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Lesson Title: Fixed - Limit Gauges
Lesson Duration: 3 hours
Industry Competencies: Participants will: identify types of fixed-limit gauges, explain the application of fixed-limit gauges,
and design both fixed-limit and functional gauges select tooling materials to meet production criteria.
Specific Objectives: Participants will: identify and describe applications for fixed-limit gauges design and fabricate to meet design specifications a practical fixed-limit gauge work collaboratively in a group or team communicate effectively using oral and written methods maintain accurate measurements in all design and fabrication projects.
Assessment(s):The following rubrics will be used in this lesson.
Multimedia Presentation RubricCompetency
or TaskHighly
Competent CompetentNeeds
ImprovementContent - Accuracy All content throughout
the presentation is accurateNo factual errors.
Most content is accurate but there is one piece of information that seems inaccurate.
Content confusing or contains more than one factual error.
Sequencing of Information
Information is organized in a clear, logical way. Easy to anticipate the next element.
Most information is organized in a clear, logical way. One slide or piece of information is out of place.
No clear plan for the organization of information.
Effectiveness Includes all material needed to give a good understanding of the topic.
Lacking a key element.Consistent with driving question.
Lacking several key elements and has inaccuracies.Completely inconsistent with driving question.
Use of Graphics All graphics attractive (size and colors) and support the topic of the presentation.
A few graphics unattractive but all support the topic of the presentation.
Graphics unattractive and detract from the content of the presentation.
Text - Font Choice and Formatting
Formats (color, bold, italic) carefully planned to enhance readability and content.
Format carefully planned to enhance readability.
Difficult to read the text material.
Spelling and Grammar No misspellings or grammatical errors.
1-2 misspellings, but no grammatical errors.
More than 2 grammatical and/or spelling errors.
Delivery Spoke at a good rate. Volume excellent for setting.
Spoke at a good rate. Volume appropriate.Good grammar.
Spoke a little faster or slower than necessary, or too quietly or loudly.
Good grammar.Maintained eye contact with audience.
Maintained some eye contact with audience.
Used unacceptable grammar. Failed to maintain eye contact. Relied too much on their notes.
Assessment Instrument - Group Work - All Group Assignments Competency
or TaskHighly
Competent CompetentNeeds
Improvement
Competency or TaskHighly Competent Competent Needs Improvement
ContributionsAlways willing to help and do more. Does more than required.Routinely offers useful ideas.
Cooperative. Works at assignments. Usually offers useful ideas.
Seldom cooperative.Does little work. Rarely offers useful ideas.
CooperationAlways listens to, shares with, and supports the efforts of others. Tries to keep people working together.
Usually listens to, shares with, and supports the efforts of others. Does not cause problems in the group.
Rarely listens to, shares with, or supports the efforts of others. Often is not a good team member.
Focus on the TaskAlmost always focused on the task and what needs to be done. Self-directed.
Focuses on the task and what needs to be done most of the time.
Does not focus on the task and what needs to be done. Lets others do the work.
Assessment Instrument - Extended Constructed Response (ECR) - Topical Statements and All Assigned Topics
Competencyor Task
HighlyCompetent Competent
NeedsImprovement
Context and Argument Context appropriate.Argument satisfactory. Clearly stated thesis included.
Context appropriate.Argument satisfactory.
Context inappropriate.Argument unsatisfactory.
Evidence Abundant, relevant specifics (names, events, legislation, court decisions, etc.) provided. Includes obscure, but important evidence. Thorough chronology.
Ample and appropriate evidence provided.
Evidence is largely missing or generalized.
Analysis Well-reasoned cause and effect arguments.Fully explained con-clusions. Refers to views of others.
Organizes argument and uses data to support conclusions. Recognizes causation, change, and continuity.
Minimal analysis or fallacious reasoning.
HistoricalAccuracy
Virtually error free; minor mistakes do not compromise argument.
May have a few errors. Mistakes may slightly hinder argument, but do not detract from the overall accuracy.
Many errors.
Thoroughness Covers all areas of Covers entire question, Covers question
question in approximate proportions to their importance.
but may be slightly imbalanced.
superficially. May not complete all tasks.
Presentation Uses clear, appropriate and precise language.Cohesive organization.Very few grammatical errors.
Uses clear language.Well organized.Contains few grammatical errors.
Inconsistent organization. Grammatical errors cloud argument to a major degree.
Assessment Instrument - Class Seminar for All Scheduled MeetingsCompetency
or TaskHighly
Competent CompetentNeeds
ImprovementParticipation Active level of
participation, offering solid comments and ideas but not over-bearing, allowing others to engage in discussion.
Adequate participation offering valuable comments at times, with only occasional interruption of others.
Unacceptable interaction and participation with numerous interruptions or off-topic discussions.
Contribution Comments and ideas are of high value and enable more intense discussion of seminar topic.
Comments are appropriate and on topic, with some ideas of high value, enabling good discussion of seminar topic.
Rarely offers appropriate comments and seeks to disrupt the meeting.
Cooperation High level of courtesy towards others facilitating engaging and topical discussion on selected topics.
Appropriate level of courtesy towards others enabling good discussion on seminar topic and little disruption observed.
Exhibited little courtesy towards others through inappropriate comments and behavior during meeting.
Topic Focus Comments are always focused on seminar topic, including questions and discourse with others during entire meeting.
Comments usually on target and appropriate, including questions and topical discourse during entire meeting.
Not focused on topic and seeks to disrupt with inappropriate questions and comments throughout the meeting.
Assessment Instrument - Journal (Daily Entries Required)Competency
or TaskHighly
Competent CompetentNeeds
ImprovementOrganization Journal contains a
chronological sectionas well as sections for sketches, reference sources, people, business contacts, etc.
Parts of the journal show organization,however some parts are mixed into other sections.
Journal is sloppyand/or haphazardlyorganized.
Daily Entries Details of information gathered and/or workaccomplished for each day is entered.
Journal is missing a few daily entries.
Journal is missingmany daily entries.
Content Journal entries aresufficiently descriptive to completely recreatethe daily accomplish-
Most information isdetailed howeverimportant detailsare missing to
Journal entries areinsufficiently descriptive tocompletely recreate the
ments. complete the task. daily accomplish-ments.
ProperCitation ofJournals!Books!Videos!Websites
Has APA approveddocumented citations of all sources in thejournal and infor-mation is documented properly.
All information is documented and some sources are incorrectly cited.
Some sources aremissing and othersources are incorrectly cited.
Drawingsand Sketches
Journal containssketches and drawings that are related to the topic and express what will be created.
Sketches are drawnexplaining the topic but are poorly done.
Quantity of sketches and drawings areinsufficient to explain the topic.
ReferencingMaterials(Note Cards)
Note cards containparaphrased infor-mation from source and cited reference.
Note cards missing some citations ofsources.
Note cards haveincomplete information and lack citations.
PhoneConversationAbstracts
Phone conversations are documented for:contact, phonenumber, information,company, address,date.
Most informationrequired is complete.
Missing information vital for calling backcontacts.
BusinessContacts
Lists business contacts including addresses, phone numbers, e-mails, company, faxnumbers, discussionexists.
Has all contacts but information is missing.
Some contacts aremissing and infor-mation is missing.
Assessment Instrument - Research Paper for All Assigned TopicsCompetency
or TaskHighly
Competent CompetentNeeds
ImprovementTimeliness The participant has
sub-mitted the final version of the research paper on time.
The participant has sub-mitted the final version of the research paper one day late.
The participant has sub-mitted the final version of the research paper one week late.
Content-Whole Paper
The participant's papercontains all contentsections required by the teacher. Sections on Introduction, Identifying the Problem, InitialResearch, The Proposed Solution, Researching theSolution, Prototyping, Testing, Evaluating test results and data, and a conclusion are most common.
The participant is missing only one section which was applicable to theresearch project.
The participant was missing multiple sections, or sections expected to be separate were combined.
Content -Within EachSection
Each section of the paper contains the material appropriate
There are minoroccurrences whereinformation is placed
Large quantities ofinformation areplaced in sections
for that section.The sections are cross-referenced where necessary. No material is misplaced.
in a section in which it does not belong, or sections do not refer to other sections where it would make sense to do so.
inconsistent withthe purpose of thesection.
Organization Within each section, the material presented is very clearly organized. Discussion progresses along lines of logic. Readability is facilitated by crisp organization of thoughts.
Within each section,material is presentedin a fairly wellorganized manner,but there are someitems which seemmisplaced. Eachsection still followsan outline.
Evidence oforganization, butwith serious flaws.Decisions discussed without backgroundinformation.
LanguageMechanics
Free of spelling,punctuation, andgrammatical errors.
Minimal occurrences of spelling, punctuation, and grammatical errors.
Distractingly frequentoccurrences ofspelling, punctuation, and grammatical errors.
TechnicalAccuracy
The technical content of the paper is without flaw. Exacting care has been given to ensure facts, data, and results are stated in a technically correct manner. Numerical quantities are given proper units. Calculations are properly documented and executed.
Minor technical flaws exist in words, units, or calculations, but these do not detract from the overall points made by the author.
Numerous minortechnical flaws exist. Units are ignored or misused. Overall credibility of the author's proficiency isdamaged.
References Referenced material is annotated in proper APA or MLA style consistently through-out. Works Cited page is in correct format.All items requiring citation are properly cited.
A few minor errorsor omissions exist inthe referencing ofothers' work.
Numerous minor orsome major errorsor omissions existin the referencingof others' work.
Appendices(if appropriate)
The paper includesappropriate appendices to support the text of the paper. Appendices are referenced in the text of the paper.
Bulky amounts ofinformation or draw-ings are included in the main body of the paper itself, rather than in the appendix. References missing or in error.
Some appendix infor-mation provided, but it is obviously incomplete.
Assessment Instrument - Oral Presentation for All Assigned TopicsCompetency
or TaskHighly
Competent CompetentNeeds
ImprovementOrganization Participant presents
information in logical, Participant presents information in logical
Audience has difficulty following presentation
interesting sequence which audience can follow.
sequence which audience can follow.
because participant jumps around.
Subject Knowledge Participant demonstrates full knowledge (more than required) by answering all class questions with explanations and elaboration.
Participant is at ease with expected answers to all questions, but fails to elaborate.
Participant is uncomfort-able with information and is able to answer only rudimentary questions.
Graphics Participant's graphics explain and reinforce screen text and presentation.
Participant's graphics relate to text and presentation.
Participant occasionally uses graphics that rarely support text and presentation.
Mechanics Presentation has no misspellings or grammatical errors.
Presentation has no more than two misspellings and/or grammatical errors.
Presentation has three or more misspellings and/or grammatical errors.
Eye Contact Participant maintains eye contact with audience, seldom returning to notes.
Participant maintains eye contact most of the time but frequently returns to notes.
Participant occasionally uses eye contact, but still reads most of report.
Elocution Participant uses a clear voice and correct, precise pronunciation of terms so that all audience members can hear presentation.
Participant's voice is clear. Participant pronounces most words correctly. Most audience members can hear presentation.
Participant's voice is low. Participant incorrectly pronounces terms. Audience members have difficulty hearing presentation.
Resource(s):
Print Materials - Campbell, Paul. Basic Fixture Design. New York: Industrial Press, 1994. Carr Lane Manufacturing. Jig and Fixture Handbook. St. Louis, MO: Carr Lane Hoffman, Edward G. Jig and Fixture Design, 4th ed. Albany, NY: Delmar, 1996. Nee, John G., et al. Fundamentals of Tool Design, 4th ed. Dearborn, MI:
Society of Manufacturing Engineers, 1998
Audiovisual -Internet sites - www.tmanet.com/
www.jppattern.com www.tmanet.com/industry/all.aspwww.ntma.org
Key word search - tooling for manufacturing, tooling, jigs and fixtures, machine operation tooling, tool and dies, tooling solutions, fixed-limit gauges, gauges for manufacturing, gauges.
Purpose of the Lesson:Participants will be introduced to the purpose and design of fixed-limit (go-no/go) gauges to ensure accuracy and quality in production work.
Required Knowledge and Skills: Participants will: use basic properties of angles and triangles explain the importance of applying geometric dimensioning and tolerancing
(GD&T) early in the product realization process examine advantages and disadvantages of appropriate measurement methods, and
interpret measurement data regarding quality of conformance demonstrate basic skill in the production of product design drawings as
represented in three dimensions in a Computer Aided Drafting and Design (CADD) system
demonstrate safe operating procedures for each machine tool used develop a list of material-cutting operations and identify the sequence needed to
make a specific product use hand tools to support the setup and operation of material-cutting machinery operate lathes, drill presses, milling machines, and horizontal and vertical
bandsaws at an introductory level select cutting speeds and feeds and calculate the RPM appropriate to a specific
material/cutting tool combination link the basic theory of material cutting to tool geometry (chip formation) apply basic precision measurement instruments before, during, and after material
removal operations to ensure that product specifications and tolerances are met describe the relative motions of the machine and the interactions of various
subsystems, including the machine tool, machine controls, drive mechanisms, cutting tools, tool holder, workpiece, and workholder.
Tools, Materials, Equipment Needed: 2-4 tool catalogs (most current possible) computer lab with internet access and CADD software 1 lathe or drill press (both can be used) bar stock (if using lathe) 1 pin library (good resource for gauge solutions)
Specific Safety Requirements:Each lesson includes specific information about appropriate safety procedures, as well as any necessary instructions for the disposal of materials used. Participants should always wear safety glasses when engaging in laboratory activities. In addition, anyone using equipment should be familiar with the operating instructions provided by the manufacturer of that equipment and should follow safe and proper operating procedures at all times.
Lesson Elements: (5-E Model)
Engagement:Participants should be presented with an object that they use frequently and value for this initial discussion. To begin this exchange, we suggest that a skateboard be used to generate participant interest. A few examples of skateboards could be provided by the instructor by asking participants to bring in one if they own one. Sports and hobby shops are eager to provide examples to teachers for such objects if they feel participants may find their products worthy and become a regular customer. Either way, a product that participants find interesting should be used. After examining the product, in this case, a skateboard, participants will describe the following.
ProductPrimary Material
SizeL x W x H
Weight / Mass
FinishUnique
FeaturesSkateboard 1
Once the chart is completed and participants have made some basic comparisons for a variety of similar products - Skateboards, the instructor can lead a discussion about the varying features of the products and carefully help participants realize the very distinct or unique features for each. Participants should be asked a very basic question about the manufacture of such products.
What are the critical measurements that must be made for such similar products?
The instructor should record participant responses on a highly visible chart. A discussion should reveal common responses and of course any differences. The idea is to get participants to agree that there are common critical measurements for similar products. If you just start with a primary part such as the skateboard footboard or "deck" which holds the rider, then, those basic sizes can be compared and agreed upon as important measurements that must be maintained within high tolerances.
There may even be specific sport requirements for various skateboards that influence key measurements. It is suggested that the focus for skateboards be the "decks" and their varying size. These should be explored carefully.
Other components that can be compared in skateboard design include the following:
TRUCKS….
WHEELS…..
BEARINGS….
Participants should be asked the following after a basic review of the product and key components such as those presented above for skateboards.
What type of device or measuring tool can be used to ensure that every "DECK" on a particular skateboard be exactly the same or fall within the required tolerances during production of that part?
Participants should offer their ideas with basic engineering sketches to help clarify to others in the class.
Exploration:Participants should be presented the 5-step process to determine a gauge size. This process review and discussion about the value of gauges to ensure product part size will be the first step during exploration of this lesson topic.
FIVE-STEP GAUGE SIZE PROCESS
When designing a measuring method for a product, follow the same steps as for any tool or fixture. For gauging, the information you will gather is slightly different from the information needed for a fixture or jig, but the method is the same:
1. Gather product information: In the case of gauging, product information usually includes the features and tolerances to be measured. Also identify the process that the tool will perform. Will the measurement be a pass/fail inspection, or is more data required for analysis?
2. Determine on which machine the part or tool will be used: Determine the needs of the operation. Is it a high-volume operation that requires a very quick measurement? Does the operator need feedback in the form of data so that he or she can control the process? How often will the measurement be made? Will every part be measured, or can a sampling of all parts be used to determine overall quality?
3. Describe the machine operation including safety, loading and unloading, and "mistake-proofing": Is this measuring method practical, given the product information? Are special instructions needed for the gauge to prevent mistakes in its use?
4. Consider tooling costs, changeover, and tolerances: High-precision gauging can be very expensive. Are the product specifications likely to change, thereby causing the gauge to become obsolete? Can the gauge be used for other products or processes, or is it dedicated to one job?
5. Evaluate and inspect the tool: This last step usually involves evaluating the product coming off the tool or jig. For gauging applications, evaluate the answer you are getting from the gauge. Is it really measuring what you want to measure? Are you getting a meaningful answer from the measurement? Will you be able to make a decision to accept or reject, based on the use of the gauge?
The following is offered as background information for fixed-limit gauges.
Probably the most common and easiest tools to use are fixed-limit gauges. Also referred to as fixed, plug, or go/no-go gauges, these tools mimic the mating part. Go/no-go gauges are commonly used to check the size of a hole. In this application, the gauge would consist of two precision cylinders made to the upper and lower limits of tolerance of the hole. The go gauge is close in size to the low tolerance limit.
As long as the hole is not undersized, the go pin will enter the hole. A no-go pin, made to the upper limit of size, is used to ensure the hole is not oversized. As long as the hole is
Master setting disc
not too big, the no-go pin cannot enter the hole. Go/no-go gauges are quick and easy to use, and they tend to be relatively inexpensive. Since they usually give a yes or no answer, different operators should obtain the same results. Small - diameter plug gauges are also called pin gauges.
It is always better to challenge participants to do some investigation on their own about specific topics in manufacturing rather than simply offer the information via reading. A combination of reading and resource review is a better approach. It is suggested that participants begin with an internet review to obtain basic information about go-no/go or fixed-limit gauges. Participants could then compare what they find with the information provided to the instructor in the chart below.
There are many different types of go/no-go or fixed-limit gauges. The following table illustrates several different kinds of fixed-limit gauges.
CategoryDesignation and Sketch of
Typical GaugeDimensions and
Condition Gauged Application ExamplesMaster gauges Nominal dimension or
limits of gauging rangeSetting comparator type measuring instruments, calibrating air gauges, adjusting micrometers, checking limit gauges
Limit length gauges(rigid or adjustable)
Single length dimension or diameter
Checking the diameter of round external or internal features, or the distance between parallel boundary surfacesGauging carried out by using sequentially the go an the no-go gauges of the toleranced dimension
Cylindrical limit gauges
Maximum and minimum material condition of basically round partsGauging extends over an annular tolerance zone
Inspecting the combined effect of dimensional variations and geometric irregularities of nominally round inside and outside surfaces
Geometric form gauges
Regular geometric forms individually or in combination with size
Checking straightness, perpendicularity, etc. with straight edges, squares used with geometric bodies, such as a cone with taper gauges
Adjustablelimit plug
gauge
Adjustablelimit snap
gauge
Cylindrical limit plug
gauge
Cylindrical limit ring
gauge
Taper pluggauge
Taper ringgauge
CategoryDesignation and Sketch of
Typical GaugeDimensions and
Condition Gauged Application ExamplesMultiple dimension gauges
Features whose adequacy is determined by the combined effect of several parameters
Threads, serrations, splines, etc. whose feature form, the sizes of the critical dimensions, and their relative locations must be checked to determine their cumulative effect on the effective size
Contour gauges The conformance of object contour with the gauge contour
Checking radii, fillets, screwed thread pitch, gear contours, etc. by mating the gauge with the object and then observing the condition of coincidence (either directly or by means of optical magnification)
Assembly gauges Size and geometric form of individual surfaces, as well as their inter-relations such as coaxiality, alignment, and so on
Housings with several coaxial bores; size, alignment and location or keyways; indexing positions of grooves and so on
Participants should investigate the following types and present their findings to the class via oral and written forms.
Types of Fixed-Limit Gauges
Snap GaugesThe adjustable-limit snap gauge can be adjusted by setting the length between the two pins at each end of the gauge. A snap gauge is usually set against a gauge block or master gauge. Even though the gauge can be adjusted, a snap gauge can be thought of as a fixed caliper. It is called a snap gauge because the gauge “snaps” past the go length and stops at the no-go length. The positive "snap" tells the operator that the gauge has passed the go length, has stopped at the no-go length, and indicates an acceptable part.
Plug GaugesThreaded plug gauges and threaded ring gauges are preferred for measuring threads. The go and no-go members of threaded gauges are made with low and high pitch diameters. It is very easy to tell by using threaded gauges if a thread is made correctly. Again, the
Limit threadgauge ring
Male
Limit threadgauge plug
Female
Radius gauges (templates)
Assembly gauge for coaxial bores
threaded plug and ring gauges imitate the part in the assembly. If the gauge "goes," so should the mating part.
Master GaugesMaster gauges are used to set other gauges or measuring devices. Master gauges are usually not used to inspect products. Due to their high precision, extra care is used to minimize wear on these expensive tools.
Tolerance ClassesLike products, gauges have tolerances on their permissible size. For example, plug gauges are produced at different levels of precision, or classes. Each class has a different tolerance, called the "gaugemaker tolerance." The following table shows the gaugemaker tolerances recommended by the American Gauge Design Commission (AGDC). As gauge diameters increase, tolerances also increase, due to the inherent difficulty of making large diameters perfectly round and straight.
XX-class gauges are ground and lapped and are used primarily as masters. X-class gauges are precision-lapped and used for very close tolerance features. Y-class gauges are also lapped but are used less frequently than Z- or X-class gauges, due to typically small price differences between Y- and X-class gauges. Z-class gauges are ground and polished, with grinding marks often still visible.
Many shops have sets of Z-class plug or pin gauges. These sets are available in increments of 0.001 in. or 0.02 mm and are made to a plus and minus tolerance. For example, one set (or “pin library”) may contain all the gauges between 0.060 to 0.250 in increments of 0.001.
Within the set, each gauge is marked with its nominal size and a plus or minus to indicate which way the gaugemaker tolerance is applied. Plus gauges are used as go gauges,
Gaugemaker Tolerances for Cylindrical Plug and Ring Gauges(in inches)
while minus gauges are used as no-go gauges. Pin libraries are useful for quickly assembling a go/no-go set or for determining the size of a hole. Be sure to consider company policy on gauging tolerance when using a Z-class library.
Plug gauges are available in several styles. The styles are different in that each is attached to a handle in a different way. The following table illustrates the most common types of cylindrical plug gauges and ring gauges.
Applicable for Size Range Designation Sketch Description of the Design
0.030, to and including 0.760 inch
Wire type plug gaugedesign
The wire type members of the gauge are held in a collet-equipped handle which firmly retains the gauging wire in a more or less extended or reversed position
Above 0.059 inch, to and including 1.510 inch
Taper lock plug gaugedesign
The gauging member which has a taper shank which is forced into the taper hole of the handle, resulting in a dependably rigid gauge. A drift hole permits the removal of the gauging member from the handle.
Above 0.760 inch, to and including 2.510 inches
Reversible ortri-lock
plug gaugedesign
The end faces of the handle have three radially-arranged wedge-shaped locking prongs which engage the corresponding grooves on the face of the gauging member. Both faces of the gauging member have similar grooves, permitting the plug to be reversed when worn. A single through screw secures the meshing wedge elements, causing them to stay in a rigidly locked position.
Above 2.510 inches, to and including 8.010 inches
Above 8.010 inches, to and including 12.010 inches
Annularplug gaugedesign
Weight reduction of the large size gauges (to the limit consistent with stability) is the leading objective of this design, consisting of a rim as gauging member and an integral web for ridgity. The center of the web is bored out to reduce weight; threaded holes in the retained section receive ball handles.
Have participants read the following and ask them to generate at least three questions from this reading. The instructor should lead the discussion about this information with participants sharing their questions. Questions from participants can be presented to others in class with an exchange of answers validated by the original group. This sharing will generate more enthusiasm about the topic and instructional value.
READING PASSAGEEvery company has a policy about the use of plug or fixed-limit gauges. Because gauges are never perfect, company management decides how much of the product tolerance can be used up by the errors in the gauge. For example, suppose you have a 1.000 inch hole with a ±0.0005 inch tolerance (a total tolerance of 0.001), and you want to use a Z-class go/no-go gauge. From the gaugemaker tolerance table, you see that the gaugemaker tolerance on a 1.000 Z-class pin is 0.00012. If both the go and no-go gauges are made at the limit of their permissible size, the gauge will use 0.00024 inches of product tolerance. In other words, 20% of the product tolerance is used up by the gauge. This may or may not be acceptable, and the company gauging policy should help in making the decision. If 20% is too much, a more precise (and expensive) class of gauge can be used. In this example, a XX-class gauge will use only 6% of the product tolerance.
Many companies use the Rule of Ten, which means that the measuring device should be 10 times more accurate than the tolerance it is trying to measure. Or, to look at it another way, the tool may not use more than 10% of the tolerance of the part. Similarly, the Rule of Five would not allow the tool to use more than 20% of the tolerance of the part, and the Rule of Four would restrict the tool to using not more than 25% of the tolerance of the part.
Many companies have a policy stating that fixed-limit gauges should never accept out-of-tolerance parts. Although this seems obvious, it is important to remember when determining the direction of the gaugemaker tolerance. It is common industrial practice to apply a plus tolerance to go gauges and a minus tolerance to no-go (plug) gauges. However, ring and snap gauges apply the minus tolerance on the go gauge and apply the plus tolerance on the no-go gauge. This practice ensures that the company always risks rejecting good parts instead of accepting bad ones. This type of policy is called the unilateral system because the gaugemaker tolerance is allocated in one direction around the part tolerance. A bilateral system would apply the gaugemaker tolerance in plus and minus directions from the limit of the part tolerance.
Formulas and Rules discussion (this should be read also by participants):
Use the following formulas to determine the size of go/no-go plug gauges to measure holes. (To determine the size of ring gauges, the go and no-go gauges would be reversed.)
Total gauge tolerance = total part tolerance, multiplied by the percentage allowed by policy for gaugemaker tolerance.
From this total, determine the class of gauge to use.Go plug size = minimum part size (lower limit), with gaugemaker tolerance applied in the plus direction.
No-go plug size = maximum part size (upper limit), with gaugemaker tolerance applied in the minus direction.
Example: For a 1.0000 ±0.0005 hole, specify the plug gauge size and gaugemaker tolerance for a set of go/no-go gauges so that no more than 10% of the hole tolerance is used by the gauges. Use the unilateral system to apply gaugemaker tolerances.Determine the permissible gaugemaker tolerance (specified by company policy).
In this case, it is 10%. 10% of 0.001 = 0.0001, so the gaugemaker tolerance may not be greater than 0.0001.
The table of gaugemaker tolerances shows that an X-class gauge for this size diameter has a tolerance of 0.00005. An X-class gauge is acceptable for both gauges since their total error will not be more than 0.0001.The go gauge will be specified at the low limit of the hole size, with a plus gaugemaker tolerance:
minimum hole diameter = 0.9995 go gauge diameter = 0.9995, +0.00005, -0. The no-go gauge will be the upper limit of the hole diameter, with a minus
tolerance maximum hole diameter = 1.0005 no-go gauge diameter = 1.0005 +0, -0.00005
If a hole were made to its exact upper limit (1.0005), and if the no-go gauge were made to its lower limit (1.00045), the part would accept the no-go gauge and be rejected even though it is within tolerance. Rejecting good parts is usually more acceptable than failing to reject bad parts. If the parts are expensive, additional and more precise measurements may be made.
The bilateral system uses the same calculations, but the tolerance of 0.00005 is applied to the gauge as a plus or minus. If the part is oversized at 1.00053 and the no-go gauge is at its upper limit of 1.00055, the part would pass the no-go inspection even though it is out of tolerance. Most companies would consider this unacceptable.
Gauge Materials - (To be presented to participants for reading and discussion with their questions generated from the reading.)
The two most important material properties for gauge applications are dimensional stability and wear resistance. Fixed-limit gauges can be made from carbon tool steels that are air- or oil-quenched, such as A-2 or O-1.
For example, chrome-vanadium alloys are often used for plug and pin gauges. Gauge manufacturers extensively heat-treat their alloys so that the gauges will not change over time. In some cases, raw materials are aged for 10 years between heat-treating and finish-sizing.
Very high-wear applications may require more expensive materials or processes, such as chrome plating or titanium nitride coatings. Solid tungsten carbide gives excellent wear resistance but is very expensive. Tungsten carbide is also very brittle and can be broken easily, especially when using very small diameters.
In anticipation of wear, some percentage of the gaugemaker tolerance may be added to the nominal size of the go gauge, making it slightly bigger. For example, if the gaugemaker tolerance is 0.0001, you might apply half of that amount (0.00005) for wear. You would therefore add 0.00005 to the nominal size of the go gauge and allow a plus gaugemaker tolerance of 0.00005.
A wear allowance is usually not applied to a no-go gauge as it is not expected to enter the part.
Explanation:Participants should address the following:
1. What are the costs, advantages, and disadvantages for using fixed-limit gauges?2. What information can be obtained through the use of fixed-limit gauges?3. Discuss gauge operator skill as a critical factor for reliability.4. Would you expect different types of gauges to produce different results? Why? In
what ways?5. What do fixed-limit gauges tell us?6. Participants should provide examples of their solutions for fixed-limit gauges
required during the extension portion of this lesson. Based on problem requirements and design constraints, participants should present their final design solution with a multimedia presentation that describes key details and challenges in their solution.
Extension:Participants will now be challenged to design and fabricate a basic go/no-go or fixed-limit gauge to address a specific machine operation for a product part or component.
Refer to Engineering Drawing: Robotic Gripper Base and design a set of plug gauges to inspect the 0.343 through diameters.
Assume that this company uses no more than 5% of part tolerance for its gauging policy.
Use the unilateral system of tolerancing. Make no allowance for wear.
1. Determine the correct gaugemaker tolerance and class of gauge needed.2. Determine the correct size of the go and no-go members.3. Specify the appropriate gaugemaker tolerance to both members.4. Research the cost of buying the specified gauges in the appropriate class.5. Specify the material to be used in making the gauges.
Refer to Engineering Drawing: Robotic Gripper Base: see above
Design a set of plug gauges to inspect the 0.343 through diameters. See image above.
Assume that this company uses no more than 5% of part tolerance for its gauging policy.
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Use the unilateral system of tolerancing. Make no allowance for wear.
1. Determine the correct gaugemaker tolerance and class of gauge needed. From the print: title block tolerance on the 0.343 diameter hole = ± 0.001, 0.002 total gaugemaker tolerance is to be 5% of 0.002 = 0.0001 From the table of gaugemaker tolerances, total tolerance of 0.0001, X-class tol = 0.00004 Total tolerance from both gauges = 0.0008, therefore X-class gauge is acceptable
2. Determine the correct size of the go and no-go members. Go member = lower hole size limit = 0.342 No-go member = upper hole size limit = 0.344
3. Specify the appropriate gaugemaker tolerance to both members. Go member = lower hole size limit + gaugemaker tolerance = 0.342 +0.00004, -0 No-go member = upper hole size limit - gaugemaker tolerance = 0.344 +0, -0.00004
4. Research the cost of buying the specified gauges in the appropriate class. (Use any available tool catalog to look up the cost of the specified gauges.)
5. Specify the material to be used in making the gauges.
Participants should move forward with fabrication of the following using available machines. This can be adjusted to meet local equipment inventories per instructor need.
If a machine shop is available: Refer to Engineering Drawing: Robotic Gripper Base – (shown above)
1. Determine the correct gaugemaker tolerance and class of gauge needed, using the Rule of Five.
2. Determine the correct size of the go and no-go members.3. Specify the appropriate gaugemaker tolerance to both members.4. Using a lathe, turn and polish the correct diameter on two lengths of mild steel bar
stock.5. Measure the finished gauges.
Calculate the percentage of part tolerance which both gauges use, based on their actual size.
Subtract the measured size from the actual size. Divide the result by the total tolerance.
Multiply the quotient by 100 to get the percentage. Example:
Measured size = 0.34250.3425-0.342 = 0.0005(0.0005 / 0.001 x 100 = 50% of tolerance used by this gauge
Evaluate the likelihood of accepting good parts or rejecting bad parts.
50% of tolerance used by the gauge-error will result in many good parts being rejected. This is not good for high quality production. Participants must be aware of this calculation and the percentage that would be acceptable.
If a pin library is available: Refer to Engineering Drawing: Robotic Gripper Base
If a PIN library is available, complete the following:1. Determine the correct gaugemaker tolerance and class of gauge needed, using the
Rule of Five.2. Compare Z-class gaugemaker tolerance to Rule of Five tolerance.3. Select the correct gauges from the pin library.4. Measure the gauges you selected.
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Calculate the percentage of part tolerance which both gauges use, based on Z-class tolerance.
Determine the likelihood of accepting good parts or rejecting bad parts.
Again, if a PIN library is available, participants should address the following: (Use Robotic Gripper Base Drawing above.)
1. Determine the correct gaugemaker tolerance and class of gauge needed, using the Rule of Five.From the print: title block tolerance on the 0.343 dia. hole = ±0.001, 0.002 total Gaugemaker tolerance is to be 20% of 0.002 (Rule of Five) = 0.0004 From table of gaugemaker tolerances, total tolerance of 0.0004, Z-class tolerance = 0.0001 Total tolerance from both gauges = 0.0002, therefore Z-class is acceptable.
2. Compare Z-class gaugemaker tolerance to Rule of Five tolerance. Tolerances are the same.
3. Select the correct gauges from the pin library. Select a 0.342 plus pin and a 0.344 minus pin.
4. Measure the gauges you selected.
a. Calculate the percentage of part tolerance which both gauges use, based on Z-classtolerance. Subtract the measured size from the actual size. Divide the result by the total tolerance. Multiply the quotient by 100 to get the percentage.
Example:measured size = 0.3422 0.3422 - 0.342 = 0.0002 (0.0002 ÷ 0.001) x 100 = 20% of tolerance used by this gauge
b. Determine the likelihood of accepting good parts or rejecting bad parts. 20% of tolerance used by the gauge-error will result in some good parts being rejected.
Finally, compare the cost of an X-class gauge to the cost of a rejected part.
Evaluation:Rubrics for the following are available.
Written and verbal communication Multimedia presentations All measurements (US and SI) Research Group work
Unique to this lesson, the following rubric is offered to guide fixed-gauge selection, design and application:
Assessment Sheet: Fixed-Limit Gauges
Participant: Date:
Use the following rubric to evaluate the participant's performance.
ParticipantDeliverable
HighlyCompetent
Competent NeedsImprovement
Identify and selectFixed-Limit Gauges
Correct tolerance and class of gauge are chosen; correct percentage is calculated. Go and no-go sizes are correct, and correct tolerance is specified. Cost is researched and recorded.
Incorrect tolerance or class of gauge is chosen; incorrect percentage is calculated. Go and no-go sizes are incorrect, or correct tolerance is not specified. Cost is not researched and recorded.
MachiningFixed-Limit Gauges
Correct tolerance and class of gauge are chosen; correct percentage is calculated. Go and no-go sizes are correct, and correct tolerance is specified.
Incorrect tolerance or class of gauge is chosen; incorrect percentage is calculated. Go and no-go sizes are incorrect, or correct tolerance is not specified.
MachiningFixed-Limit Gauges using a Lathe
Lathe work is correctly and professionally done; calculations are correct, and prediction of acceptance/rejection is identified and evaluated correctly and completely.
Lathe work is correctly done, calculations are correct, and prediction of acceptance/rejection is correct.
Lathe work is not completed or is incorrect; calculations are incorrect; or prediction of acceptance/rejection is not identified or is not evaluated.
Comments:
Enrichment:
Have participants select a specific fixed-limit gauge and prepare a schematic or drawing using an available CADD program and present their drawing and description of the gauge to the class. Examples are shown below for possible choices. There are many that participants could choose from after they investigate numerous gauge designs and applications.
