IIGDT World International Institute of
Geometric Dimensioning & Tolerancing

for Integrating Standardized Tolerancing Methodologies
Dr. Greg Hetland, June 1995

Even though dimensioning and tolerancing standards have been used throughout the world for many years, much of the doubt/hesitation to fully integrate these standards has been focused around the benefit of utilizing one practice over another for standardization of tolerancing methodologies. The primary difference is between the older linear dimensioning practices and the newer geometric dimensioning and tolerancing practices.


Worldwide standardization of dimensioning and tolerancing practices has been hindered by paradigms that have been and continue to be difficult to overcome. A few of the more common paradigms continually mentioned by students, as well as general management, follow:

  Older prints are easier to understand
  Older prints define design intent better
  Older prints contain all the required information
  GD&T is only required for critical features
  GD&T increases the overall cost
  GD&T is hard to understand
  Profile is hard to use
  Profile cannot be measured

Current Problem

The day-to-day problem is that engineering drawings do not clearly reflect design intent and significant differences exist between drawing packages, which impact product standardization, as well as individual drawing and feature interpretation due to multiple methods of attempting to specify the same thing in different ways. Design intent is considered a set of technical documentation defining the physical and functional characteristics of an item. Physical Characteristics are the geometric parameters of a configured item such as length, width, thickness, etc., while Functional Characteristics include all performance parameters such as range, speed, lethality, reliability, maintainability and safety.

Industry has been faced with the primary burden of training their employees in the engineering language of dimensioning and tolerancing principles. In most cases, universities, technical colleges, trade schools, etc., do not have programs built into their technical programs to teach students the fundamental principles associated with this international engineering language on dimensioning and tolerancing. Even fewer teach advanced principles dealing with applications and analysis.

Additionally, seminars have existed for years, directed by consultants with tremendous differences in technical depth of knowledge on this subject. Based on these differences, students leave these one to five-day seminars and are expected by their employers to have the fundamental knowledge to work proficiently on a day-to-day basis. If it were only this easy, the problem would not exist today.

Knowledge by Job Function

Design Engineers must not only be knowledgeable of the fundamental principles of geometric dimensioning and tolerancing, but also be proficient in advanced applications and analysis. These advanced capabilities are needed in order to apply the proper and optimum symbology to the design parameter and also to apply the correct (as well as optimum) tolerance that clearly reflects design function.

Manufacturing Engineers also need the fundamental knowledge to understand clearly what the designer is trying to say by the engineering drawing. To be efficient, they also must have a high level of competency in applications and analysis to establish process controls that will ensure conformance to engineering requirements, but do it at the least amount of cost. One must keep in mind, the engineering drawing should not state how to manufacture or to inspect the product, but should only state, in a clear engineering language, what it should look like when it is complete.

Metrology Engineers, like the Manufacturing Engineers, need the same broad base of knowledge, except in this case, the Metrology Engineers need to have a clear understanding of how to approach the dimensional metrology aspects. This is necessary to ensure the product produced in fact conforms to the defined requirements, or more to fact, must understand the true magnitude of product and feature variation.

The little time devoted to teaching geometric dimensioning and tolerancing in educational institutions makes all disciplines in the mechanical arena today have a higher negative impact to the financial loss within companies than is necessary. It is also the single most needed focus area for all disciplines for reaching significant gains in today's sub-micrometer mechanical industries.


Each organization needs a plan to implement sound product design, drafting, manufacturing and dimensional metrology practices to ensure optimum designs are defined clearly and consistently on the engineering drawing. These organizations also must have the measurement capabilities to ensure conformance to the engineering requirements. This paper states, without hesitation, that compliance to GD&T (per the ASME Y14.5M-1994 Standard) does not mean dimensions and tolerances cannot be linear. It simply means they need to be clear and not ambiguous.

Based on the extremely tight tolerances inherent in many drawings that exist today, without the use of geometric symbology, the utilization of feature and datum modifiers, and a very clear interpretation by everyone involved, industry has very little hope of receiving a significant return on the investment made to date or that which is needed for future progress and Return on Investment. This success includes the ability to establish measures that will ensure conformance to the engineering requirements defined on the engineering drawing.

Drawings have improved greatly in regard to reflecting design intent, and they continue to improve based on standardization efforts that continue to be a focus item for many design groups, as well as increased understanding of the Y14.5 Standard. The magnitude of standardization activity will have a tremendous impact on reducing design costs, as well as manufacturing, inspection, and overall procurement-related costs.

High Costs Associated to Inadequate Drawings

The cost associated to inadequate drawings is high in terms of time lost in product ramp-up and vendor ramp-up, in-house re-engineering time, material rework, vendor surveillance, production downtime, wasted raw material and purchasing red tape. The following example/case compares the typical procurement cycle resulting from a flawed drawing with one expected from a well-researched GD&T drawing.

Case Scenario: A part is designed by G&K Industries (G&K) and will be machined by their vendor, DLS Machine Tool (DLS) (both are fictitious company names). Assume the following costs:

  G&K engineering time $80/hour
  G&K purchasing time $50/hour
  DLS billing rate $70/hour
  Raw material cost $100/part

Case 1: To start with, G&K Engineer A, untrained in GD&T, takes a week to produce an engineering drawing for a critical housing. The process consumes 20 hours at a burdened cost of $1,600 and results in a flawed drawing. In a separate effort, G&K Engineer B, trained in GD&T, takes two weeks to produce an adequate drawing for an almost identical part in 37 hours, which includes a thorough tolerance analysis plus conferences and final checks with manufacturing and quality engineering. The total burdened cost is $3,400.

The job is to let DLS produce a first run of five parts using the inadequate drawing, resulting in a charge of $2,300. The work is accomplished in one week, and G&K spends $300 inspecting the lot only to find it discrepant and unfit for rework. As a result, a meeting is called with DLS to discuss and to resolve the problem, which G&K finally admits was due to flaws in the drawing. The combined cost of the meeting and of making the required changes to the drawing is $1,820, and an order for an additional five parts is placed with DLS. The meeting and the decision process consumed one week. As a result of the drawing changes, the NC program and work holding fixture had to be changed, leading to a total cost of $2,090 for the second run of five parts, which consumed one week.

Providing grounds for high hopes, the second group of five parts passes G&K inspection at a cost of $300 and is released to pre-production, where they are discovered to be borderline nonfunctional as a result of additional drawing shortcomings. Fortunately, the parts can be reworked by DLS at a cost of $980, but at an additional in-house expense for meetings, engineering time and production delays totaling $4,260. The additional work consumes three weeks, and as a result of these experiences and efforts, the inadequacies of the original drawing are completely remedied. In review, the cost to produce the first five usable parts, starting with the flawed drawing, was $13,650 (the ramp-up time was seven weeks).

Case 2: The experiences are much different with the part designed by G&K Engineer B. The unflawed drawing permits DLS to produce the first run of five parts to specification in just one week at a total cost to G&K of $6,040!

The ramp-up time was only three weeks. As illustrated in the following table, there is a substantial cost difference between investing the time and energy to create a thoroughly researched and geometrically correct drawing, versus relying on a cycle of experimental machining, MRBs (material review board) and ECOs (engineering change orders) to achieve the same goal. Failing to put forth the effort at the beginning more than doubled the cost and ramp-up time:

Cost Comparison Summary

Cost Related to Drawings

G&K Engineer A
Ambiguous Drawings
G&K Engineer B
Non-Ambiguous Drawings

Initial engineering cost



First run mfg. cost



First run inspection cost



First re-engineering cost



Second run mfg. cost



Second run inspection cost



Second run rework charges



Second run extraordinary in-house cost



Second run re-engineering cost



Total cost investment to produce




Drawing time

1 Week

2 Weeks

Mfg. (ECO) time

6 Weeks

1 Week

Total required time frame to produce

7 Weeks*

3 Weeks*

*Cost and time overrun is $7610 and 4 weeks

The above example reflects greater than a 50% decrease in overall cost and lead time due to utilizing an engineering language that clearly reflected the design intent and could easily be understood.

The following are a few of the key areas that recognized cost savings and reduced overall cost in this analysis:

  Less engineering time
  Less material rework
  Reduced product deviations
  Fewer meetings
  Less supplier time (confidence/communication)
  Fewer CRs/ADRs/DMRs
  Less inspection time
  Reduced lead time
  Reduced tool maintenance

Five-Year Projection

Based on a survey of 20 technical buyers and procurement engineers within one organization, the above example is reflective of roughly 50% of the designs and builds for tooling. The remaining 50% varies to a lesser degree depending on the supplier and the length of time they have been doing business together. Current dollars spent by this organization for tooling alone was in the range of $10 million, with projections for increase to be greater than 20% each year. Note: tooling dollars reflect roughly 3.5% of gross sales for this organization. Based on the above noted percentages, the following matrix outlines approximated potential savings over a five-year period:

Five-Year Projection


Dollars (in Millions)
Spent on Tooling
Projected Savings Based on 50%















Total for 5 years



Over a five-year period, if no changes were made to the technical competencies and proficiencies of the organization, roughly $37.3 million would be unnecessarily spent. If this organization recognized only 25% of the projected savings (which was 50% of the total dollars spent), they still would recognize a savings of $9.3 million. Most would agree this savings would be significant enough to get one's attention.

These are factual projections that did, in fact, get this company's attention and based on this, a tremendous project was initiated to integrate into the organization standardized methods for dimensioning and tolerancing.