project_risk/geometric_dimensioning_and_tolerancing/

In addition to what has already been said, GD&T should help reduce machine time and costs on features that are not critical as well as indicate to the machinist what features need more precise processes such as grinding or honing instead of using a rough face mill or drill. If machined to specifications the mating parts will always fit and function. GD&T will also let quality know which parts are usable and when to call engineering for non-conforming parts.

I would also suggest to you to review your drawings and their functions to reduce the decimal places where ever possible. You don't mention whether the dimensions are given as inch or metric but that your tolerances are 3 & 4 places. These tighter tolerance features would benefit everyone to have GD&T properly applied with them when practical.

Actually most of our designs could be dimensioned with fractions, nearest 1/16", but too many of the group, boss included, get hung up on the fact we are an "engineering group" so should be "precise". Than sent them to be built by the cheapest shop we can find, sometimes even Mexico. Of the vendors we use most do not use GD&T and the ones who do say it adds cost. It appears to me that like all tools there are times to use them and times not to use them.

Remind your boss that zeros to the right of the decimal point are free only to the designer. Every zero to the right of the decimal point adds cost in manufacturing complexity, inspection and unnecessary scrap and rework.

Don't even go the GD&T route unless the company is willing to train everyone who has a need to read and interpret a drawing for any reason whatsoever.

I've used it in several jobs over the years and can appreciate the tolerancing ambiguities that it addresses and fixes, but it can also create great chaos if people don't know how or choose not to understand it.

For example, the aerospace company I currently work for would benefit greatly but the family management prefers the blacksmithing methodology they've used for the last 30 years or so. (no insult intended to the fine art of blacksmithing )

Hooker

Generally speaking everyone doing mechanical design is using the ANSI Y14.5B standard which is GD&T.

What everyone is not doing is properly applying the standard for the most cost effective result. The standard does NOT require every feature be defined with basic dimensions and feature control frames when x-y fractional coordinates will do. Of course, you could apply the same tolerance with the basic dim and frame if you wanted to. (Apologies to those who might not know the jargon!)

You could tell your boss you are using the PRECISE dimension and tolerance needed to produce a functional part at the best cost.