Helical Sweep

Springs and screw threads are the classic examples of using a Helical Sweep, but think about how you might produce a knurl pattern using this functionality.  Think of this feature as a constant section sweep along a helical path.

 

 

 

 

Required Attributes

Axis – cylindrical centre of the form

Pitch – the distance travelled along the axis for each 360 degree revolution of the helix

Profile – like a Revolve, the cross section of the cylindrical form

 

Section Orientation

References tab > Through axis of revolution  or  Normal to trajectory

This defines whether the section sketch plane remains vertical (parallel to or through the axis – default setting) – or if it is normal to the sweep trajectory – the helix.

The effect of this choice can be best seen in a sweep with a ‘fast’ helix – a pitch greater than the profile length.  In the image (above left) you can see the sweep section is distorted if the option Through Axis of Revolution is used – the sketch plane is at an acute angle to the trajectory.

The feature in the right of the image looks more like a standard sweep – the sketch plane is always Normal to the trajectory.

 

Right or Left Handed

Simply the direction of the helix.  A standard screw thread is right handed.

 

Pitch

This is the distance the helical ‘spiral’ moves along the axis for each 360 degree turn.  Input a figure in the prompt in the text area of the screen and hit the tick.

You will then enter a 2nd sketch environment to create the cross section of the sweep

 

Section

Make sure you identify which reference is the axis and which is the outer profile as its an easy mistake to draw the section up against the axis!

 

Variable pitch

Select Variable rather than Constant pitch [second feature in top image above]

The Profile can still be any shape.

A single line will allow a start and end pitch with a smooth transition from one to the other over the length of the sweep.

If you want the pitch to be different values at various points along the profile then you need to break the profile into sections at the points you want the pitch to vary.

You will be prompted for the start and end pitch.

A graph will then appear which shows the pitch along the profile.  Pick the break point on the profile sketch to add them to the graph and define a pitch at that point.

If you want to change the values, use the Change Value option in the Pitch > Define Graph menu.

 

Vary section

Options tab > Vary Section

Creates a sweep with a variable section. Uses section relations with the Trajpar parameter to vary dimension parameters in the sketch.

Non cylindrical helixes – see Trajpar in Mathmatical control