11 Replies Latest reply on Dec 13, 2017 6:49 PM by Dennis Bacon

    Why are these (curved) faces not merging?

    Tyler D.

      Hopefully quick question that I want to sort out now before it comes back to bite me down the road.


      I'm designing this enclosure with concave/convex back/front faces, and it will be injection molded, so I've applied draft to the overall shape prior to shelling.  I added the feature "connector pedestal" to transition into the panel mount flange of a connector, but on the back (concave) face, the two faces have not merged into one.  I can't figure out why not, and if I Measure the edges of a sectioned view it says "the selected items intersect", but it does not list any angle between them or state if they are parallel.



      Any suggestions?


        • Re: Why are these (curved) faces not merging?
          Dennis Bacon

          Not sure why that is Tyler, but if you do a DeleteFace on both surfaces with the Delete and Fill option you do end up with one face.

          • Re: Why are these (curved) faces not merging?
            Richard Gergely

            They aren't 100% tangent hence the initial line. Doing a delete fill has fudged the ting discrepancy.


            If you do a sketch on the original surfaces on the right plane.

            next - intersection curves on the two surfaces


            Analysing these curves gives you the reason

            Angle difference between the two straight lines if fully tangent/collinear would be 180 deg. It is a tiny bit out at 179.9994 deg

            The distance between potential end points with this error  is 0.00004


            In all honesty it's a tiny discrepancy and nothing really to worry about but it's the reason why it left the line.

              • Re: Why are these (curved) faces not merging?
                Dennis Bacon

                I notice that after I answered.. Was trying to think of a good way to explain it. The method I used does fudge it. I extruded that boss in the other direction for a visual and get this.

                  • Re: Why are these (curved) faces not merging?
                    Tyler D.

                    Here's my logic, if it's flawed please let me know, if it's just some machine rounding due to curved surfaces then I'm fine ignoring it:

                    I've got 3deg draft on the sides.  I want the panel mount connector to sit flush on this pedestal which is why I extruded normal to the sketch plane (which gives the image above if extended in the other direction).  But since I wanted a smooth transition in to the rest of the concave face, I put an outward 3deg draft to counter-act the fact that the sketch plane had 3deg inward draft.  Then, since I was adding the 45deg chamfer to the sidewalls other than the concave face, that took care of the unwanted 3deg outward draft.


                    Originally I thought I could extrude along the vertical Y axis, which gives a single face on the concave, and then the 45deg chamfer cleans up the edge anyway, but then the circular section turns into an elliptical section and I thought it may not match my connector nicely.  But in reality that "ellipse" may be so close to a circle that it's no different than 179.9994deg essentially being colinear.

                      • Re: Why are these (curved) faces not merging?
                        Dennis Bacon

                        Ok Tyler,, Take a look at this and see what you think. I created an offset surface of 0 and extended it. Then move both of your original surfaces up slightly. Then did a SurfaceCut. Seems like this for sure would get you what you want.

                        Edit:... Since I'm Screenshot mad.

                        Another Edit:.. Looks like a good way of checking the results of this is to use the "Curvature" tool. My first method of delete and fill shows an inconsistent Rad. of curvature as I move about the surface. I would not use that...  This method of using the surface cut shows the Rad. of curvature (375) consistent throughout.

                        And yes, your logic sounds solid to me but display the curvature on that (your original with the split faces) and you will be surprised at what you see.

                          • Re: Why are these (curved) faces not merging?
                            Tyler D.

                            (Sorry for the late reply, was out of the office for a few days). Thanks for digging in to this more - I was blissfully unaware.  You're right, the results of the display curvature are rather concerning, with weird little anomalies popping up over the surface.


                            I don't use surfaces as much as I should, but am learning that the zero offset surface is a very useful trick to have up my sleeve.


                            The brute force method that I was planning to use before you suggested the DeleteFace method was to just draw the initial extruded boss without the concave surface, then after adding the connector pedestal, performing an ExtrudedCut feature to form the concave face.  I'm assuming this would yield the same result as you got with the surface cut.  Thanks again.


                            [Edit: So I'm not sure if the issue is with the modelling of the geometry or the curvature display tool itself, but it shows me a constant 375mm radius of curvature over the whole surface except the one corner - see screen shot.  On the file you uploaded, this corner shows a radius of curvature of 0, which is itself sort of nonsensical, and when I added these features into my model that I had already progressed on with some other unrelated features, this corner shows a radius of curvature of 10mm.  But such a drastic change from the 375 should be visible.  Going back and trying the Extrude Cut to add the concave surface yields similar result - this time that one corner shows a radius of curvature of 6.7811mm.  I may send a ticket in to SolidWorks as this seems very much like a bug and not something real.]


                    • Re: Why are these (curved) faces not merging?
                      Tom Sidlauskas

                      Reorder the features.

                      Remove the draft from "Connector pedestal"

                      Add a split line for the draft and all seems to work just fine.