Twist Drill

[AndySand]

The solid object I want to draw closely resembles an ordinary twist drill. I find nothing in the archives addressing this question, nor any suggestions in the Vectorworks Help files. I can easily create the cross-section of the object in 2 dimensions, but none of the Extrude or Sweep commands will rotate the object about its centroid along the Z-axis. Placing a 2D or 3D locus at the centroid doesn't help. Nor can I subtract a "spring-shape" coil from a right circular cylinder -- Can't compute... Perhaps I'm working in the wrong solid modeler and someone can set me straight.

[Pat Stanford]

Draw a vertical line. Leave it selected and Create Helix-Spiral. Make it the same radius as your cylinder. Draw a symmetric shape to be the negative of your flutes.

Select the spiral and the shape and Extrude Along Path.

Select the cylinder and the Extrude Along Path and Subtract Solids.

If you need more flutes, then repeat the above at the correct angles (or duplicate and rotate the Extrude before you do the Subtract.

[AndySand]

Pat, the procedure you provided works for a right circular cylinder, which I appreciate your clearing up. However, that was not the problem I'm trying to solve. The shape I want to produce has an asymmetric cross-section. I used the twist drill as a simplified example. Another simple example would be a 1" x 1.5" x 3' iron bar, put it in a vise and twist it. The cross-section is always 1" x 1.5" and rotated around the longitudinal-axis. If I could extrude while rotating, I'd get the shape I seek.

[islandmon]

You can utilize the Loft Tool :

Create Rectangle Profile>ConvertToNURBSCurve>rotate Z=30?>move>Z=6", repeat.

See example:

[Pat Stanford]

If you need it smooth then the Loft as suggested by Islandmon is the correct choice. If you can deal with straight facets and equal distances between steps you could use the Multiple Extrude command.

[AndySand]

You can utilize the Loft Tool :

Create Rectangle Profile>ConvertToNURBSCurve>rotate Z=30?>move>Z=6", repeat.

See example:

Thanks islandmon, this did exactly what I wanted. However, I tried to use the OFFSET Tool to work as advertised to generate the "move". The Help file states "NURBS surfaces are offset by the offset distance along the surface normal direction", which would appear to be an ideal solution. In my VW2008, the tool magnifies the NURB surface profile by the amount of the "offset" in the same working plane as the original. Perhaps I misunderstand the Help description, or maybe I chose the wrong tool.

[Oyvind]

No need for a tool: Use the OIP to set the Z-value.

[AndySand]

To use islandmon's suggested procedure, it's necessary to locate at least three (n) NURBS shapes inline and separated by 1/n the distance of the twist length. Each of the shapes is then rotated by 30? with respect to its neighbor. I found I was using the wrong tool to generate the geometry. The best tool is Duplicate Along Path. It works for very complicated cross-sections.

[Benson Shaw]

If great precision is required, note that the loft kind of stretches a bit between the guide shapes. Create a loft and cut a section between any two of the neighboring guide shapes (section plane parallel to the shapes). The area of the section is not same as area of the guide (My experience, anyway). More rotated guides and smaller rotation = less distortion. This may actually mimic real world stretching when a bar (or a wet towel) is twisted. Apply enough rotations and the bar stretches out to failure.

For the twist drill exercise, Pat's solid subtraction method should result in equal areas for all parallel sections. Stretching in the loft method of twist drill section does not quite map to a cylinder. But both methods are Elegant - thanks for the reminders on these modeling techniques!

-B