Hi Juan, possibly a better approach for this situation is not to do an actual chamfer, but instead model the piece you wish to remove.

A chamfer has very precise properties, it will follow along the surface contours to the specified distances. In some situations this accuracy actually causes problems, especially since it creates difficult corners where different shaped surfaces come together.

By modeling a cutting edge instead, it is not as precisely defined - the distances of the final created edges from the original surfaces will not be constant like they are in a real chamfer. However, the generated surface will be smoother.

For this different approach, I started by drawing a slanted line like this:



Then I swept that line along the bottom curve that you had. First I made a slight modification to the curve by deleting the points where the side pieces came together, to make those areas completely smooth instead of having a slight crease. That creates this sweep, made of multiple surfaces:



Then I selected all of these surfaces, ran Edit / Trim, and pushed "Done" to cut them all with each other. Then I pushed "Done" again to keep all the pieces, and then deleted the pieces I didn't want to keep. Actually, I deleted just a few of those pieces until I could see and select the 2 long angled pieces, then selected those 2 and the other big pieces, did a Select / Invert and a delete.

After that the pieces can be joined togehter to make a pretty good result:



I have also attached the resulting model here as suela02_chamfered2.zip .

Even though it looks similar, this is not technically an exact chamfer since it is only modeled on the shape of just one curve and doesn't follow the surface at a constant distance by the surface offset. But it has some advantages over a proper chamfer, in that it is nice and smooth in that area along the sides where those surfaces come together, an actual chamfer would be broken up into different pieces right there and then connected by some little faceted corner or something.

Anyway, this may give you another idea on different possible approaches when chamfer doesn't do what you want.

- Michael