Learn CAD with SolidWorks 2008 - Sketch entities overview (C) –ellipse, partial ellipse, parabola, spline creation - by John Sinitsky

Categories : Cad and auto cad
Tags : Mechanical engineering

Introduction

SolidWorks2008 is a popular CAD tool, that is used by millions all around the world. The SW approach to 3D modeling is based on creating sketches and applying certain operations on them, creating “Features”. To ease the sketch creation, sketch entities were introduced.

Sketch Entities

As it was mentioned in previous articles once you enter the sketch, beside the “Exit Sketch” and “Smart Dimensions” buttons, you will see several predefined sketch entities.Those entities are:

Line
Rectangle
Polygon
Circle
Arc
Sketch fillet/chamfer
Spline
Ellipse
Point
Text

Each entity has several options that appear in the place of feature tree once you have selected you choice – as described below. The line, circle and rectangle were cover in “Sketch entities overview – part I” and arcs, points and polygons were discussed in “Part II”. Now we move on to more advanced options.

Ellipse, Partial Ellipse and Parabola are all combined under “Ellipse” sketch entity. This is new feature in SolidWorks 2008. However, those cannot be switched once you have selected one – they are actually different features.

Ellipse

Ellipse is defined by 3 clicks. The first click defines the center of the circle that you will eventually “shrink” to ellipse. The second point will define this “construction” circle radius – becoming the primary ellipse radius. After clicking twice and before the third click you will see the ellipse contour changing according to your mouse position. This wil conclude the ellipse construction by defining ellipse’s secondary radius.

Partial ellipse

Constructing partial ellipse is very ellipse definition process. However, once you have clicked for the second time, your third click will not only define ellipse secondary radius, but also serve as start point for your partial ellipse creation. The forth click will conclude the definition, with ellipse’s “second center” point created as well.

Parabola

The parabola is defined by 4 points.

Parabola center/origin – the point that defined parabola “symmetry”

parabola midpoint – the point on the parabola line from which the 2 “half-curves” of the parabola will originate

Half-curves ends - 2 points defining the “half-curves” lengths

Spline

The spline is a curve which can be defined by its points and curvstury in points proximity. When constructing a spline you will see the first line being straihgt line and afterwards you curve for will change with each point added. To finish constructing an open-ended spline click the mouse twice for the last spline point. After the spline is created, it can be edited by changing the line curvature by “playing” with the arrows that are related to each spline point. You can also show the spline curvature graphically to have a better control over your spline.

Summary

This concludes the overview of main sketch entities, used for construction. They can be also combined, trimmed, extended and much more to give you an increased control of sketch creation process.

This post is part of the series: CAD modelling with SolidWorks 2008

Are you a CAD user? An engineer? Product designer? What software do you use? Try SolidWorks - and you may never want to switch back… Already a SW user? This series will give you some useful tips about the latest version, SolidWorks 2008.