What condition(s) preclude "Trim" from trimming?

to eliminate the potential for any additional frustration artifacts getting in the way, everything has been redrawn starting with a clean layer. seven OD surfaces were created with “Sweep1”. the seven OD surfaces were converted to closed polysurfaces with “OffsetSrf”. the seven OD polysurfaces were in turn converted into a single confirmed polysurface; a small amount of progress!! see collage below. moving to the first step from the small end of the tube, the axial closure was removed in two pieces using “ExtractSrf” leaving two open edges. using “Iplane”, an infinite plane was created parallel to the first step 1/32" aft from the plane of the step. using “Intersect”, the infinite plane and the OD surface of the smaller tube were intersected to yield a closed intersection curve (ie: an ellipse) to facilitate trimming of only the OD surface of the smaller tube. using “Trim” and the intersection curve as the cutting object, I attempted to trim the polysurface (ie: OD surface of the smaller tube) to NO avail; NO JOY!! what condition(s) preclude “Trim” from trimming??? there’s a valid polysurface with two open edges and a valid cutting object; what am I missing…?


trim problem 1930 013121.3dm (709.0 KB)

what condition(s) preclude “Trim” from trimming??? even thou the basic objective has been accomplished, I’m still interested in understanding why “Trim” didn’t work…


The outer surface of the section you are attempting to trim is connected to the inner surface by two end caps, so you are attempting to trim a solid and not just the outer surface.

As your trim is only intersecting the outer surface the left part of it remains connected via the caps and inner to the right part and therefore cannot be removed. You have to break the loop either by temporarily extracting the surface you want to trim (thereby severing its connection to the end cap); or by creating a second trim ellipse from the surface edge where it joins the cap and, with both ellipses selected, trimming between them; or by deleting the innermost end cap first (if you reckon it to be unnecessary).


thank you very much, that explains totally why I couldn’t trim the end of the smaller tube’s OD surface. I’d only removed the larger tube’s end cap surface. should have seen that; two tubes, two end cap surfaces…