Hi Ed, so it looks like another possibility for tubular type shapes is instead of making a circle as the profile that you sweep, make some kind of semi-circle, something like this:



Then sweep that shape instead of sweeping a full circle profile.

The surface/surface intersector seems to be able to deal with this kind of surface at crossing locations much better than with fully closed surfaces crossing each other. But it still should work just as well as far as cutting a groove into your ring goes.

The technique for creating the shape will be to make sure your rail curve is built in segments that have endpoints at the junctures, then when you do the sweep it will build one surface for each of those segments.

See the bottom object in the attached file for how the result of the sweep should be configured with separate surface pieces instead of one long single surface that crosses itself.

Then you need to select 2 pieces at a time and use the Edit > Trim command to slice them with one another and remove the excess inside crossing pieces. Using Trim mode = Keep can be a bit easier for this since it is kind of easier to select the pieces you want to keep rather than the ones you want to throw away. If you see that a trim did not produce a clean looking cut, you may need to select the 2 surfaces and use Construct > Curve > Isect to generate an intersection curve between them and then trim the surfaces with that curve instead. I had to do that in a couple of spots in this case. Anyway when you're done with that trimming you want to have the result like the middle object.

Then you can make that into a solid by drawing in a couple of lines at the ends and using Construct > Planar to make a plane for that end semi-circle piece, then join all those pieces together, then run Construct > Planar to cap off the top, that's how I made the top piece.

Since it is a fair amount of work to do the trimming, you want to only construct one heart section with this method, and then copy that one finished piece over to make the sequence longer. You'll need to make sure the starting curves have a good horizontal end tangent on them so that the pieces will align well.

At any rate, it looks like it would be more feasible to create a tube result using this kind of semi-circle profile shape rather than a full circle tube.

You also might try building things at a bit larger scale, the pieces are getting pretty small in scale in your original size and it is possible to run into some tolerance problems when you've got pretty small sized details. Building this at about 10 times larger scale than your original one may be a good idea.

- Michael