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Pro/Engineer   July 2001   Tip-of-the-Month

Tricks to Making Patterns

When creating a pattern, especially a rotational pattern in Pro/E, there are some pitfalls to watch out for.  Here are some tips that can help.

Choose the Correct Pattern Options:

Pro/E gives 3 options for creating patterns, Identical, Varying and General.

  • Use Identical if all instances are the same size and placed on the same surface. Identical patterns are the simplest and regenerate the fastest of the three options.  For an Identical pattern, the system generates the first feature, then copies it exactly, including all the intersections.
  • Use Varying if the instances vary in size or may be placed on, or intersect different surfaces.  For Varying patterns, Pro/ENGINEER generates geometry for each feature individually, then generates all the intersections at one time.  Since intersections are created as a whole group, DO NOT use Varying with Thru Next.
  • Always use General if a patterned instance might touch (intersect) another instance, intersect itself, or cross surface boundaries or edges.  The system makes no assumptions about the instances of General patterns.  Therefore, Pro/ENGINEER calculates the geometry of each individual instance and intersects each feature separately.  This option takes the most regeneration time, but is typically the most robust.
It is best to evaluate the geometry and consider how the part may be changed and pick the best option.  It is possible (most times) to redefine pattern options if the geometry has changed, causing the feature to fail.

Rotational Patterns:

Rotational patterns are created by using an angular dimension as the pattern parameter.  For best results, this angular dimension should position a datum plane created on-the-fly.  (See June 2001 Tip.)  This datum can be the sketching plane or a horizontal/vertical reference created in the lead feature before the pattern is created.  The feature to be patterned must not reference any geometry, features, locations, or intersections that will change as the feature is rotated.  Care must be taken in the sketch to ensure only the desired elements are referenced.

Pattern Element Sketch A Trick to minimizing references for a rotational pattern is to reference only the center axis (from the part, at the center of the to-be-created pattern) in the sketch, then draw horizontal and vertical centerlines through the axis point.  The centerlines become the dimensioning source.  See the image.  In this way there is only one reference for the sketch.

If you place a rotational pattern on a revolved surface, always choose Varying or General.  This is necessary because revolved surfaces are divided into two halves.

Ref Patterns:

Ref patterns are a great way to pattern multiple features.  A reference pattern creates patterns a feature "on top of" any other patterned feature.  The feature that is to be included in a Ref Pattern must:

  • Reference only stable global references that will always be consistent for each pattern member -- like a center axis
  • Reference at least one element created by the original pattern.
Tip:  It is a good idea to reference only 1 feature of the original pattern when possible.  Sometimes Pro/E gets confused if more references are made.
  • Do not reference more than one pattern -- Even if a second pattern references a first, make references to features of only 1 previous pattern.
  • It is very important to create the new feature on the leader of the original pattern.  Use the Model Tree or look at the axis numbers (if applicable) to determine the leader of the pattern.
With a Ref Pattern, the pattern options (Varying, General) and their associated characteristics are taken from the original pattern.  If they need to be modified, it must be done in the original pattern.

Other related tips from our Tip-of-the-Month Library include patterning tricks for Patterns of Patterns and Converting a 2D Pattern into a Non-Uniform Pattern.

One item missing from patterns in Pro/E is the ability to reroute or redefine the references and/or parameters chosen for the pattern.  Right now if you wish to make these changes, you must delete the pattern and re-create it.  If enough of us request a change to this, maybe PTC will include it in a future release.

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