Profiles must follow these rules:

• You must sketch a centerline to define the axis of revolution.
• The sketched entities must be a single string of connected segments
• The string must not cross over the centerline
• The string must never go normal (perpendicular) to the centerline (i.e. can't loop back)
  
• If you chose Norm To Traj, the profile entities must be tangent to each other (C1 continuous).

Exercise: CONSTANT PITCH SPRING

1. Start a new part file with default datum planes, and name it [Spring].
   
2. Choose Feature > Create > Solid > Protrusion > Advanced > Done, then Helical Swp > Done. The system displays the feature creation dialog box.
   
3. Review the choices available in the ATTRIBUTES menu, then Done to accept the defaults. (Constant, Thru Axis, Right Handed)
   
4. Select a sketching plane that represents the spring's vertical side view with an appropriate horizontal reference.
5. Choose or Accept the Sketching Reference planes.
   
6. Select Centerline and place it vertically on your vertical reference datum plane to represent the axis of revolution.
7. Sketch a tangent chain of entities, as shown below, to representing the profile of the surface of revolution.
8. Dimension and Regenerate the Profile of Revolution as shown below.
   
9. When you have finished sketching the profile section, choose Done.
   
10. Enter a pitch value of [0.12] (the distance from one coil to the next)
    
11. Pro/ENGINEER places you in Sketcher mode to sketch the cross-section that will be swept along the trajectory.
    
12. Sketch the cross-section based about the visible cross hairs per the diagram below. Dimension and regenerate the cross-section.
    
13. Choose Done.

VARIABLE PITCH HELICAL SWEEPS

Helical swept features can also be created with a variable pitch. In this case, the distance between the coils is controlled by a pitch graph.

The initial graph is created when you specify the pitch value at the start and end points. You can then add more control points to define a complex curve that governs the distance between the coils along the axis of revolution.

The following options are available in the DEFINE GRAPH menu:

• The Graph is only for displaying the pitch data assigned to the Profile curve.
  You cannot select anything from the Graph directly.
• Add Point - Add a reference point to the graph by selecting a point in the profile section, or the start or end point. Enter the desired pitch value at this point. The system locates the selected control point along the X-axis of the graph and draws a line with the length equal to the specified pitch value.
• Remove Point-Remove a pitch control point by picking it in the profile section.
• Change Point-Change the value of the pitch at any selected control point, including the start or end point. Select a point in the profile section to change its value and enter the new value.
  

Exercise: VARIABLE PITCH SPRING

1. Start a new part file with default datum planes, and name it [Spring-variable].
2. Choose Feature > Create > Solid > Protrusion > Advanced > Done, then Helical Swp > Done. The system displays the feature creation dialog box.
3. Define the feature by selecting Variable, Thru Axis, Right Handed from the ATTRIBUTES menu, then Done.
4. Select a sketching plane that represents the spring's vertical side view with an appropriate horizontal reference.
5. Accept the Sketching Reference planes. (Close)
6. Select Centerline and place it vertically on your vertical reference datum plane to represent the axis of revolution.
7. Sketch a single line, as shown here, to represent the profile of the surface of revolution.
8. Sketch two Points on the line and dimension them as shown. Then Done.
   They will be used as the control points in the pitch graph. These control points define how the pitch value changes along the axis of revolution.
   To sketch points, choose Sketch > Point, then select points on the profile geometry and dimension them.
   Note: You may put them on the centerline that defines the axis of revolution if you desire.
9. When prompted for the Pitch value at the start and end of the trajectory, enter [0.10].

10. While the profile section is displayed in the original window, the system displays a subwindow with the initial pitch graph in it. Note: The graph window is for display only, so you can move it to the lower right corner of your window.
11. Choose Define and Add Point from the GRAPH menu.
12. Pick in the main sketcher window on the one of the additional sketched points that you added to the helical profile curve and enter [0.200] for the pitch value. Then add the other point giving it the same pitch value.
13. Your graph should look something like this one:
    (Note: some of the connecting curves may not show due to a software issue)
14. Once the graph is defined, choose Done from the DEFINE GRAPH menu.
15. You are placed in Sketcher mode again to sketch the cross-section that will be swept along the trajectory. Sketch, Dimension, and Regenerate the section. Then Done
16. When you have finished, choose Preview.
17. Now redefine the Pitch graph by selecting Pitch then Define from the Protrusion dialog box. Do a Change Value of the both the end points, and set the pitch to [.005] (approximately zero). Done, Preview and/or OK.
18. The resulting feature is shown in the following figure.