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Spline Sketch Entity, Bulge/Buckling Control

Question asked by Jesse Robbers on Feb 10, 2020
Latest reply on Feb 13, 2020 by Andrew Jackson

I could use some help from someone that works with splines often, specifically with splines constrained with many dimensions, and the curvature or 'looks' to be of consumer good quality.


I have a few images attached, simplified drawings of a cell phone, specifically 1 corner of the phone which is replicated 4x's about the phone. The CAD file is 2018, but the sketch and drawing should be easily recreated with minimal effort if using an older version, it's 2 lines + a spline, metric units. Comments within each image helps describe some things.


The drawing is a rectangle, with a spline corner treatment with many dimensions controlling this spline, more than I'm accustomed to working with on a spline, and I'm experiencing some problem that I haven't been able to sort out. Just inside of the 17.77mm dimension the spline is bulging outward beyond the rectangular profile, it shouldn't be.The cut-extrude-1 is not needed, it's just to show material is outside of the rectangular boundary to be cut for visual representation.


One way, the attached file, uses a std. spline with multiple points to match each datum point called out on the drawing for this spline. This spline is also tangent to the straight lines, the handle at each end of the spline set to be vertical/horizontal also as an extra. The handles at the ends of the spline are dimensioned and changing their values didn't resolve this bulge. If I change the handle value for a location further within the spline this bulge area resolves and cut-extrude1 fails, there is no bulged material to cut, but the spline bulges or wrinkles at another place nearer to the spline center. Multiple point splines are messy and not using them is best, not touching all those handles helps, it only gets messy if touched.


Another way, not within the attached model, is I used a style spline with 6 curve degrees. There were points placed and dimensioned to the drawing datum points, the spline had coincident mates to each point, tangency to the lines, end result not good. I tried this with 8 curve degrees, adding collinear mate to the rectangle straight line & the spline end construction handle line(s), end result not good. 


I tried just extruding a rectangle then using a fillet of various types, face fillet, face + hold line, conic rho, curvature, etc..., all of those options. The fillet would match the ref spline sketch at one 1-2 places, but not throughout, end result not good.


In the "X2" CAD file I tried making a boundary surface from edges located 17.77mm from the rectangular corner, to be a surface to cut the corner away from, using different tangency & curvature weighted values, this acted like the fillet. It met the spline corner entity at 1-2plcs, but not throughout, end result not good. I then cut away 1/2 of the corner to make the boundary surface act or be weighted differently and this gets close to the ref drawing spline dimensions, but not exact, and it's curvature gets lumpy throughout the corner. There is a sketch at the end showing the corner doesn't match the drawing.


This is bugging me, I can't sort it out, the model isn't accurate and it should, needs, to be. I'm wondering if someone fluent with this condition could have a look or a go at this to find a good result or to advise where improvements could be made.