Pro/ENGINEER FAQ 2009

This is going to be a challenge, but I’ve got to start somewhere.Geometric tolerancing is a bugger for most people, probably because they get confused by Pro/E’s scope restrictions. That is, you can create your geometric tolerances at different levels: the drawing, the assembly, or the part (selected by the “Model” drop-down in the “Geometric Tolerance” dialogue box)

If you’re just interested in the drawing results, you might choose to create geometric tolerances at that level: Select “The Drawing” in the “Model” drop-down. There are two additional placement options: “Offset” (from a dim, dim arrow, gtol, note, or symbol) and “Make Dim”, which might make things easier. “Draft” gtols could be handy for creating tolerances of straightness, flatness, circularity, and cylindricity, which have no datum references. But, other tolerances, which require datum references, will need draft datums, which will not be parametric. “Draft” gtols do not appear in the model (good or bad?) and undermine the “3-d drawing” idea.

If you’re interested in creating geometric tolerances in your part or assembly, the best working environment is the drawing itself. Creating geometric tolerances in drawing mode is twice as fast as creating GD&T in the part/assembly to show later. The biggest reason for the increased speed is that applying GD&T in drawing mode is more “WSIWYG”. You compose everything in place. No more worrying about attachments and placements, no switching modes.

Creating datum planes, axes, flatness, parallelism, profile, and position tolerances should go pretty quickly. You’ll want to clean up your layer assignments afterwards, but this can be done quite handily in drawing mode as well.

Quite often, you don’t have dimensions to build GD&T with in the assembly. But, you can create cosmetic sketches, datum curves, or surfaces to provide dimensions which can be hidden with layers. This is handy because you can show dimensions for these features and your geometric tolerances will show, too.

One thing that might trip you up: If you have “create_drawing_dims_only“  set to “yes”, you won’t be able to attach a gtol to a drawing dimension.

My recommendations:

1. Just do it.
2. Start with the basics – create the primary datums to support your GD&T scheme.
3. Control the model display by fitting datums to their references, and move all datums from the default axes or planes layer to the gtols layer.
4. Erase datums from drawing views as required with the “Show/Erase” dialog box.
5. Do not use default datums for geometric tolerancing.

PTC Knowledge Base Links:

• Impossible to select a Dimension from an Inheritance Feature to use it as Reference to Place a Geometric Tolerance – merges might have the same problem?