Tip #1. Drafting a boss using a revolved protrusion. Draft on boss fails because of tangency lines. Situation: You are creating a simple neutral curve draft on a screw boss in your housing and Pro/ENGINEER comes back with the failure window. This is because Pro/ENGINEER can sometimes have difficulty calculating geometry that crosses over tangency lines. Solution: Create a revolved protrusion to add the draft geometry. Set up the section plane to go through the axis of the boss. The height of the protrusion should intersect the adjacent wall but not go through it completely.

Boss is drafted using the revolved protrusion method.		Sketching the revolved protrusion.

Tip #2. Drafting a boss using a revolved surface.

Unintended geometry from the revolved protrusion.

Solution: By using some basic surfaces that are now offered in the Pro/ENGINEER® foundation package, you can add the draft correctly and avoid the unintended geometry.

1. Create a revolved surface to add the draft geometry. The sketch should be similar to the one used in the previous tip.		Creating a revolved surface.
2. Copy the surrounding boss surfaces using a surface copy.		Copy all core side surfaces that intersect the revolved surface.
3. Trim the revolved surface using the surface copy.		Trimming the revolved surface.
4. Patch the surface on to the boss or use a protrusion from quilt.		Turn the surface into a solid.

FYI

Although Tips 1 and 2 both use revolved features, it is also possible to use a sweep or variable section sweep (pivot dir) to create the geometry. This can be especially effective when drafting ribs that cannot be simply drafted using the Draft command. When using the variable section sweep (pivot dir) to create your draft, be sure to pick a pivot direction plane that is normal to the part ejection or side action. A variable section sweep with a “pivot direction” should be used instead of a “normal to trajectory” to ensure that the draft angle being swept around remains constant.