Asee peer logo

Investigating and Comparing Two Different CAD Methodologies to Create Top-down Assemblies

Download Paper |


2016 ASEE Annual Conference & Exposition


New Orleans, Louisiana

Publication Date

June 26, 2016

Start Date

June 26, 2016

End Date

June 29, 2016





Conference Session

CAD Within Engineering Design Graphics

Tagged Division

Engineering Design Graphics

Page Count




Permanent URL

Download Count


Request a correction

Paper Authors


Ibrahim F. Zeid Northeastern University

visit author page

Ibrahim Zaid is a professor of mechanical, industrial, and manufacturing engineering at Northeastern University. He received his Ph.D. degree from the University of Akron. Zeid has an international background. He received his B.S. (with highest honor) and M.S. from Cairo University in Egypt. He has received various honors and awards both in Egypt and the United States. He is the recipient of both the Northeastern Excellence in Teaching Award and the SAE Ralph R. Teetor National Educational Award.

visit author page

Download Paper |


There are two main approaches to create CAD assemblies using commercial CAD/CAM systems: bottom-up or top-down. The bottom-up approach is more intuitive and therefore more commonly used. This is the traditional approach. We follow three steps to create assemblies using the bottom-up approach: (1) create the parts, (2) insert them into an assembly model, and (3) use mates to assemble the parts. The top-down approach is also known as in-context approach. It is preferred for conceptual design when a design team is trying to conceive a new product and the layout of its components relative to each other in the assembly. It is a first step to define the design intent of the product (assembly) being designed. The top-down approach is also more efficient to use than the bottom-up for large and complicated assemblies because it reduces errors within the assembly. The top-down approach uses a layout sketch (also known as a skeleton or napkin sketch) to relate the assembly parts together. Some view the layout sketch as a way to claim space for the components in the assembly because it shows how the components are laid relative to each other. Others view it as a block diagram or a reference sketch of the assembly, establishing relationships and parameters for the parts of the assembly and their dimensions to facilitate their automatic placement in the assembly.

One of the problems with top-down assembly approach is to find the best method to create the assembly. There are two methods to create top-down assemblies: layout sketch, master model. These methods technical comparisons and evaluations are not available. The layout sketch is where the designer sketches the skeleton of the parts. The main goal of the layout sketch is just that: a sketch to show both the assembly layout and the main dimensions of the assembly. Use the layout sketch to define the component size, shape, and location within the assembly; make sure that each component references the geometry in the layout sketch. We cannot create more than one layout sketch in the assembly. The master model uses two ideas: split model, and create separate bodies.

We design three examples of assemblies: basic, medium and advanced. We use SolidWorks CAD/CAM system to create each assembly using each of the top-down assembly approaches.

We have completed the creation of the first basic assembly. The results indicate that the layout sketch technique is more efficient than the master model technique. We will perform the other two assemblies to extend our investigation. We expect the master model approach to be better for more complex assemblies. We will provide an analysis metric of the different approaches.

Zeid, I. F. (2016, June), Investigating and Comparing Two Different CAD Methodologies to Create Top-down Assemblies Paper presented at 2016 ASEE Annual Conference & Exposition, New Orleans, Louisiana. 10.18260/p.25471

ASEE holds the copyright on this document. It may be read by the public free of charge. Authors may archive their work on personal websites or in institutional repositories with the following citation: © 2016 American Society for Engineering Education. Other scholars may excerpt or quote from these materials with the same citation. When excerpting or quoting from Conference Proceedings, authors should, in addition to noting the ASEE copyright, list all the original authors and their institutions and name the host city of the conference. - Last updated April 1, 2015