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Session 3538

Dimensioning through understanding geometry Niaz Latif, Doug Graham Northern Kentucky University / Holy Cross High School

Abstract

Dimensioning practices and standards are usually taught in introductory courses in Engineering Graphics. Knowledge of these practices is valuable to graphics students. It is also essential that students learn to dimension a drawing completely so it will describe its geometry and avoid missing dimensions. A teaching method to instruct dimensioning practices in Engineering Graphics is discussed in this paper. The "Simple Geometry Method (SGM)" involves an understanding of a drawing by process of simplification. A drawing (complex geometry) is created from several simple geometries such as lines and circles. Therefore, it is important that students identify these simple geometries and provide dimensions for them. By following the SGM students will notice all required dimensions to describe the complex geometry. Preliminary data analysis showed that SGM significantly improved the students understanding and learning of dimensioning practices to avoid missing dimensions.

I. Introduction

Students in introductory graphics courses typically study the standard practices of dimensioning that includes types of dimensioning; current standards; symbology; units and etc. Although these factors are important, the value of complete dimensioning in order to describe the geometry of an object is often undermined. By failing to understand this, dimensioning by students results in missing dimensions. A complex geometry is created from several simple geometries. If students can recognize these simple geometries and can provide dimensions for them, they will not miss any required dimensions.

The objective of this paper is to: 1) introduce a teaching method to avoid missing dimensions in a drawing, and 2) present results from classroom trials of this teaching method. Classroom trials were performed to insure the validity of this approach. Two institutions, a four-year college and a high school, took part in the study. The studies involved pre-tests and post-tests to evaluate students performances before and after learning SGM.

II. Method

Nearly all geometric shapes, such as arcs, polygons, ellipses can be described in terms of lines and circles (Figure 1a. and Figure 1b.). Therefore, a complex geometry can be identified as the combination of several simple geometric shapes1. Lines and circles are the best to illustrate a complex geometry. Once students recognize the composition of geometry in terms of lines and circles, they only need to provide the dimensions of these. Also, students will recognize types of circles (concentric, eccentric, etc) and types of lines (intersecting, tangent,

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Graham, D., & Latif, N. (1999, June), Dimensioning Through Understanding Geometry Paper presented at 1999 Annual Conference, Charlotte, North Carolina. 10.18260/1-2--7590