Activity 2.3.2: Parametric Constraints Answer Key

Activity 2.3.2 – Parametric Constraints Answer Key

Purpose Have you ever received an advertisement in the mail that looked like it was tailored specifically for you? How could the company afford to spend so much time and money entering your name and other personal information into the various locations of the advertisement? The answer is the company took your personal information that it has within a database, and had a computer plug specific pieces of your personal information into various locations of a generic document that was set up with links to the database. The same thing happens with email advertisements. This type of work takes a great deal of preplanning to pull off, but the efforts are worth it if a number of customers respond.

Engineers perform similar types of plug and produce operations, specifically in the area of 3D CAD solid modeling. Numeric constraints, also referred to as parametric dimensions, may not always have a fixed number value. Some objects must be customized, like a tailored suit or dress. If you were to return to one of your elementary school classrooms, you would think that someone took normal sized furniture and uniformly scaled it down. That could very well have been the case. If designed correctly in a 3D CAD solid modeling program, the furniture that you interact with as a young adult can be scaled down by changing one or more dimensions. Companies are beginning to build this type of design flexibility into their internet-based customer ordering systems. If the customer enters specific dimensional values, colors, and sometimes materials into the online database, the computer updates the sizes and features of the various associated parts and places and delivers an order to the company staff. This is only one example of the power of parametric modeling.

Equipment  Computer with 3D CAD solid modeling software  Engineer’s notebook  Number 2 pencil

Procedure In this activity, you will learn how algebraic formulas can be used to replace numeric values in a 3D CAD solid model.

Project Lead The Way, Inc. Copyright 2007 IED – Unit 2 – Lesson 2.3 – Activity 2.3.2 – Parametric Constraints Answer Key– Page 1 Project Lead The Way, Inc. Copyright 2007 IED – Unit 2 – Lesson 2.3 – Activity 2.3.2 – Parametric Constraints Answer Key– Page 2 Study the images on the previous pages, and table below. Use the given information to calculate the missing values. Create the object in a 3D CAD solid modeling program using the dimensions and parametric equations provided. The only numeric value that you should enter is 3 inches for dimension d0. When finished, identify the name and location of your CAD file.

Project Lead The Way, Inc. Copyright 2007 IED – Unit 2 – Lesson 2.3 – Activity 2.3.2 – Parametric Constraints Answer Key– Page 3 Geometric Parametric Dimension Description Value Relationship Equation Overall Plate d0 -- -- 3 in Depth 5:3 ratio; Overall Plate overall plate d1 d0*(5/3) 5 in Width width to overall plate depth 20 times smaller than d2 Plate Thickness d1/20 .25 in the overall width perpendicular Plate Taper to the top and d3 -- 0° Angle bottom plate surfaces ½ the overall d4 Slot Width d0/2 1.5 in plate depth 4/5 of the Slot Width d5 overall plate d1*.8 4 in Location width 1/3 of the Slot Depth d6 overall plate d1/3 1 in Location depth two times the d7 Slot Diameter d2*2 .5 in plate thickness Slot Extruded same as the d8 d2 .25 in Length plate thickness same as the Slot Taper d9 plate taper d3 0° Angle angle Hole Width ¼ of the overall d10 d1*.25 1.25 in Location plate width 2/3 of the Hole Depth d11 overall plate d0*.67 2 in Location depth same as the d12 Hole Diameter d7 .5 in slot diameter Hole Extruded same as the d13 d8 .25 in Length slot height Small Hole Same as the d14 d9 0° Taper Angle slot taper angle

CAD file name and location:

Model the Arbor Press Cover Plate in a 3D CAD solid modeling program. You will need to use geometric constraints to limit the number of parametric dimensions that

Project Lead The Way, Inc. Copyright 2007 IED – Unit 2 – Lesson 2.3 – Activity 2.3.2 – Parametric Constraints Answer Key– Page 4 are needed. Test your results by scaling the object up or down. If all of the parametric equations are written correctly, the object should increase or decrease in size and maintain its geometric proportions. When finished, save the file and identify its name and location in your student folder.

Example Sketch of an Arbor Press Part

CAD file name and location:

Dimension Description d3 Plate Taper Angle d9 Extruded Hole Lengths d10 Hole Taper Angles

Taper Angles and Hole Extrusion Length Dimensions

Geometric Parametric Dimension Description Value Relationship Equation d0 Plate Width -- -- 1 in

Project Lead The Way, Inc. Copyright 2007 IED – Unit 2 – Lesson 2.3 – Activity 2.3.2 – Parametric Constraints Answer Key– Page 5 Twice the d1 Plate Height d0*2 2 in Plate Width 37% of the d2 Plate Depth d0*.37 .37 in Plate Width perpendicular Plate Taper d3 to the front -- 0° Angle plate surface Hole 1 & 4 87.5% of the d4 d0*.875 .875 in width location Plate Width Hole 2 & 3 12.5% of the d5 d0*.125 .125 in width location Plate Width Hole 1 & 2 87.5% larger d6 height than the Plate d0*1.875 1.875 in location Width Hole 3 & 4 Identical to d7 height Hole 2 & 3 d5 .125 in location width location Diameter of 17.2% of the d8 d0*.172 .172 in the holes Plate Width Extrusion Identical to the d9 length of the d2 .37 in Plate Depth holes Identical to the Taper angles d10 Plate Taper d3 0° of the holes Angle Example Cover Plate Parametric Table

Conclusion 1. What is the difference between a numeric and a geometric constraint? A numeric constraint is a location or size dimension that is used on a geometric figure, and can be identified as a numeric value or a parametric equation. A geometric constraint is an assigned relationship that governs the orientation of two sketched elements with respect to each other. Examples of geometric constraints include collinear lines, concentric arcs or circles, parallel lines, perpendicular lines, and fixed points.

2. What advantages are there to using parametric equations instead of numeric values? A parametric equation will maintain a constant geometric relationship between two or more dimensional characteristics of an object. If a dimensional value changes, the parametric equations will automatically change any associated dimensional characteristics, thus maintaining proportionality. Parametric dimensions in a solid CAD model can be linked to spreadsheet programs that are capable of performing more complex mathematical operations. The product of these operations will update the model and all of its associated working drawings.

Project Lead The Way, Inc. Copyright 2007 IED – Unit 2 – Lesson 2.3 – Activity 2.3.2 – Parametric Constraints Answer Key– Page 6 3. What disadvantages are there to using parametric equations for numeric values? Extensive knowledge of the geometric relationships that exist between an object’s features must be understood and identified before the object is generated as a CAD model. This requires a time investment that is not required when using only numeric values. Not all objects experience the types of changes that make the use of parametric equations an efficient alternative.