Fancy Holes on Fancy Surfaces (Avatech Tricks Tutorial)

31 May, 2007 By: Fred Washington

Create a helical hole pattern on a conical surface using Autodesk Inventor.

A customer once approached me with a tricky design problem in which he needed to apply a hole pattern to a conical surface. That's not too tricky in and of itself, but these holes had to follow a helical path. He had come up with a method to roughly approximate the pattern, but he wanted a more accurate solution. After testing a few options, the following approach yielded in the best results.

Create a Coil
The first step in making the helical hole pattern is to create the coil feature that defines the location of the holes. Make the profile a line that is aligned with the base of the cone. The output should be a surface. To make sure that the coil aligns correctly with the cone, select the axis of the cone as the axis for the coil on the Coil Shape tab.

Selections used for coil profile and path.

On the Coil Size tab, set the Type information. Choose Pitch and Height and set 11 mm for pitch, 37 mm for height and a taper of -20 degrees to match the taper of the cone.

Values used to generate a coil that matches the taper of the cone.

Completed coil surface feature.

Create a 3D Curve
To create the helical path on the conical surface, you must create a 3D sketch and then use the 3D Intersection Curve tool to generate the path. Selection 1 is the conical surface, and selection 2 is the coil (surface) feature.

Selections for the 3D intersection curve feature.

Create a Set of Work Points
To create a set of work points along the project sketch onto the conical surface, first place one work point at the end of the 3D curve closest to the top of the cone. Next, use the Rectangular Pattern tool to place the multiple points along the 3D curve. Select the original point, select 3D curve for Direction 1, select 18 for the number of occurrences or elements in the pattern, Spacing to specify the spacing between occurrences and select 20mm for the spacing distance.

Selections and settings for the creation of the work point pattern along the 3D curve.

Add Work Axis
To add a work axis on work points and perpendicular to conical surface, select the Work Axis tool, click the right mouse button and enable the Repeat command option. Select the first work point and then the conical face to create a work axis that passes through the work point and is perpendicular to the conical surface. Continue selecting the work points and conical surface until all points have an axis through them. Click the right mouse button, disable the Repeat command option and then right-click and select Done.

Placement of work axis through the work points.

Create Holes
To create the holes using the work points and work axis, select the Hole tool. Then in the Placement section, select On Point, the first work point and the related work axis. Set the depth to 6mm and the diameter to 3mm. Pick Apply to create the first hole.

Placement of holes using work points and work axis.

Continue selecting the work points and work axis until all holes have been created and then turn off the display of all work features.

Completed placement of holes.

Note that because of the geometry, the program can't simply create one hole and pattern the hole along the 3D curve and get the proper orientation for each hole. This situation was also the case with the work axis. However, it's possible that we may see this type of flexibility in future Autodesk Inventor releases.

About the Author: Fred Washington

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