Economics / Cost of Applying GD&T

[gioiosa]

Does anyone know of any reference material that discusses the associated inspection cost of adding GD&T to drawings?

I have often heard that applying GD&T to drawings can blow up the cost of a design, but I have never seen any info on the associated costs and I am looking for general guidelines on producing drawings that apply GD&T in the most economical way.
There are many ways to dimension a drawing with GD&T and achieve the desired design intent, but I want to make sure I am producing drawings/designs that are cost effective for both the manufacturing and inspection processes.

In general, I suppose I'd be looking for the following types of info:

1. Cost effective datum setups
2. Cost of inspecting certain types of features (profiles/location/flatness etc.)
3. Inspection cost vs Tolerance tightness

[Kelly_Bramble]

Does anyone know of any reference material that discusses the associated inspection cost of adding GD&T to drawings?

More often than not, PROPER application of ASME Y14.5 GD&T decreases the overall cost of part production. Inspection requires the metrology folks to establish an origin, when there are not datums specified the inspector has to estimate which feature is an origin to inspect specified features. Specified datums eliminate that arbitrary process.

The point of inspection to ensure the part meets specification and the point of specification to ensure the part works in the target assembly or application. Parts that are inadequately specified and inspected may simply not work, thus wasted money and time.

I have often heard that applying GD&T to drawings can blow up the cost of a design, but I have never seen any info on the associated costs and I am looking for general guidelines on producing drawings that apply GD&T in the most economical way.

"blow up the cost of design"? Doing my best to be polite, but not if the designer knows what they are doing. Placing nonsense on an engineering drawing creates confusion for everybody, manufacturing, inspection and a part that may or may not work the first time.

The facts are that the GD&T standards used in industry are the ONLY dimensioning and tolerancing standard we have. Seriously, keep in mind that the GD&T standard includes limit type dimensioning.

There are many ways to dimension a drawing with GD&T and achieve the desired design intent, but I want to make sure I am producing drawings/designs that are cost effective for both the manufacturing and inspection processes.

Not really, assuming you and your organization does not use self-invented dimensioning and tolerancing. Look, the reason for a dimensioning and tolerancing standard to so everybody speaks the same language. Non-standard practices create confusion particularly when sending the design out to new suppliers and manufacturing organizations.

In general, I suppose I'd be looking for the following types of info:

1. Cost effective datum setups
2. Cost of inspecting certain types of features (profiles/location/flatness etc.)
3. Inspection cost vs Tolerance tightness

Answers:

#1 - minimal if not free
#2 - 99.9999% of the time - Cheaper than a non-function part making it to assembly minimal with proper equipment (1 – minutes max for very-very complicated part).
#3 - Free, with the proper inspection equipment.


The most significant problem I’ve seen in hundreds of companies I’ve trained at and reviewed their engineering drawings all across the world is over specification of tolerances and or placing nonsense on the drawings. This is not a GD&T problem but a designer or engineer that does not know what the functional requirements are or the target manufacturing process capabilities is as well as just not being knowledgeable in proper design.
See the following for more information
https://www.engineersedge.com/traini..._tolerance.htm

[Cragyon]

No knowledge of GD&T = Drafter

Applicable knowledge of GD&T including when to use the geometric symbols and not = Designer and above.

Unless you're drafting very low end hardware, like wood things and stuff.

[jboggs]

Speaking for myself, and based on my 45 years of experience, GD&T is just a tool, among many, that engineers use to communicate their thoughts to others in a three dimensional form. And just like any tool, it is effective if used properly and ineffective, or even harmful, if used improperly. I can understand a young engineer hearing things from the old hands about GD&T, or any other tool they don't fully understand, and taking their negative words to heart. A couple examples: I once had a client that refused to accept any drawings done on CAD because in his words "anything done with that CAD sh__ is wrong." It took time but I convinced him that SOME CAD drawings might be right, depending on who makes them. Another example from my experience: if the personnel in the fabrication shop you're dealing with haven't been trained and don't understand all those strange symbols, they will automatically raise their price tying to cover their butt. The moral of the story is this: any tool you use to communicate must be properly understood both by you and by those to whom you are communicating. That includes machinists, inspectors, end users, purchasing, management, and any other party that is expected to glean information from the drawing.

It is your job to make sure that your expressed intent is perfectly clear, simple, unambiguous, and cannot be misinterpreted. To do this, you must consider your audience, and how they will interpret your information. Putting corporate rules and guidelines aside for a moment, if the users of your drawings will understand your GD&T expressions clearly and correctly, use them. If not, don't.