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Pro/Engineer   April 2004   Tip-of-the-Month

Dimensioning Schemes for Saved Sketcher Sections

A fast way to repeat features of similar geometry in different models is to save sketches of often repeated sections.  How many times have you sketched the same basic geometry over and over?

Sketcher Section
Figure 1.  Sketch with dims to References
Placed Section
Figure 1A.  Placement of saved sketch
     from Figure 1

Figure 1 is a simple example of a section that may be used in a number of ways -- perhaps as a slot or a raised pad.  Saving the section makes it easy to drop into any new feature to be sized as needed.

Saving the section is easy -- simply use File > Save in Sketcher when the section is complete.

Using the section again in another feature is also easy -- Sketch > Data from File > Browse to the section and place it.  Options include Scale and Rotate fields in the placement dialog.  (See January 2003 Tip-of-the-Month for additional information.)

Making the sketch easier to reuse is this Months Tip.

When saving a sketch, there are a few things to remember:

  1. The saved sketch includes only the sketched geometry, not references.
  2. Not all constraints will be saved.  Strong constraints have a better chance, but reconstraining may be needed after placement.
  3. Dimensions between sketched entities will be saved, but not dimensions to references.
  4. Geometry created from Use Edge or Offset Edge can cause problems.  Avoid them.
  5. The saved sketch can be scaled and rotated when it is placed.

Sketcher Section
Figure 2.  Sketch with dims to centerline
     entities over References

Placed Section
Figure 2A.  Placement of saved sketch
     of Figure 2

The key to making a sketch that easily saves and places is to have the dimensioning scheme well defined.  For example, the section of Figure 1 will copy without the 2 location dims (2.0 and 2.2) as shown in Figure 1A.  By sketching construction lines over the references, then dimensioning to the construction lines (use Query if unsure) instead of the references (as shown in Figure 2), the section will save the placement dimensions and scheme.

The added construction lines of Figure 2 will also make the section easier to place because it has lines corresponding to the references.  Figures 1A and 2A show how the respective sections will look by default when they are placed as new sections.  Note the dimensioning and constraints.

After placement, look at the constraints to be sure they are appropriate.  Sometimes the constraints are not as you would expect -- especially tangent constraints with splines and conics.  Often there is a 180 degree dim (Figure 3) instead.  Sometimes you cannot re-make the tangent constraint so it has to stay dimensioned as 180 degrees.

(I do not understand why some constraints are saved and some are not -- especially tangent constraints for splines and conics.  See Figure 3.  This is a good place for PTC to do little more work.)

Some things to do when saving and placing a sketch:

  1. Explicitly sketch all geometry to be saved.
  2. Make desired constraints and dimensions strong.
  3. Place sketched entities at references (construction lines, points, etc. at references are good).
  4. Dimension to sketched entities not references.
  5. Think about how the section will be placed later and make the dimensioning scheme fit the expected reuse.
  6. After saving, move the section file to a sketch directory and rename it.  See the TIP below.
  7. At placement use the Scale and Rotate fields in the placement dialog to set the section, then modify dimensions as needed.
  8. At placement double check the constraints to be sure they are correct.

Sketcher Section
Figure 3.  Failed Tangent Constraint
TIP - When saving a sketch, use the default name.  Pro/E has some funniness about naming.  Just use the default (something like s2d0012.sec), then rename the file and move it to your section library with whatever file manager you like.  Renaming to something meaningful and moving it to a Sketch directory will make it easy to find later.

Have fun saving time and speeding up your work!


See You Next Month!
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