Known as the "Doctor
of Dimensioning," Alex Krulikowski is a noted educator, author, and
expert on Geometric Dimensioning and Tolerancing (GD&T). A design
manager with one of the world's largest manufacturing corporations,
he has more than 30 years of industrial experience putting GD&T
to practical use on the shop floor.
Parts, Good Measurements
A machine tool
must be capable of generating both, says a software company with
a new vision for the role of metrology data in the emerging era
of globally integrated manufacturing enterprises. Article by
Mark Albert in Modern Machine Shop Online.
To read more about
Read about quality
technicians who must work with tolerances as small as 0.0005 millimeters
in this article from the October 2001, Quality Online E-zine.
To read more about
case you missed it: check out this GD&T article from
the 1997 Quality Online Archives
the Language of
knowledge of geometric dimensioning and tolerancing (GD&T)
is necessary to truly understand the designer’s intent and to
plan an accurate and appropriate inspection of the product the
article on GD&T by Melissa Larson in the May 1997 Quality
Online archives has quotes from Alex. Click
start-to-finish self-training course in geometric dimensioning
and tolerancing has become a classic in the field. Learn GD&T
at your own pace, using problems from real life applications.
Thirty targeted lessons give you an insider's grasp of GD&T.
To read more about
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out more about what ETI has to offer your organization.
to date on the latest industry news with the ETI Tech Calendar.Click
improvement will result from people improving their processes
and management improving the system.
Pyzdek, from Pyzdek's Guide to SPC: Applications and Special
is a regular online publication devoted to Geometric Dimensioning
& Tolerancing. Each edition features a host of GD&T resources
and links, as well as dimensioning tips by noted GD&T author and
ETI founder, Alex Krulikowski. We also invite you to visit our website,
Functional vs. Variable
When selecting inspection
methods for product evaluation, a choice must be made between
dedicated functional gaging vs. flexible variable measurement
using a CMM or open set-up. This comparison highlights differences
that exist between the two.
or Hard Gaging)
or Surface Plate Layout)
size, Rule #1, location, and/or orientation of entire
part feature. Capable of checking multiple part features
simultaneously. Provides a pass/fail answer for a part
feature tolerance specification.
Z coordinates (at probe contact points only). Checks size
independent of location. Manual or software estimates
used for Rule #1 and effects of maximum material condition.
Provides variable data for a measurement.
for functional "fitness for use" inspection. Gage
acts as worst-case mating part.
and easy to use. Minimal training required. Little
judgment required making pass/fail decision.
operators or auditors can do the inspection near
the production line, reducing moving and wait
tolerances may be biased to eliminate user's risk.
produce quick results for process control (variable
gaging) or product acceptance (functional gaging).
information or machine/process adjustment and
costly dedicated gages.
operator (human feel) sensitive.
to get data on additional features if requested.
(Not limited to features built into the gage.)
of gage and lead-time required.
flexible--changes take time and may be costly.
gaging or functional gaging provides little or
no information usable for process adjustments
or capability analysis.
gage requires periodic maintenance and/or calibration.
operator sensitive in some cases.
may become obsolete if part is changed or discontinued.
tolerances reduce manufacturing tolerances.
inspection does not assure functional product.
Translation to MMC provides only an estimate of
at probe points only--may not detect local variation,
form error, or orientation error that could destroy
"fitness for use."
high-cost equipment and highly trained personnel.
uncertainty (error) is difficult to quantify and
bias to reduce user's risk.
between inspection sources are difficult to avoid
costs for programming and operation.
take hours or days to get results.
developed programming or software may differ from
other operators or established standards.
quick verification of "fitness for use" on higher
volume or expensive parts.
verification of higher risk parts and characteristics.
applications would address hole patterns, critical
features, irregular forms, location, and orientation,
and "fit" characteristics.
parts that will be offered as individual service
components. Because parts must mate with customers'
components regardless of age, source or condition,
receiver gages are recommended.
when measurement uncertainty must be minimized.
roundness or straightness variation is present:
(form variation can cause "measured size" to differ
from "effective size" and adversely affect fit
within mating parts).
bend, twist, bow, warp, or other distortion is
present. (Fit and function are affected by maximum
material and virtual conditions; these may be
impossible to properly check with variable measurement
methods.) Plastic parts, multilevel stampings,
and subassemblies of moving parts are examples
of products that are difficult to check properly
by other means.
initial sample analysis, product/product development
and capability analysis*
low volume or short-lived products*
quick answers are needed and no gage is available.
low-risk measurements or proven capable processes
requiring infrequent sampling, where form or orientation
error is insignificant.
adjustment, debugging and troubleshooting of equipment
positional measurements at RFS.
May need separate form measurement and analysis requiring
cumbersome and/or uncertain translation of RFS data
to estimate MMC and virtual condition relationships.
Consideration of the
advantages and disadvantages suggests that each approach has its
place, and at times both might be needed. It is
important to recognize that the results obtained from one method
may not agree with the other. In any case, the functional
evaluation must govern the acceptance of the product.
welcome your feedback. Send comments about this article
opinions will be posted in the next issue.
Standards in the News takes a look at real-life issues where standards
have failed or need improvement. This month: lack of standards hinders
e-business supply chain automation.
Excerpts from Computerworld
LACK OF STANDARDS
BLOCKS SUPPLY CHAIN AUTOMATION
New Orleans -- A lack
of standards has become a huge barrier to using e-business technology
to automate corporate supply chains, and there currently is no
real solution in sight.
A number of corporate
users expressed doubts that any initiatives will produce standards
that meet with widespread acceptance. And until that happens,
they said, companies trying to automate their supply chains will
have to continue relying on a jumble of different technologies
and communications channels. The current lack of business-to-business
standards is the single greatest barrier to implementing Web-based
supply-chain systems for many large users, according to Scott
Stephens, chief technology office at Pittsburg-based Supply Chain
Creation of common e-business
definitions and data formatting techniques were touted as being
of "paramount" importance. "It's a huge problem in some industries,"
Stephens said. Full
from the article, "Lack of Standards Blocks Supply
Chain Automation" by Marc L. Songini in Computerworld,
April 5, 2001.
The ETI Mailbag
a question about bonus tolerance. Could you let me know the table
of bonus tolerance in the case of LMC just like in the case of
MMC in the Fundamentals of Geometric Dimensioning and Tolerancing
textbook? Whenever I teach the course to my students, they ask
me similar questions; however, I cannot make that table. Please
the LMC modifier is used in the tolerance portion of a feature
control frame, a bonus tolerance is permissible. In the case of
LMC, bonus tolerance works just the opposite of bonus tolerance
with MMC. The chart compares bonus tolerance with MMC to bonus
tolerance with LMC.
on page 257 in the Fundamentals of GD&T, 2nd Edition,
textbook, Figure 9-7 shows a chart with bonus tolerance at LMC.
If you have any further questions, please let me know.
teaching ideas to new products that will assist you in training or
on the job, the ETImail Tech Tip will keep you informed about new
technology and ideas. This month's Tech Tip tells which dimensioning
habits to avoid.
THE TEN WORST DIMENSIONING
- Dimensioning the
part without understanding how it functions in the system
- Using coordinate
dimensioning instead of GD&T
- Using RFS when
MMC or LMC would work
- Arbitrarily using
the outside or convenient surfaces of the part as datum features
- Copying tolerances
from similar production parts
- Labeling centerlines
- Use of restrictive
general or titleblock tolerances without using more generous
tolerances where possible
- Requiring the
drawing user to make assumptions
- Applying GD&T
and datums last to the part
- Not controlling
all features on a part (for size, location, orientation, and
you know about a new tech tool or an innovative idea
that would aid
readers, please write us: ETImailbag.
comments about anything you've read in ETImail? ETI will
post your comments here and provide a forum for more discussion
about GD&T topics.
about ETImail Archives:
find the ETI Newsletter very informative and was wondering if
there is a way to access the prior issues. Thanks, Erroll W. Green
to hear you are enjoying ETImail. Since we now have 3 back issues,
our website administrator has created an archives section on the
home page of our website, etinews.com.
To access previous issues of ETImail, simply click on the link
in the left menu column, under ETI, then ETInews. There you will
find the current issue, the archives, and an option to subscribe
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