Turning Ideas

Into Reality

An Overview OfAn Overview Of

GPSA Cost Saving ToolA Cost Saving Tool

First Edition

2005

Geometrical

Product

Specifications

Per Bennich

and

Henrik Nielsen

© IfGPS 2005 1

GPS - Geometrical Product Specificationsand the GPS-matrix system

SynopsisGPS is the international symbol language for expressing tolerances in technical drawings. It is the only worldwidelanguage available for communicating geometrical requirements on drawings. GPS is developed throughcooperation by more than 60 countries and documented in ISO Standards issued by the InternationalOrganization for Standardization. GPS is a natural development of traditional tolerancing, or GeometricalDimensioning and Tolerancing, GD&T as it is known in the US. What has been added is much more detaileddefinitions of the requirements. This allows designers to express functional requirements much more preciselythan was previously possible. The potential benefit is a 15% reduction in manufacturing cost, and the paybacktime for the investment in training and updated documentation can be less than 2 years.

To realize these savings it is necessary to educate not only designers, but all personnel that use GPS toexpress and interpret geometrical requirements. It is also necessary to educate designers in the properprocedure and sequence for applying tolerances on drawings, so the tolerancing is unambiguous and trulyexpresses the functional requirements.

These skills are not taught at engineering schools or in basic tolerancing classes. Consequently, the vastmajority of drawings used in industry today are ambiguous and do not communicate the true functionalrequirements of the parts. These drawings impose artificial constraints on manufacturing and in some casesallow non-functional parts to be accepted and passed on to assembly. The savings from implementing GPScomes from eliminating these types of waste.

While all companies involved in designing and manufacturing mechanical parts can benefit from implementingGPS, the advantages are greatest for those companies that subcontract or outsource the manufacturing ofparts because these companies, more than any others, have a need for their drawings to be able to communicatefunctional requirements without further explanations.

What is GPS?GPS in this context is the acronym for GeometricalProduct Specifications. GPS is the modern andupdated symbol language that is used fortolerancing and communicating requirements topart geometry in technical drawings. GPS is thecommon international tolerancing language andis used worldwide. The basis for GPS tolerancingis geometrical dimensioning and tolerancing(GD&T), but used in a new and different way.

Why this GPS document?GPS is new and most companies are unaware ofthe significant savings and competitiveadvantages GPS can bring. The purpose of thispamphlet is to explain GPS in layman’s terms and

The basis for GPS tolerancing istraditional geometrical

tolerancing, but used in a newand different way.

point out where the potential savings are, as wellas outlining how you go about implementing GPSas the tolerancing language in your company.

The GPS advantageYou can gain technical, competitive, andeconomic advantages by implementing GPS asthe tolerancing language in your drawings. Somecompanies report a payback of the investment inless than 2 years, primarily due to a reduction inmanufacturing cost and a reduction in workstoppage due to non-functional parts jammingassembly lines or lack of functional parts idlingproduction.

GPS is first and foremost about better, moredetailed and precise communication amongstdesign, manufacturing, and metrology personnel.The savings come from fewer misunderstandingsand getting it right the first time. A term that is keyto understanding the advantage of GPS isspecification uncertainty. It quantifies theambiguity in a tolerance requirement when it isapplied to a real part with form error and angular

© IfGPS 2005 2

deviations. See figure 1. As tolerances havebecome tighter in recent years, the specificationuncertainty in traditional tolerancing has becomemore significant. This is the motivation for thedevelopment of GPS.

A term that is key to understandingthe advantage of GPS isspecification uncertainty.

Figure 1: a) Nominal (perfect) part.b) Real part with form errors and angular

deviations.What are the signs that indicate mycompany would benefit from GPS?

There are a number of clear signs that a companywould benefit from implementing GPS tolerancing.However, these signs are often misinterpreted,so companies think they have other problems,when in reality it is their product documentationand their tolerancing on the drawing that areinsufficient.

These signs include:

- Your supplier delivers some parts that hehas measured to be good, but when youmeasure them, you find them out oftolerance.

- You often use engineering deviations touse parts that are out of tolerance, butyou know will work anyway.

- You use a purchased parts approvalprocess (PPAP) to lock down themanufacturing processes used bysuppliers instead of relying on thetolerances in your drawings to define theacceptability of parts.

All of these symptoms indicate that the tolerancingin your drawings does not correctly express thefunctional requirements of the part.

Are you subcontracting or outsourcing?GPS based drawings provide an advantage whensubcontracting or outsourcing the manufacturingof parts because GPS is a more precise language.Drawings based on traditional tolerancing typicallygive a lot of problems when manufacturing isoutsourced, because your supplier does not sharethe common understanding built up over the yearsbetween your design department and your in-house manufacturing. The brutal truth is that most

The brutal truth is that mostproducts function in spite of the

tolerancing, rather than because ofthe tolerancing.

products function in spite of the tolerancing, ratherthan because of the tolerancing. The realities ofmodern manufacturing have made traditionaltolerancing obsolete.

Correctly made scrap partsThe main problem is that traditional tolerancingis ambiguous. It always creates some level ofdoubt as to what exactly shall be manufactured.This ambiguity, or specification uncertainty, isoften so large that parts can be made that live upto the tolerance requirements, but will not functioncorrectly. This specification uncertainty createsboth technical and economic problems, especiallywhen the design and development departmentsand the shop that manufactures the part are farapart, as in the case of outsourcing, especially ifthey do not have a common spoken language.See example on figure 2.

Test your company’s tolerancingIn the self-check form on page 11 you will find anumber of examples of tolerance symbols andcollections of symbols that you can compare tothe drawings from your company or from yourcustomers. This way you can determine what kindof tolerancing is used in each drawing.

You can use the form on page 11 to determine ifyou are using modern GPS tolerancing. If it turnsout not to be a GPS based drawing, the conse-quence will often be that it contains significantspecification uncertainty. This can create legaland economic problems if the drawing is used forsubcontracting or outsourcing of manufacturing.

An Overview of The GPS Matrix System

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Figure 2: An example of specification uncertainty: ±tolerancing in the drawing a) is not definedon the real part. There are several different solutions (diameters) on the real part b).

The form on page 11 cannot provide any assur-ance that a drawing is correctly toleranced andhas no specification uncertainty, but it can help ingetting a rough first impression. Checking thetolerance symbols shown in the form does notrequire much technical knowhow since it only re-quires a visual comparison between the symbolsin the table and the symbols in the drawing.

Did you know:

- The traditional tolerancing language hasroots all the way back to 1930 and hasevolved significantly over the last 10 to15 years from a few standardized rulesto a comprehensive symbol language(GPS), which can simulate part function.

Specification uncertainty cancreate significant legal and

economic problems if the drawingis used for subcontracting or

outsourcing of manufacturing.

- The GPS symbol language which hasbeen developed in ISO with the input fromexperts from more than 60 countries isdocumented in over 100 internationalstandards covering more than 2500pages.

- The ISO GPS standards only function asthe dictionary and grammar book of theGPS language. They do not contain muchinformation about how the GPS systemshall be applied.

- GPS allows critical tolerances in thedrawing to be increased significantly.

- All CAD systems can be used for GPStolerancing.

- GPS applies to 2D drawings as well as3D CAD models.

- The CAD system cannot make a correctand unique tolerancing on its own ! It isonly the human knowledge andexperience that can make the tolerancingcorrect and unique using the CAD systemas a tool.

Evaluate the tolerancing in your drawings by usingthe self-check form for tolerancing shown on page11.

An Overview of The GPS Matrix System

© IfGPS 2005 4

What is the problem with traditionaltolerancing?The problem with traditional tolerancing is thatwhen the manufactured parts have non-negligibleform errors compared to the tolerances, thetolerancing becomes ambiguous and the readerof the drawing has to guess at exactly what therequirements are. See figure 2.

Tolerancing in drawingsThe primary function of drawings of products andparts is to convey the design intent and the re-quirements of the part to those responsible formanufacturing the product or the part. This isdone by focusing on the tolerancing that has beenused in the drawing.

The tolerancing shouldcommunicate all the necessaryprerequisites to ensure properproduct function. Only those

requirements that are indicated inthe tolerancing in the drawing can

be expected to be fulfilled.

It is the tolerancing, i.e. the tolerance symbol lan-guage that is used and how it is applied, that isthe important part of the drawing. See figure 3.This is because the tolerancing should commu-nicate all the necessary prerequisites to ensureproper product function. Only those requirementsthat are indicated in the tolerancing in the draw-ing can be expected to be fulfilled. There are nohidden requirements. The drawing picture itselfdoes not create requirements for the part. In par-ticular, just because the drawing picture showstwo sides of a part at a right angle to each otheror a pattern of holes arranged symmetrically, itdoes not in itself create a requirement for the pro-duced part. This often catches designers out.Because they are used to thinking based on theperfect geometry presented on the CAD screenor in the drawing, they often think there are suchimplied requirements.

Figure 3: The drawing has 3 layersdescribed in standards. Only layer 3contains the GPS symbols and thespecification requirements.

It is important to realize that thetolerancing in the drawing is the

single largest factor in determiningthe cost of manufacturing the

product or the part.

It is important to realize that the tolerancing in thedrawing is the single largest factor in determiningthe cost of manufacturing the product or the part.Unnecessarily tight tolerances drive up the costof manufacturing. If the tolerancing is made withone particular manufacturing process in mind, itprecludes the manufacturing engineer from us-ing his expertise to find the most cost effectivemanufacturing process(es) that can make partsthat will meet the functional requirements.

The tolerancing in the drawing becomes a con-tract or part of a contract when the drawing is givento another company. In this situation thetolerancing is a binding contract between the twoparties.

Traditional and hybrid tolerancingTraditional tolerancing is a tolerancing that pri-marily consists of dimensions and ±dimensionaltolerances, supplemented with surface texturerequirements. Hybrid tolerancing is a traditionaltolerancing where a few geometrical toleranceshave been added, but only as a supplement tothe traditional tolerancing.

An Overview of The GPS Matrix System

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An Overview of The GPS Matrix System

Are the drawings in your company based ontraditional or hybrid tolerancing?If so, you can, without a doubt, make better andcheaper products by using GPS tolerancing inyour technical drawings.

Ask in the design and development departmentsif GPS tolerancing is used in the drawings. If theanswer is no, there is an unrealized developmentpotential that can be unlocked by a relatively smallinvestment in training of the relevant companystaff in the use and interpretation of GPStolerancing.

A drawing with GPS tolerancing iswell suited for outsourcing of

manufacturing regardless of wherein the world the manufacturing is totake place and what language the

manufacturer speaks.

The use of modern GPS tolerancing is one of thelargest and cheapest developments that hastaken place in the manufacturing of mechanicalproducts in recent years. The use of GPS willmake your drawings unambiguous and you canuse tolerances in your future drawings that arelarger than the tolerances that you are using inyour drawings today. Finally, a drawing with GPStolerancing is well suited for outsourcing of manu-facturing regardless of where in the world themanufacturing is to take place and what languagethe manufacturer speaks.

Evaluate the tolerancing in your drawings by us-ing the self check form for tolerancing shown onpage 11 in this document.

How is GPS different?

In GPS, the symbol language has become muchmore detailed and specific. It gives the designerthe ability to make the tolerancing unambiguousand allows much more flexibility to modify toler-ance indications to express precisely what thefunctional requirements are.

Additionally, by applying GPS specifications ac-cording to the 8-step tolerancing process devel-oped by the Institute for Geometrical ProductSpecifications (IfGPS), a joint venture betweenPB Metrology Consulting in Denmark and HN Me-trology Consulting in the US, the designer canensure that all the tolerances are tied together in

one coordinate system and not allowed to "float"relative to one another. This is key, because itallows tolerances to be increased by the amountof "float" eliminated, which often can be substan-tial. However, although this 8-step tolerancingprocess is very important, it is not defined in stan-dards.

GPS tolerancing gives better profitability andbetter products.The symbol language that is used for tolerancingin drawings has been expanded, modernized, andinternationalized over the last 10 to 15 years. Themodernization and internationalization have takenplace to meet new requirements based on tech-nological developments and the needs that haveemerged in the globalization of subcontracting andoutsourcing of part manufacturing.

GPS is a natural development of the traditionalway the drawings have been toleranced for half acentury. The basis for GPS tolerancing is geo-metrical tolerancing (GD&T), but used in a newand different way.

Why do we have to implement GPS in my com-pany?GPS is necessary to ensure that the drawing canexpress the design intent unambiguously. Un-ambiguous tolerancing has become more criticalbecause tolerances have become tighter anddrawings increasingly are used for subcontract-ing and outsourcing of manufacturing.

Traditional tolerancing is only unambiguous andonly works well when the parts that are beingmanufactured have negligible form error and allangles in the part are virtually perfect, comparedto the size of the tolerances. GPS has been de-veloped to overcome this shortcoming. GPStolerancing maintains its uniqueness when ap-plied to the manufactured part even if the part hassignificant form error and angular deviations.

The basic advantage of GPS is that it allows tol-erances to be expressed more precisely and withmore detail. This means that GPS tolerancingcan simulate part function very closely. With GPSthe designer can include much more informationin the drawing. This information can be used bythe manufacturing engineer to choose the tech-nically and economically optimal manufacturingmethod.The requirements of the measurement methodare also built into the GPS tolerancing. This al-lows the metrology function to make intelligentchoices about what measurement method and

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An Overview of The GPS Matrix System

technology to use to get the right uncertainty andthe right sensitivity in the measurement. Thismeans that the existing measurement technologycan be used much more effectively and withsmaller uncertainty.

Lower manufacturing costsThe use of GPS gives a number of advantagesboth technically and economically. Parts that aremanufactured according to drawings that aretoleranced using GPS generally have lower manu-facturing cost. GPS also gives much better as-surance that the product will function accordingto the design intent, especially when the manu-facturing of the parts is being subcontracted oroutsourced domestically or across the world. Thisis because GPS tolerancing gives more informa-tion and is more precise.

Take advantage of larger tolerancesExperience has shown that traditional tolerancingforces the designer to use smaller tolerances tomake the part function, far smaller tolerances thanif GPS had been used in the drawing. This is theeconomic consequence of traditional tolerancingand it often leads to completely unnecessarymanufacturing and measuring problems.

GPS tolerancing - a technical necessityIt is crucial that readers clearly and unambigu-ously understand the drawings and what the de-sign intent is. This is the whole purpose oftolerancing!

It is most likely that your company is tolerancingin the traditional way that we all learned duringour education or later on in training courses andseminars. In this case, your drawings are prima-rily based on dimensional tolerancing for diam-eters, distances, angles etc. In some cases draw-ings may be "spiced up" with a few geometricaltolerances and surface finish requirements basedon the surface roughness parameter Ra as asupplement to the dimensional tolerancing to cre-ate what we call hybrid tolerancing.

GPS allows critical tolerances inthe drawing to be increased

significantly.

by the drawing if these symbols are used withoutknowledge of the correct meaning that they havetoday. When the symbols in the drawing are readcorrectly according to the GPS rules, the intent ofthe tolerancing will be misunderstood by thosewho know the current GPS rules and follow themcorrectly. Of course, you do not get the advan-tages that are built into the GPS system whenthe symbols are not used in accordance with themodern GPS meaning and not used systemati-cally based on the GPS philosophy.

This illustrates another very important point. Be-cause GPS is such a precise language, the needto apply revision control and quality assurance tokeep track of which standards apply to whichdrawings is much more significant than it is fortraditional tolerancing. It takes ongoing awarenessand training to keep track of revisions to stan-dards and properly implement the changes asthey occur.

It often becomes possible to morethan double the tolerance that is

indicated in the drawing when GPSis used compared to the tolerance

value that can be used in thetraditional drawing.

The introduction of GPS in the company will gen-erally provide both an economic and a technicalimprovement because the specification uncer-tainty can be eliminated completely and the cor-relation uncertainty ( a measure for how well thetolerancing simulates the intended function of thepart) can be reduced significantly. That shouldbe sufficient motivation for actively implementingGPS here and now in your company.

The specification and correlation uncertaintywhich is eliminated by using GPS can be used toeither improve the function of the part or to in-crease the tolerance that is indicated in the draw-ing or both. It often becomes possible to morethan double the tolerance that is indicated in thedrawing when GPS is used compared to the tol-erance value that can be used in the traditionaldrawing.

What does my company gain by using GPS?Some of the tolerance symbols that today are partof the GPS system are already in use in the tradi-tional drawing. There is a risk that the producedresult is quite different from what was intended

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An Overview of The GPS Matrix System

Examples of the advantages of GPS:

- There is no doubt about what the require-ments are for the part. The specificationuncertainty is low. The drawing is unam-biguous. You can communicate unam-biguously and without problems with sup-pliers both domestically and abroad evenwhen you do not have a common spo-ken language.

- The tolerances can be made more func-tionally correct. The requirements in thedrawing can be differentiated in moredetail.

- Since the tolerancing can simulate thepart function very closely, the correlationuncertainty is low.

- The drawing becomes much more valu-able for product development for the nextversion of the product since the GPSdrawing contains much more unambigu-ous information about the geometrical re-quirements of the part function.

- The tolerances are larger. Both the"saved" specification uncertainty and the"saved" correlation uncertainty can beused directly to increase the "traditional"tolerance. Larger tolerances give a bet-ter relationship between process varia-tion and tolerance and between measure-ment uncertainty and tolerance.

- The GPS drawing contains much moreinformation that can be used for morequalified choices of manufacturing pro-cesses, machining sequences, fixturing,alignment methods, etc. This means thatin many cases there is no need for sub-sequent measurements of the part re-quirements, because the requirements inthe drawing are automatically fulfilled!

- The designer no longer has to considerthe capabilities of manufacturing or mea-surement methods, but only has to con-centrate on tolerancing based on func-tion. This is the consequence of the GPSconformance principle.

- The specification operator, which is thedefinition of the tolerance symbol, deter-mines directly the theoretically correctmeasurement method. The task for the

measurement function now consists ofavoiding use of the often very expensive,slow, and complicated correct measure-ment method and equipment. Instead,the measurement function can focus ondesigning and qualifying a cheaper,faster, and simpler measurement methodthat can perform the measurement "wellenough". "Well enough" is based on ameasurement uncertainty evaluation andthe economic consequence of the uncer-tainty.

How do I implement GPS in my com-pany?

The GPS language must be implemented in thecompany based on a management decision andGPS must be used and understood by everybodythroughout the company (or within a particularproduct team), otherwise it will not work. This iswhy it is important that management is informedabout GPS and understands why it is so impor-tant to make this strategic decision.

How is GPS to be used?GPS should first and foremost be used for thecritical tolerances and requirements in a draw-ing. These are the tolerances that primarily influ-ence the function and the manufacturing cost ofthe part. It is less important that other require-ments in a drawing are unambiguous.

GPS is like a tool box: The designer can take onlythe tools that he needs and leave the rest alone.This allows the designer to learn the various speci-fication tools of the GPS system as they becomenecessary for him, once he has the basic over-view of what types of tools are available and howthe overall GPS system works.

How do we implement GPS in our company?GPS can only be used effectively after the rel-evant staff has been trained to use and interpretthe symbol language. A pilot project covering theteam responsible for a new product is a good wayto start and to gain some experience. GPS shouldprimarily be used for new drawings and newprojects. Only the problematic ones amongst theold drawings should be considered for transla-tion into GPS.

How is GPS implemented in a company?The decision to implement GPS in a companymust be a strategic decision made by topmanagement. The decision has to be very visibleto the staff as a requirement to them. Resources

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An Overview of The GPS Matrix System

Figure 4: Implementation of GPS in a company.

A pilot project covering the teamresponsible for a new product is a

good way to start and to gain someexperience.

have to be allocated because it takes time, butthe results will quickly be visible!

sufficient knowledge of the use of GPS. Mosteducational institutions have not yet added GPSto their programs and spend very few hours ontolerancing rules and symbols in the first place.

Two choicesThere are two ways to conduct the GPSimplementation process:

- self-study for everybody or in a core groupwhich then educates and informs the restof the staff.

- all staff participate in external seminarsor seminars are set up internally in thecompany with external instructors thatcreate the foundation, followed by"language" training with practicaltolerancing examples in the form ofcompleted part drawings and designs.

The first option is more theoretical than real. Itrequires too many resources and experienceshows that there is a significant risk that majorparts of the tolerancing rules will bemisunderstood.

Internal seminars are a better solution that givethe necessary foundation of common understand-ing for the implementation of GPS. This approach

ReprogrammingThe implementation of GPS (see figure 4) cannotbe done in pieces and one person or onedepartment at a time. It is necessary once andfor all to create a common “language” and acommon understanding amongst all technicalfunctions and staff within the company so theycan communicate unambiguously with each otherby using GPS. It normally requires a totalreprogramming or reeducation of all the technicalstaff within the company when the existing normaltolerancing level and the GPS tolerancinglanguage scope and possibilities are taken intoconsideration. In short, it is necessary to startover.

It cannot be expected that people that comedirectly from the education system have a

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An Overview of The GPS Matrix System

leads to the desired goal much faster and with amuch higher probability of success than the self-study method.

Teaching GPS based on the company’s owndrawingsExperience shows that there is a need for aconcentrated basic GPS seminar of at least 25 -30 hours of effective instruction time. It can consistof a review of the GPS’s Toolbox (the GPS system,the tolerancing rules and symbols) that takes up75-80% of the instruction time and should befinished with a lot of examples of how to changethe company’s own existing drawings fromtraditional tolerancing to GPS tolerancing. Theuse of the company’s own drawings as examplesis necessary because the GPS tolerancing, muchmore than traditional tolerancing, requires a verydetailed knowledge of the use and function of thepart in the product.

Experience shows that there is aneed for a concentrated basic GPSseminar of at least 25 - 30 hours of

effective instruction time.

Old problems become new solutionsAs part of the seminars, gather the participantsfrom the company in teams around a group ofproducts/parts and the related problems that theyknow and work with every day. The participantsin the teams should be combined from severalfunctions within the company (design, production,sales, purchasing, quality, measurement, etc.).This way the participants will experience duringthe seminars how they can now communicatebetter with more details and less ambiguity byusing GPS. The participants will also learn thatthey are able to solve part requirement problemsin drawings that have not previously had a goodand unique solution.

It is a good idea to invite key personnel from majorsuppliers to participate in the company’s seminars.

This will motivate the supplier and facilitate latercommunication and cooperation to everyone’sbenefit.

Getting to an operational levelThe level that can be reached with such a basicGPS seminar is not especially high nor especiallyoperative. It is certainly no “nerd level” that isreached after 25-30 hours of instruction. The levelafter this basic language class is just enough foran experienced designer to begin using GPS insimple part drawings for simple part functions.

The amount of material and the number of newthings in GPS is simply too great. But after thisseminar, the routine and the operational level isreached by systematically applying GPS.

The seminar described is appropriate fordesigners and leading personnel from othertechnical functions in the company. Operatorsfrom the production and measurement areasshould be taught GPS in a more limited seminar.

The process is expandedIt is an advantage to establish a cross functionalGPS group within the company. In the GPS group,the new tolerancing culture can then be developedafter the basic seminar(s).

It is crucial that a common understanding isdeveloped within the company of what the criticalrequirements for the parts are, because these arethe requirements where GPS must be applied.

It is advantageous to have follow-up meetingsafter the basic seminar with participation of theexternal instructor.

This can take place when there is a need in theGPS group to clarify questions about details innew drawings that are created with GPStolerancing. A more advanced discussion of thenew drawings and the understanding of the morecomplex and more advanced GPS use can takeplace at these follow-up meetings.

It is an advantage to establish across functional GPS group withinthe company. In the GPS group,the new tolerancing culture can

then be developed after the basicseminar.

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An Overview of The GPS Matrix System

The results become visibleAs it turns out, the GPS group will also lead to thedevelopment of internal company standardsbased on the new knowledge. Company stan-dards assist in collecting and documenting exist-ing special tolerance knowledge and toleranceneeds. Company standards also help in reducingthe complexity of the individual drawing. Companystandards are envisioned in the ISO-GPS sys-tem as a necessary supplement. Internationalstandards cannot and will not cover all possibilitesand details.

It is common that a need for specialized advancedseminars for smaller groups arises, for example,seminars in surface finish specification and mea-surement, form specifications and measurements,datum and datum systems, estimation and useof measurement and specification uncertainty.

Going liveThe last chance for informing all personnel, cus-tomers, and suppliers about GPS is when the firstnew GPS drawings go into production. Of course,it should ideally happen much earlier.

It is important that suppliers and personnel in thecompany’s own production departments realizethat there are now different and new symbols andrules in the drawings and especially that the rulesfor proving conformance and nonconformancenow are different from what they were and that itis now necessary to provide proof of the level ofmeasurement uncertainty.

Putting up GPS posters throughout the companyto support and inform about the new things thathappen help in raising awareness. You might alsowant to send posters and information to suppli-ers.

Hand out GPS pocketbooks to all staff (see theoverview of GPS publications that can supportGPS implementation in the company on the lastpage of this pamphlet). You can also send a GPSpocketbook written in their own language toforeign customers and suppliers.

Do not make it harder than it has to be.When GPS is initially implemented in thecompany, stay away from “old” drawings. Leavethem as they are. Start using GPS in a newproduct project. When experience with using GPShas been built up, then you can considertranslating and updating “old” problem partdrawings to GPS.

Always review old drawings from a GPS andspecification/correlation uncertainty point of viewbefore they are outsourced and sent to a supplier.Update to GPS as necessary.Maintain an overviewWhen GPS is implemented, you should alsoimplement a procedure for technical qualityassurance of the tolerancing in the drawings. Itis necessary to keep track of which and whenGPS standards and GPS rules are implemented,both now and in the future, and which drawingsand projects they apply to.

For most companies it is a new situation that the

For most companies it is a newsituation that the tolerance symbollanguage changes, develops, andimproves all the time and thereforehas to be subject to quality assur-

ance.

tolerance symbol language changes, develops,and improves all the time and therefore, has tobe subject to quality assurance.

Some advice for the futureIt is necessary to have at least one complete col-lection of ISO and/or national GPS standards inthe company. A collection that has to be kept up-to-date all the time. It should be just as natural tohave a complete and updated collection of GPSstandards as it is to have a dictionary in the com-pany. Standards are not there to teach, but onlyto give rules and tools.

The guidance and education in the use of GPSstandards must be maintained by following thedevelopments, for example, by participating inconferences or buying relevant literature or hav-ing regular scheduled follow-up seminars with ex-ternal or internal instructors.

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Question Tolerancing Symbol GPS CommentAre ±tolerances used for otherdimensions than diameters andfeatures of size in the drawing?

± tolerances are generally not unambiguous onthe real part. There is specification uncertainty.To be replaced by a position tolerance as animprovement.

Are ±tolerances used for diameterswithout using a modifier, for examplein the drawing?

A diameter without the use of a modifier is notunambiguous on the real part (see figure 2).The specification modifiers shall be used as animprovement.

Are ±tolerances used for angles in thedrawing?

± tolerances for angles are generally notunambiguous on the real part. There isspecification uncertainty. Shall be replaced byan angularity tolerance (geometrical tolerance)as an improvement.

Are ± tolerances used for coordinatesof e.g. hole centers in the drawing?

± tolerances used for coordinate tolerancing arenot unambiguous on the real part. There is avery large specification uncertainty. Shall bereplaced by position tolerances with referenceto a datum system as an improvement.

Are geometrical tolerances used in thedrawing?

If geometrical tolerances are not used, thetolerancing is solely based on dimensionaltolerancing. There is significant specificationuncertainty. Shall be replaced by GPStolerancing as an improvement.

Are datum systems used in thedrawing?

The function of the part cannot be expressedunambiguously if datum systems are not used.There is probably significant specificationuncertainty. A functionally correct datum systemshall be established as an improvement.

Is the maximum material requirementused in conjunction with positiontolerances for e.g. holes in the drawingwhen the required function is to enableassembly with the adjacent part in thedesign?

If this is not the case, parts that exceed eitherthe diameter tolerance or the position tolerance,but still function as intended (assemblypossible) will be rejected. Use the maximummaterial requirements as an improvement.

Is the 1965 version of the surface finishsymbol used in the drawing?

Very significant specification uncertainty - up to300%. Use the current GPS symbol as animprovement.

Is the 1991 version of the surface finishsymbol used in the drawing?

Large specification uncertainty - up to 30%.Use the current GPS symbol as animprovement.

Is the edge symbol used in thedrawing?

If the symbol is not used, the edges are notcontrolled. This creates specificationuncertainty. The edge symbol shall be used asan improvement.

An Overview of The GPS Matrix System

The Self Check Form

The self check form below contains a number of examples of tolerance symbols and collections of symbols that you can compare to thedrawings from your company or from your customers. This way you can determine what kind of tolerancing is used in each drawing. Theform can be used to determine if you are using modern GPS tolerancing. If it turns out not to be a GPS based drawing, the consequencewill often be that it contains significant specification uncertainty. This can create legal and economic problems if the drawing is used forsubcontracting or outsourcing of manufacturing.The form cannot provide any assurance that a drawing is correctly toleranced and hasno specification uncertainty, but it can help in getting a rough first impression.

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An Overview of The GPS Matrix System

The GPS Pocket Books

The GPS Pocket Book gives a brief presentation of the most important and the most frequentlyused tolerance symbols in GPS tolerancing. It contains 36 pages of fine print in A6 (148 mmx 105 mm) format.

The GPS Pocket Book also presents the most common rules and the most basic grammarrelated to the GPS symbol language.

The GPS Pocket Book is not intended for stand alone use. It does not give a complete andexhaustive presentation of GPS. The purpose of the GPS Pocket Book is to be a memory aidfor people who are using GPS in their daily work.

The GPS Pocket Book is intended for use together with the numerous GPS standards issuedby ISO.

The GPS Pocket Book is available in English, Spanish, German, Chinese, Swedish andDanish as of early 2005. Additional language versions are planned.

The GPS Pocket Book is an excellent aid for discussing Geometrical Product Specificationswith colleagues, clients, and suppliers around the world. Graphics and text are laid out so thesame information is in the same place on the same page in all language versions. So you canhave the English version in front of you and your supplier in China can have the Chineseversion in front of him and you can easily communicate.

The GPS Pocket Book is published by the Institute for Geometrical Product Specifications, ajoint venture between PB Metrology Consulting and HN Metrology Consulting, Inc. To purchasethe GPS Pocket Book, go to www.IfGPS.com where you can also find more informationabout the GPS Pocket Book and other GPS related materials as they are developed.

This document can be freely distributed in its entirety. Quotations can be used with indicationof the source.

An overview of

GPSA cost saving tool

See additional information about GPS on:

Outside Europe:

www.HN-Metrology.com

Henrik NielsenHN Metrology Consulting, Inc.10219 Coral Reef WayIndianapolis, IN 46256USA

Or contact:

In Europe:

www.bennich.dk

Per BennichPB Metrology ConsultingBirkevej 11DK-3500 VaerloeseDenmark

per@bennich.dk+45 44 47 01 04

hsnielsen@HN-Metrology.com+1 317 849 9577

Institute for Geometrical Product Specificationswww.ifGPS.com

An overview of GPS - A cost saving tool1st edition

2005 Institute for Geometrical Product Specifications©