TOLERANCE DESIGN : EXPRESSING DESIGN INTENT
IN DRAWINGS
Shigeo HIRANO1, 2 Susumu KISE2, Sozo SEKIGUCHI 2 , Kazuya OKUSAKA2
and Tsutomu ARAKI3
1
Professor emeritus, Tokyo City University, Japan
2
Artner Co. Ltd, Japan
3
Professor emeritus, Tsukuba University of Technology, Japan
ABSTRACT: Despite the improvement in the performance of machine tools, the dimensions andshape may vary from part to part even if all parts have been processed in a similar manner. Efforts
are made to minimize this discrepancy (variation or nonuniformity) in both design andmanufacturing stages, however, it is impossible to completely eliminate the discrepancy. Basically,
the dimension of parts varies above or below its target value. The allowable range of discrepancy
should be determined considering all related factors, including the specifications and manufacturing
cost of a product. Recently, we have often heard those involved in manufacturing say that all parts
have been processed according to the instructions of designers but that those parts cannot be
assembled or do not work after assembly. In many cases, this is because designers do not correctly
understand what tolerance design is and they do not implement it in a proper manner. Also, forvarious reasons, designers do not have much access to the information about the requirements
arising from manufacturing processes. These factors result in a negative spiral of an increased costof failure and delay in the development of the next version of products. When designers specify atolerance, they express their intent in drawings, comprehensively considering both the functions andperformance expected of a product and the manufacturing cost. In this study, I will show thattolerance design, namely, the skill of being able to express the design intent in drawings, andgeometrical tolerance, namely, the skill of being able to convey the intent correctly, work together
as two wheels of a cart. Also, the skill of geometrical tolerance alone is not enough to create
drawings that meet global standards. Geometrical tolerance should be based on correct tolerance
design. A real example demonstrating this point is provided and discussed in this paper.
Keywords: Tolerance design, Global standard drawing, Geometrical tolerance.

1. INTRODUCTION
Vehicle recalls and market complaints about
electric appliances are a source of concern forJapanese companies. They are attributed inpart to “variation”, which will be reduced byproper tolerance design.
Noteworthy activities that are taking place inJapanese companies regarding tolerance
design are the introduction of geometricdimensioning and tolerancing (GD&T). As
a result of the revision of the JapaneseIndustrial Standards (JIS) in March 2016,
applying GD&T to all drawings became

indispensable. My concern is that somepeople desire only the application of GD&T
to drawings, although few may have such abiased view.
It is true that GD&T isessential. However, what most business
managers really want is not merely to replace
conventional drawings with the ones
incorporating GD&T but a design revolutionthat will bring about an improved quality ofdrawings in which, for example, designers
and engineers learn both tolerance design and
GD&T.
In this study, I will show that tolerance design,namely, the skill of being able to express thedesign intent in drawings, and geometricaltolerance, namely, the skill of being able toconvey the intent correctly, work together as
two wheels of a cart. Also, the skill ofgeometrical tolerance alone is not enough tocreate drawings that meet global standards.
Geometrical tolerance should be based oncorrect tolerance design. A real example
demonstrating this point is provided anddiscussed in this paper.
2. TOLERANCE DESIGN
It is generally considered that discrepancy inthe dimensions of parts is unavoidable andthat it is acceptable if the final discrepancy is
within the range of tolerance specified on
drawings.
This is how manufacturers
understand tolerance. On the other hand, fordesigners, tolerance is something they must
set with a sense of responsibility on the basisof a balanced view of product specifications,manufacturing conditions, and manufacturing
cost.
They should determine, from acomprehensive perspective, whether a productprocessed with the specified tolerance willmeet the specifications of the final productand if the product can actually be processedwith the specified tolerance.
In the actual design process, tolerances are
determined as shown in Figure 1. In orderfor the specifications of finished products to
be within a certain range of values, those ofeach unit must be within a certain range ofvalues. Tolerances are allocated to each partin accordance with this range of values. Thisis the proper design process (1) where
designers’ intent is reflected.
In terms of finished products, more strict
tolerances are desirable for making products
smaller and thinner. In terms of ease (a cost
reduction) of manufacturing parts, however,more relaxed tolerances are desirable. Thisis the requirement arising from (2)manufacturing processes.
Naturally, cost
increases when more strict tolerances are
specified for individual parts. On the other

hand, the risk of failure in finished products
increases when more relaxed tolerances are
specified, which may result in an increase intotal cost in some cases.
(1) Designers’ intent
The strictest tolerances possible are
Desirable in terms of the quality offinished products.
Specifications ofFinished products(dimensions)
Panel block

Liquid crystal
panel
Panel fixedframe
Panel suppression

Folding
Cellular phone

Battery block

Giving up board
Panel cushion

Circuit block(2) Requirements arising frommanufacturing processes
More relaxed tolerances are desirable
in terms of ease (a cost reduction) of
manufacturing.
Figure 1: Determination of tolerances.
Tolerance is determined by balancing these
two factors, the (1) designers’ intent and the(2) requirements arising from manufacturing
processes, which are projected onto acommon axis, that is, economic efficiency(cost).
The process of calculating andspecifying tolerances while taking into
account statistical information is called
tolerance design.
Recently, designers do not often have muchaccess to the information about the (2)requirements arising from manufacturing
processes for various reasons such as the shiftof production overseas. Under suchcircumstances, a system that facilitates asmooth exchange of (1) and (2) must be
constructed in order to implement proper
tolerance design.
2.1 Tolerance design and GD&T work
together as two wheels of a cart
As mentioned above, tolerance design and
GD&T work together as two wheels of a cart.
When considered as two wheels of a cart, they
can generate synergistic effects that bringabout a better quality of drawings. As aresult of the revision of JIS, the introductionof GD&T has become essential. The qualityof drawings will be dramatically improved if
GD&T is combined with tolerance design.
Most designers aim to achieve the following
four goals in tolerance design.
1) Realization of product functions
2) Stabilization of product quality
3) Determination of part tolerances
4) Clarification of management priority points(points to be used as references, points to becontrolled, and intended level of control)
Without achieving these goals, the quality ofdrawings will not be improved and neither candesign revolution be realized. Tolerance
design plays a crucial role in theaccomplishment of design revolution.
The following is the mechanism of synergistic
effects generated by the combination oftolerance design and GD&T. In a sense,
GD&T is a common area whereas tolerance
design is a competitive area. All designers
must learn GD&T because it was adopted byJIS.
However, there will be little
differentiation in drawings if all designers
master GD&T.
What really affects thecompetitiveness of drawings is tolerance
design because, in general, the know-how oftolerance design is accumulated and cultivatedwithin an individual company. It is naturalthat the know-how of tolerance design, inother words, a source of competitiveness, israrely provided to outsiders.
The proper tolerance design is therefore
essential to enhance the competitiveness ofdrawings. Synergistic effects are generated

by the combination of tolerance design and
GD&T because the motivation of designers tolearn GD&T will markedly increase as theylearn tolerance design. Also, as designers
learn tolerance design, they will become moreaware of the necessity and significance of
GD&T.
Namely, in tolerance design, designers
identify the points in drawings that are to be
used as references or to be elaborated. By
repeating these steps, they can reduce waste,focus on necessary tolerances, and thenspecify those tolerances using GD&T. In
time, a significant change will be seen in thedrawings.
The number of specified
tolerances will markedly decrease and thenumber of items to be controlled inprocessing and measurement will also greatly
decrease, resulting in a cost reduction and an
improved quality of products.
2.2 Actual situation of tolerance design inJapanese companies
When asked, most managers in design
departments will say that they are carrying out
proper tolerance design. However, in fact,many Japanese companies do not or only
partially carry out proper tolerance design.
Very few designers and engineers have a fullunderstanding of tolerance design and put it
into practice. One of the reasons for this isthat tolerance design is a competitive area, as
described above.
There are few opportunities to learn tolerance
design because it is a competitive area andaccumulated know-how for a company.
Designers rarely see how tolerance design iscarried out in other companies, so the only
opportunity to learn tolerance design ison-the-job training (OJT).
However,recently, OJT is not working well in many
companies.
Conventionally, designers used to carry out
tolerance design, create drawings, and thenbring them to production sites to ensure thatthe tolerance design is appropriate throughdiscussion with engineers who are responsiblefor processing or measurement.
Designdepartments stock many books on tolerance
design that designers can refer to. They canalso ask for the advice of more experienced
designers when they are working on some key
points in tolerance design.
Now, designers are incomparably busier than
before. Experienced designers are so busy
that they do not have time to teach young
designers. In addition, OJT is not working
as well as it used to be because
three-dimensional (3D) CAD is used andpreviously created drawings are easily utilized
or copied. The lack of understanding of
tolerance design in design departments has
not become such a big issue because it has
been compensated by production departments.
Now, however, there are fewer skilled
engineers in production departments anddesigners cannot continue to depend on
production departments.
For designers, tolerances are a very basic
aspect of design. An increasing number ofcompanies now encourage their employees tolearn about tolerances all over again. The
following is the current situation at
manufacturing sites.
An alarming situation was revealed when
young and skilled designers had gathered to
discuss tolerance design. Young designers
indeed really lack knowledge about tolerance,but skilled designers are not aware of this fact.
Young designers often utilize the tolerances
specified for similar parts that were
manufactured in the past, even when they
design completely new products (parts).
Tolerance design may be a very basic skill forskilled designers but young designers lackknowledge about it.
2.3 Global manufacturing
The change in production sites is anotherreason why the issue of tolerance has recently
become obvious. Under the circumstancesof the know-how of tolerance design not
being passed on to young designers and oftolerances not being properly specified, thekey to maintaining the high-quality
manufacturing in Japan was the excellent
technological responsiveness at production
sites.
However, such technologicalresponsiveness at production sites is no longer
expected with production being shifted
overseas. Any deficiency in design drawings
leads directly to trouble. When the products(parts) are processed as directed in design
drawings, that is, nothing more or nothing lessthan the values specified in the drawings, but
do not work, the failure will result in extra
cost to design departments. In fact, most of
the trouble occurring at production sites
overseas is a result of processing products justas directed in design drawings.
In order to promote global manufacturing andto manufacture high-quality products at low
cost, there is an urgent need for Japanesecompanies to encourage their employees tolearn about tolerances, the basic of drawings,
all over again and to review the quality ofdrawings.
2.4 Merits of learning tolerance design
1) Acquiring ability to develop an
appropriate design on the basis of thetheory of tolerance calculation andcriteria for judgment
In the study of the designers who say they do
calculate tolerances, most of them answeredthat experienced designers taught them how to
calculate tolerances (OJT) or that they learned
it themselves. Many designers are often
unsure about tolerance calculation and quite afew designers calculate tolerances improperly.
If designers learn the theory of tolerance
design systematically, they will become able
to calculate tolerances with more confidence
and to instruct younger designers proper
tolerance calculation. The most difficult
aspects in tolerance design are making
judgments and taking appropriate measures.
It is important to calculate basic tolerances,
process capability indexes (Cp and Cpk), andpercent defective properly and then to makejudgements and take appropriate measures onthe basis of the obtained values.
2) Acquiring ability to prevent design
quality problems in a theoretical method
before they arise
Once a product is designed, there is no need
to wait for identifying issues until the productis actually manufactured; all details of the
product are determined by the design.
Referring to design drawings, engineers caneasily know the kinds of defects (troubles andfailures) that will occur and the probability ofsuch defects (percent defective) if all parts areprocessed and assembled as directed in thedrawings. This is called failure mode andeffects analysis (FMEA). In tolerance design,designers calculate the probability of defects
in each item and try to reduce that probability.
3) Acquiring ability to properly evaluate thedesigns of other designers
Leaders in design departments need topromptly evaluate the appropriateness ofdesign drawings created by the designers
working under them and give necessary
advice (check of drawings). They should
pay attention to some important design points
and calculate the tolerances (manual
calculation) of those points. If there seem tobe any errors, it is necessary to review thetolerance calculation sheet created by thedesigners in charge. If there are any errors,
the leaders should tell the designers what iswrong and how to fix it to make the design
appropriate.
For the leaders in design
departments, these steps are crucial not onlyin checking drawings but also in coaching anddeveloping young designers.
3. EXAMPLE OF TOLERANCE DESIGNIn this section, an example of the tolerance
design of single-component products leading
to cost reduction and the prevention ofimitation is described.
When explaining the necessity of tolerance
design, I am often asked about thesignificance of tolerance design for
single-component products.
Some maythink that, if a product is to be manufactured

only once, it is not necessary to specify a strict
tolerance for each part in the design process
because, even if the dimensions of parts aredifferent from those specified in drawings, theparts can be modified or adjusted duringassembly.
This is, however, a big
misunderstanding.
1) Demerits of modifications and adjustments.
Here, the demerits of modifications of parts or
adjustments during assembly are described.
Aside from the loss of time and cost spent inmodifications and adjustments, the final
quality of products is affected by the skills
and sense of engineers because a flexible
responsiveness is required in those processes.
Although inspections are carried out after
assembly to ensure the quality of products,
there will be underlying differences in quality,
which do not appear in drawings or
specifications.
Also, it is common to manufacture a variety
of products that are similar to asingle-component product.
Parts withexactly the same drawings or partly modified
ones may be used for manufacturing similar
products.
If the information about themodifications and adjustments made in the
manufacturing of a single-component productis not recorded on drawings but only stored in
the memory of the persons who were in
charge,someotherwise
unnecessary
modifications and adjustments must be
repeated in the manufacturing of a similar
single-component product. This issue may
be partly solved by keeping a record of themodifications and adjustments, but this ishardly a fundamental solution because
difficulties still exist in specifying anddetermining the range of their applications.
Moreover, the dependence on adjustments
during assembly can lead to easy productimitation. If a product is designed on thepremise that it will be adjusted duringassembly, namely, if the performance orfunctions of the product are realized throughsome adjusting mechanisms prepared in thedesign process, such a product can be easily

imitated by reverse engineering.
The
product can be imitated by copying the roughshape and dimensions of parts and thenadjusting those parts to achieve the intended
performance.
All the above issues can be solved by proper
tolerance design in the design process. In
other words, the role of tolerance design is tosolve those issues.
The reduction of
man-hours spent on modifications andadjustments will lead to cost reduction.
Unless drawings are leaked, the tolerances
specified for each part will not be revealed,even by reverse engineering. The know-how
to realize the performance and functions of
the product is guarded.
2) Variation exists even in single-component
product.
Tolerance design is the process of design
taking into consideration variations ofdimensions. For many people, the word“variation” brings up an image of a lot ofparts of the same kind.
The actual
dimensions of a part are distributed centering
around the dimensions specified in a drawing.
Some may therefore think that variation does
not exist in single-component products
because they are manufactured only once.
However, variation does exist, even insingle-component products.
There arevarying degrees of differences between thedimensions of processed parts and thosespecified in drawings.
Variation is thedegree and probability of such differences.
In tolerance design, variation and its effects
are estimated to determine the shape anddimensions of parts and, in some cases, tospecify the allowable range of variation as atolerance.
Similarly to the variation in mass products,
the variation in single-component products
can be estimated on the basis of processcapability. Designers allocate tolerances foreach part utilizing its full range of processcapability. Unnecessarily strict tolerances ortolerances that always require modifications
after processing or adjustments duringassembly lead to cost increases. Designers
should understand the accurate processcapability of individual parts that make up the
product they design. For this purpose, it isimportant to examine the information about
the products manufactured in the past and to
go to the production sites to obtain more
information. Of course, it is necessary toreview the process capability when any
changes are made in the method of processing,the materials, and the manufacturers. Thesechanges are generally called 4M (man,machine, material, and method) changes.
How these changes are controlled is also
important.
4. OVERVIEW OF GD&T AND
MAXIMUM MATERIALREQUIREMENT
4.1 From dimensional tolerances to GD&T
In global manufacturing, the final quality ofparts must be ensured regardless of thecountry where the parts are processed, theexperience of the persons processing the parts,and the machines used in processing. To
realize this, the basic premise is to eliminate
ambiguity in the specification of tolerances indrawings. The elimination of ambiguity willlead to the prevention of not only any
unexpected decrease in the precision of
products but also a cost increase due to an
unnecessarily high precision of products.
The greatest reason of ambiguity remaining in
drawings is that most tolerances are defined as
dimensional tolerances. Figure 2 shows arectangular front view and a rectangular sideview for which the height, width, and depth
are specified in the drawing. The engineer
who creates this drawing expects a cuboid but
the manufactured part rarely has a cuboid.
When dimensional tolerances are used, there
remains the possibility that the processedshape will become irregular because theaccuracy of a shape is basically checked bymeasuring the distance between two points.
The ambiguity can almost be eliminated if theflatness of a plane and the parallelism andsquareness with respect to a reference plane
are defined by GD&T.
15±0.110±0.110±0.1

Designer's image

Where are thebase level andthe reference line
Datum

A correct plane

Is itright-angled
correctly

Figure 2: Ambiguity remaining inDrawings
Using dimensional tolerances, only astraight-line distance between two points is
controlled, in principle. For example, when
the tolerance of height is specified as 10±0.1
mm, the height must be within the range from
9.9 to 10.1 mm at any point. A shape canmeet this dimensional tolerance requirement
even if the top and bottom surfaces are
considerably curved in the same direction
while remaining parallel to each other or theside view of the shape is distorted like aparallelogram. Again, accurate manufacturingon the basis of dimensional tolerances has
been possible because the persons working at
production sites in Japan have sophisticatedabilities to manufacture products with nobends or distortions even when it is not
specifically directed.
To avoid irregular shapes such as thosementioned above, it is necessary to clearly
define the flatness of a plane and theparallelism and squareness between twoplanes using GD&T. The shape, position,and location of points, lines, and planes
including the flatness, which defines theevenness of a plane surface, and thesquareness, which defines the vertical angle ofa plane with respect to a reference plane, canbe controlled using GD&T.
GD&T itself is not a new technique but has
not been common in Japan because it had notbeen much needed, as explained above.
Another barrier to the widespread use of thistechnique is that, compared with dimensional
tolerances, many engineers find it moredifficult to understand the concept of GD&T
or how to give directions using this technique.
In the future, however, GD&T will become
essential in the manufacturing industry inJapan, because designers should communicate
their intent accurately and promptly in orderto keep up with globalization and to meet thedemands for quality improvement.
4.2 Overview of maximum material
requirement
A circled M indicates the application of the
maximum material requirement. By thismethod, GD&T values can be relaxed inconjunction with dimensional tolerances sothat the number of conforming products canbe increased (Figure 3).
There is a shaft of 10 mm in diameter. The
dimensional tolerance for the diameter is
specified as ±0.1 mm, and the straightness is
specified as φ0.2 mm. In general, thestraightness φ0.2 mm applies to every
diameter of the shaft regardless of its
dimension. With the application of the
maximum material requirement, however, thestraightness can be interpreted to be φ0.4mm if the diameter of the shaft is 9.9 mm

because it still meets the purpose of inserting
the shaft into a hole of a certain diameter.
φ10±0.1

φ10.1

φ0.2

M

φ10.1

φ10.1

straightness
φ0.2
(a)
φ9.9

φ9.9

φ9.9

straightness
φ0.4(b)Figure 3: Example of maximum material
requirement
Compared with dimensional tolerances,
GD&T often requires higher precision inprocessing because it eliminates ambiguity.
With the skillful use of GD&T, however, theparts that were conventionally identified as
nonconforming products can be used asconforming products.
Dimensional tolerances and GD&T arebasically independent of each other, but they
are considered in conjunction with each otherwhen maximum material requirement isapplied.
In short, maximum material
requirement allows the relaxation of GD&T

values in accordance with dimension values.
In the above example, the dimensional
tolerance is specified as φ10±0.1 mm and thestraightness is specified as φ0.2 mm in thedrawing. Therefore, the external diameter ofthe shaft is 9.9–10.1 mm and the central axisof the shaft is within 0.2 mm in diameter.
Here, we consider the purpose of specifying
the tolerance for the shaft. For example, if
the tolerance is required to insert the shaft intoa hole, the primary purpose of specifying thetolerance is to be able to insert the shaft into
the intended hole.
The following logic is true in this case. In
order for all shafts processed as describedabove to be inserted into a hole, the hole musthave a diameter of 10.3 mm or more [Figure 3(a)] so that the shaft 10.1 mm in diameter witha bending central axis can be inserted intosuch a hole.
With a diameter of 9.9 mm, a shaft with astraightness of φ0.4 mm or 0.2 mm can beinserted into such a hole [Figure 3 (b)].
Namely, if the purpose of specifying thetolerance is to insert the shaft into theintended hole, no trouble will arise if therequirement for straightness is relaxed inaccordance with the shaft diameter.
As shown by this example, the maximum
material requirement is used mainly toprevent
interference
betweenparts.
Alternatively, GD&T can also be relaxed byusing the lowest material requirement, which
is often used for ensuring minimum thickness.
By flexibly using these two methods in
combination with GD&T, the number ofnonconforming products can be decreased,leading to cost reduction.
5. CONCLUSION
Tolerance design and GD&T are essential inresolving the issues of variation in
manufacturing, cost reduction, and preventionof trouble and failures such as malfunction
and improper assembly of products
manufactured overseas.

When designers have a correct understandingof tolerance and carry out tolerance designfrom the early stage of design, they canprovide a well-balanced design, taking
account of both quality and cost. Also,
GD&T is essential for the correct expressionof the design intent to later processes.
However, the use of GD&T and education on
it are lagging behind in Japan.
Ambiguity and differences in interpretations
are removed from drawings when directions
are appropriately provided using geometrical
product specifications (GPS), which was
discussed in the ISO/TC213, and GD&T,
which is a universal design language. With
such drawings, it is possible to prevent trouble
such as a difference between the design intent
and the finished product that commonlyoccurs, particularly when production sites arelocated overseas.
In addition, because of the revision of JIS in
2016, it became necessary to define therelative position of objects using notconventional dimensional tolerances but
GD&T. Proper tolerance design and theapplication of GD&T are both essential for
improving the quality and competitiveness ofdrawings.
REFERENCES[1] ISO/DIS 1101: 1996 [Geometrical productspecifications (GPS)−Geometrical tolerancing−Tolerancing ofform, orientation, location and run-out.
[2] ISO17450-1:2011Geometrical productspecifications (GPS)−General
concepts−Part 1: Model for geometrical
specification and verification.
[3] ISO 17450-2:2012 Geometrical productspecifications (GPS) −General
concepts−Part 2: Basic tenets,
specifications, operators, uncertainties andambiguities.
[4] JIS B 0401-1: 2016 Geometrical productspecifications (GPS)-ISO code system fortolerances on linear sizes-Part 1: Basis oftolerances, deviations and fits.

[5] JIS B 0420-1: 2016 Geometrical productspecifications (GPS) -Dimensional
tolerancing-Part 1: Linear sizes.
ABOUT THE AUTHORS
1. Shigeo HIRANO Ph.D. Professor
emeritus Tokyo City University, Tokyo,
Japan. His research interests areTechnology Philosophy, Engineering
Ethics, Mechanical Design and Drawing,
CAD Design System Education andDevelopment of New Products for
Human Support Science.
He can be reached by e-mail:rs4775hirano@ybb.ne.jp, Professor
emeritus, Tokyo City University
1-28-1 Tamazutsumi, Setagaya-ku,
Tokyo, Japan, 158-8557
2. Susumu KISE, is the Ability
Development Section Supervisor in the
Artner Co. Ltd. e-mail:kise@artner.co.jp,
Artner Co. Ltd Sumitomo Nakanoshima
Building 2F, Nakanoshima 3-2-18, Kita
Ward, Osaka City, Japan, 530-0005
3. Sozo SEKIGUCHI, is the President in the
Artner Co. Ltd.
e-mail: sekiguchi@artner.co.jp
Artner Co. Ltd Sumitomo Nakanoshima
Building 2F, Nakanoshima 3-2-18, Kita
Ward, Osaka City, Japan, 530-0005
4. Kazuya OKUSAKA, is the Ability
Development Section General Manager
in the Artner Co. Ltd.
e-mail:okusaka@artner.co.jp
Artner Co. Ltd Sumitomo Nakanoshima
Building 2F, Nakanoshima 3-2-18, Kita
Ward, Osaka City, Japan, 530-0005
5. Tsutomu ARAKI, Professor emeritus
Tsukuba University of Technology,
Tsukuba, Japan. His research interest is
education of Computer Aided Design,especially for hearing-impaired students.
He can be reached by e-mail:tutaraki@yahoo.co.jp,Professor emeritus,
Tsukuba University of Technology
4-3-15 Amakubo, Tsukuba City, Japan,
305-0005