Tips on Editing Spline Curves with ZWCAD

By Carol Miller, a participant of ZWCAD Design Contest 2010

At the beginning of 2010, an article in a newsletter caught my eye. It was about the ZWCAD Design Contest 2010, and the topic for the contest was on designing the future. Winners would receive an iPod Touch or iPod Nano music player, and a license of the new ZWCAD 2010 software. The way I saw it, any unrestrained creativity is a futuristic style – all I needed to do was to exert my imagination to the greatest extent possible.

I drew a high-heeled shoes car, and to do this, the spline is the best tool for creating smooth curves. In addition, spline editing with the SplinEdit command makes the smooth curves even more perfect. As I created drawings for the contest with ZWCAD, I found some techniques that I would like to pass along to you as tips.

ZWCAD 2010 enhances spline editing with more options. Let me share with you a couple of tips and tricks in using SplinEdit.

Tip 1: Adding Points to Broken Splines

The shape of spline is defined by fit points and control points. When you select a spline, grips are displayed at the fit points; after certain operations, however, fit points are discarded and grips are instead displayed on control points. Moving the grip changes the shape of spline, of course, and more points means smoother splines.

Adding fit points is easy: just enter the SplinEdit command, and then enter F to choose the Fit Data option. However, after other editing operations, such as break and trim, the Fit Data option disappears; the spline no longer includes fit data. So how can you add points to a broken spline? Here is a tip that uses the Refine option. Follow these steps:

Command: splinedit
Prompt: Fit Data/Close spline/Move Vertex/Refine/rEverse/Undo/: (Type R, and then press Enter.)
Prompt: Enter a refine option [Add control point/Elevate order/Weight/eXit]/: (Type A, and then press Enter.)
Prompt: Specify a point on the spline : (With the mouse, pick a point on the spline.)

In this way, a control point is added to the spline.

Tip 2: How to Convert Splines to Polylines

Splines create nice smooth shapes, but CAM (computer-aided machining) programs cannot read splines – what a pity! A solution is to convert the splines to polylines using Flatten command. (Flatten is not the only solution; alternatively, you could save the file in R12 DXF format. Since the R12 format does not support splines, ZWCAD converts them to polylines automatically. The drawback is that such old file format can erase certain types of newer entities. For this reason, it is best to use the Flatten command.)