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SW Tips/TricksVolume 2, Issue 2 www.triaxialdesign.com March / April 2000

Links, Equations, and Design Tables

This project demonstrates a simple tolerance analysis oftwo mating plates in an assembly. The first "pin plate"has two dowel pins pressed into each of the two holes,mating to a second "hole plate" with two holes. Thisproject will demonstrate the classic worst case toleranceanalysis where the extremes of the tolerance range foreach dimension studied will be checked against eachother in the context of the mating parts of the assembly.Tolerance analysis is not a trivial subject, therefore thisarticle will simplify the task to demonstrate techniquesutilizing various SolidWorks tools, without becomingengrossed in all of the details of the analysis. Also, try to

think of some the other ways to solve these sameproblems utilizing other tools that SolidWorks provides.Remember that there are always multiple solutions toeach part of the task. Some of these alternative solutionswill be discussed.

The goal is to determine if the two mating parts will fittogether (when the production parts are manufacturedanywhere in the tolerance range specified for eachdimension). The first step will be to model the individualparts, with special attention on the way the dimensionsand tolerances are applied to the model. Then the partmodels will be placed in an assembly and each worstcase combination will be studied. For each possiblecombination the interference and clearance between thepins and the holes will be checked.

There are three parts and an assembly that need to becreated (see Figures 1, 3, and 5). Create the "hole plate",the "pin plate", the "pin", and the assembly of theseparts. The same pin is used in both holes in the "pinplate". The outside diameter tolerance of these pins willnot be considered for this project. The plates aremodeled as simple rectangular plates 4in x 2in x 0.5inthick. The "hole plate" is the part that contains theclearance holes for the "pins". Before dimensioning theholes in a sketch, think ahead to the assembly.Specifically consider the mates that will be applied to

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I N S I D E T H I S I S S U E

1 Simple Tolerance Analysis Links, Equations, and Design Tables

4 About TriAxial Design and Analysis

Complimentary copies ofSW Tips/Tricks areindependently publishedfor SolidWorks usersworldwide.

All back issues can bedownloaded fromwww.triaxialdesign.com

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both parts. The first component in the assembly, the "pinplate", can either be fixed at the origin of the assembly,or the planes of the component can be mated coincidentto the planes of the assembly (Front to Front, Top toTop, Right to Right). Now when the "hole plate" is placedin the assembly, the planes of the component can againbe mated coincident to the planes of the assembly. Thismating simplifies the analysis of the tolerances.Dimension the holes in both plates from the center of theplates. By doing this, it is simulating the way thesecomponents will be assembled. The "pins" will center onthe holes and the alignment of the perimeter edges ofthe plates is a function of these pin and hole locations.

SolidWorks provides several good tools to use throughoutthis project. There are two holes in the hole plate thatwill vary in diameter. For the purposes of this projectboth holes will vary together. To keep the holes equal,one of several tool can be used. 1) Sketching one hole,then mirroring it to the opposite side of the part willmaintain the same diameter in both locations. 2) Addingan "equal" geometric relation between each circlecircumference. 3) Link Values to make two dimensionsequal value. This project will use Link Values toolbetween the two hole diameter dimensions.

Names for each dimension are generated as thedimensions are placed in the model. These dimensionnames make the dimension unique. These uniquedimension names are used to specify the dimensions inequations or a design table. To display these names goto the Tools pulldown menu, then pick Options, thenswitch to the General tab. In the upper left corner checkthe box for Show Dimension Names. Now when the

dimensions are visible, the dimension names will also beshown in parenthesis below the value. These dimensionscan be renamed by right selecting on the dimensionvalue, then pick Properties. The Name window shows theportion of the dimension name that can be changed to

make this name user friendly. This project has severaldimensions renamed.

Pin Plate:The distance between holes Renamed to "Distance"The distance between centerline and left hole Renamed to "Distance/2"

Hole Plate:The distance between holes Renamed to "Distance"The distance between centerline and left hole Renamed to "Distance/2"

An Equation is employed to keep the "distance/2"dimension equal to the "distance" dimension divided by2. This could have been done using mirror command

also. In other words by using a mirrored sketch circle forthe two holes, both the equal diameters and thedistances from the centerline of the part to each circlewould have been maintained (mirroring the circle mayhave been a better choice). This could also beaccomplished using a part design table. For the value ofthe "distance/2" dimension, place a formula in the cell todivide the "distance" dimension by 2.

A design table is basically a Microsoft Excel spreadsheetthat is created to organize configurations of parts andassemblies. The part design table can control all, or aportion of, your dimension values in your model for eachconfiguration of the part. The part design table can alsocontrol whether a feature is suppressed or unsuppressed.The real power of these design tables is that you can usethe entire Excel functionality in the design tables. Allfunctions, formatting, and tools are available.

The basic layout of a part design table is configurationname(s) are listed down the first column. The dimensionname(s) and feature name(s) that will be controlled are

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in the first row across the top. Then the other cells in thematrix are filled in with either values of dimensions, orthe words "suppressed" or "unsuppressed". To put a rowor column of calculations or comments that will beignored by SolidWorks, substitute "$user notes" for theconfiguration name or parameter.

Part Design Tables are used to create families ofconfigurations within a single part file. For the purposesof this project, the configurations of the part will consistof all the combinations of worst case dimensions for eachpart. Then in the Assembly Design Table we can createassembly configurations that in turn specify whichconfiguration of each part will be the active configurationfor each instance of the component in the assembly.

Configurations for all the combinations of the minimumand maximum dimension values were created based onthe tolerance values for each dimension. Figure 2 showsthe design table for the hole plate. The 2 nd through 5 th row of the design table are user to store the plus andminus values of the tolerance for each dimension (i.e.Distance plus tolerance = .005) The first configuration islocated in row 7 and is named "Nominal". For theparameter "distance@sketch2", located in column B, thevalue is 2.000 (located in cell B7). Then the additionalconfigurations down column A are all the possiblecombinations of worst case dimensions. "MaxDist withMaxHole" configuration denotes a hole plate with themaximum value of "distance@sketch2" combined with amaximum value of "holesize@sketch2". To fill in thevalues of the parameters, formulas are used. In cell B8,the formula used is =B7+C2. This takes the nominalvalue for "distance@sketch2" from cell B7 and adds to itthe "Distance plus tolerance" from cell C2, yielding thevalue 2.005. SolidWorks will only pass the final value ofthe cell for the parameter. The same method is used tofill in all of the other parameter values in this designtable.

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Assembly Design tables control various parametersrelated to multiple configurations of an assembly. Theseare extremely powerful, controlling parameters such asthe state (suppressed or unsuppressed), or the specificpart configuration name that is active of each individualcomponent instance in the assembly. The values ofparameters such as distance and angle mates can also becontrolled for each assembly configuration. This projectcreates an assembly configuration for each possiblecombination of part configurations. There are fourdifferent hole plate configurations and two different pinplate combination, so that adds up to 8 assemblyconfigurations. The syntax for the parameter to vary thepart configuration in the assembly is$confi guration@component where componentis the part name, and instance refers to the instancenumber of the part in the assembly. Figure 6 shows theassembly design table for this project. Row 4 delineatesthe first assembly configuration named "Check1". Thisconfiguration activates the "MaxDist" configuration of pinplate for instance 1, and the "MaxDist with MaxHole"configuration of instance 1 of the hole plate. Continuing

this procedure for the remainder of the assemblyconfigurations creates all the eight possible combinationsof part tolerances.

Interference detection can now be performed for eachassembly configuration. Switch to the ConfigurationManager Tab, double click on the assembly configurationto make it active. Then pick the Tools pull down menu,the pick Interference detection. Inside the top window ofthe dialog box, list the components to be checked bypicking the components either from the graphics area, orthe Feature Manager. To check the entire assembly, pickto the assembly name at the top of the Feature Manager.Then press the check button. SolidWorks checks forinterference between components and reports anyinterference it finds in the bottom window of the dialogbox. If interference is found between it also highlightsthe interference in the graphics area of the model. Thegold outline represents the actual interference, and theblue bounding box is an orthographic box that

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encapsulate the entire interference. Theaccompanying dimensions are the delta X, Y, and Zof the bounding box. Now, this info is not displayingthe solution, just showing the problem. Modeling withSolidWorks does sometimes still involve work.

For this project, when the original values shown inthe figures are used, there is interference in severalof the assembly configurations. One solution is to

increase the hole diameter in the "hole plate" to a .386. All configurations of the assembly is onceagain checked and no interference is found.

The extent this analysis even further, either theMeasure tool and/or Reference dimensions could beadded to the assembly, to determine the amount ofinterference of the amount of clearance between twoparts.

This article was written to serve as a beginningintroduction to several key SolidWorks tools that canbe used to perform this type of analysis. It is an

example of a one dimensional tolerance analysis.This analysis can be performed several other ways,and what is efficient for one company, may not bethe best procedure for the other. Good Luck, this isreally cool stuff! -(O||||O)-