Monday

Everybody can Draw Springs Without the Helix Command

5 Comments Jan-12-2009 | Posted by Gültekin Özkan | Printable Version | Level |

Hi there,

It is undoubtedly easier to create solid models with software like Inventor, Solidworks, IDS and Catia. They either have dedicated commands or allow you to ‘sweep’ along 3D spirals. Whereas in AutoCAD this process can be quite problematic as sweeping is not allowed with 3D paths. (except in 2007+ versions..).

So what happens when you can’t sweep with 3D curves? You use some Turkish-sense here- find a practical solution!.. Let’s begin:

Fig.1 We’ll start off with a semi-circle.

We’ll begin by defining the path (axis) of the spring. Dimensions? Take R= 25 mm. So we now have half a circle (arc) 25 mm in raduis.

Fig.2 MIRROR the ARC to get a symmetric COPY.

MIRROR the ARC to get a duplicate of it. It looks like a complete CIRCLE from afar. We need to define the angle of inclnation to determine the step intervals. Imagine that you know the intervals in terms of distance, and then calculate the angle necessary using trigonometric knowledge. Say we need 15 degrees. That’s 7.5 (seven point five) degrees in each half.

Done with the calculations now construct the spring. Switch to an isometric view.

Fig.3 Switch to an Isometric view.

We will rotate the arcs on different directions keeping them in touch, that is, about one of their touching points. Because the UCS is set at TOP view, switch to LEFT view and then Isometric view to set the UCS to fit our use.

Figure.4 View from the left side…

Pay attention to the UCS. We’re looking at the drawing from the left. Keep in mind that in AutoCAD, you’ll alwaysbe working on x-y plane. What we actually did was to bring the x-y plane to the left view. Now it time to rotate the arcs..

Seperate the ARCs. Then draw a circle that represents the cross sections (r=4mm). Now rotate both the arcs and the circles 7.5 degrees in opposite directions. Pivot points should be the center points ofthe little circles.

Figure.5 7.5 degree rotation in opposite directions…

The ROTATE command will ask you to firstly select the objects (the arc and the circle) you wish to rotate and then the base point (center of the circle). After these selections, you’ll be prompted for the amount of rotation (7.5 degrees). You should now see something that looks like this:

Figure.6. These curves will help form the spring.

Now repeat the same process for the other half, (-7.5 degrees rotation..). now you have your crooked-looking half circles looking at each other.

Solid modelling time!

Activate the EXTRUDE command. When prompted to specify the cross section, reply by selecting the little circle. Now type ‘P’ (keyboard shortcut for PATH, meaning that we want to define a path that the little circle will be extruded through..) and select the arc. It worked didn’t it? It should work under normal conditions if nothing is wrong with you or your computer.

Figure.7 Easy to do once you’e got the path ready.

From the SHADE menu, select “gouraud shaded”, let’s have a better look at it. Remember that we worked keeping the left side of the ARCs? Yes, now join them from the center points of their left ends. Use the Union command to form them into a single solid.

Figure.8 Join and then ‘unite’ the halves using the UNION command.

Now its time to add as many rounds as you need to form a continous spring. Copy as you wish, and don’t forget to UNION them!