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Weird edge in the middle of smooth loft.
MDesign
Member Posts: 748 ✭✭✭
So I was looking for a nice butt plate to use as a template and couldn't find any that that used complex surfacing like I needed so I did my own. What can cause this weird "edge" in the middle of a loft like this? both profile sketches are tangent.where that edge passes thru. the vertical center-line is a bezier curve and the horizontal one is two arcs that are tangent. Not really an issue for this project but was curious why that happens?
Best Answer
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S1mon
Member Posts: 3,296 PRO
You would be much better off building this as a gently curving surface which has mirrored control points for the cross-curves, and an almost vertical surface and then make a blend surface (pseudo fillet) between the two at the end. Three-sided lofts are nasty, especially when you're asking Parasolid to approximate a spline/arc/spline with a multi-span degree 3 curve. Then you're lofting to the mid-plane curve which has a very different structure. The curvature plots are very spiky where you see the shading issues. Loft doesn't usually produce the best surfaces. It's willing to do a lot of things, but creating great surfaces isn't always its forte.
Looking at your sketch 1 and sketch 2, I would recommend reviewing the "golden rules" for Alias. The underlying math is basically the same for surfaces in Onshape.
https://help.autodesk.com/view/ALIAS/2024/ENU/?guid=GUID-A23E9E8C-6D6B-41AD-A0AB-3E98183FBC2E
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Answers
Maybe they're tangent but very curvy at that edge? Share the doc?
added link to sample
You would be much better off building this as a gently curving surface which has mirrored control points for the cross-curves, and an almost vertical surface and then make a blend surface (pseudo fillet) between the two at the end. Three-sided lofts are nasty, especially when you're asking Parasolid to approximate a spline/arc/spline with a multi-span degree 3 curve. Then you're lofting to the mid-plane curve which has a very different structure. The curvature plots are very spiky where you see the shading issues. Loft doesn't usually produce the best surfaces. It's willing to do a lot of things, but creating great surfaces isn't always its forte.
Looking at your sketch 1 and sketch 2, I would recommend reviewing the "golden rules" for Alias. The underlying math is basically the same for surfaces in Onshape.
https://help.autodesk.com/view/ALIAS/2024/ENU/?guid=GUID-A23E9E8C-6D6B-41AD-A0AB-3E98183FBC2E
@S1mon
Didn't quite do it the way you suggested. Ended up building it with just surface loft of half of it using sketch 1 and 2 curves. with the section profiles as guides with much better results. just had to fill in the underside half with a fill surface and mirror and got an acceptable result. Thanks for the info on Alias rules. Will be my guiding light going forward. No expert at curve combs but this is definately less jaggy.