The attached file contains the bottom half of a signet ring. I want to sweep from the side profile through the bottom profile to put some 'flats' on the side of the ring. I cannot seem to get rid of the distortion. Can someone point me in the right direction?

Thank you.

Hi Philip, the main problem causing the weird looking result is that your middle curve is not closed, but the ones on the end are closed curves.

In MoI v2 there is an object type readout that shows the type of the selected object, if you select the middle one it reads here as just "Curve" instead of "Closed crv":



If you zoom in on this area a bit you'll see where it is open:







You'll generally want to have all the profiles have the same kind of closure - either all closed are all open.

When you've got an open curve in there, it means that MoI will only try to flip the curve either one direction or other other and won't be free to manipulate the "seam points" as it normally would to help align things.



But additionally to that, you've also got a configuration here with a differing number of segments between the profiles - the end curves are made up of 2 segments and the middle one is made up of 4 segments. When you have something like that the curves will end up getting kind of averaged together but that's probably not what you want.

Instead you will probably want to use Edit > Separate to break the curves up into pieces, and handle the sweeping in different passes so you can more exactly control how segments will be matched up.

So for example, you'd want to do one sweep with these 3:



Then another sweep with these 3:




Then you would have some planar surfaces to create by the Construct > Planar command and then join the whole thing together.

But you'll need to fix up that gap in the middle profile first.


Whenever you want to have a certain kind of segment matching between different profiles you may need to do the sweep in individual pieces like this - MoI will match up profiles that have the exact same number of segments between them but it isn't able to always understand how you'd like for different patterns to be arranged with differing numbers of segments.

- Michael

Hi Philip, also an different way to model something like that would be like this:

Get a simple surface going first like this:






Now go to the side view and draw in a profile curve that intersects the simple surface, and mirror it to produce this:



Now you can use those curves to slice up the original surface, select the ring, run Construct > Boolean > Diff, and select those 2 curves the cutting objects. That will slice up the ring and leave these pieces behind:



Delete the pieces you don't want:




You may find it easier to try different shapes quickly by being able to draw in the profiles of the cuts like this, and then this lets you focus on just producing a more simplified surface with the initial sweep.

- Michael

Dear Michael,

Thank you very much for your reply. The separate sweeps are giving me almost exactly what I need but I cannot create the planar surfaces. If you have a moment to look at the attached I would be most grateful.

Thank you.

Philip

Hi Phililp, the sides you have there did not end up being planar, if you switch to the Right side view you can see:



Notice how the profile is kind of curved and shrinks inwards near the bottom?

It looks like your middle profile curve is not quite as wide as the others, so it does not end up tracing out a planar shape along the sides.


So instead of Construct > Planar for those particular areas you will need to use some other technique, like for example select these 2 edges and then run Construct > Loft :



Or you could also use sweep with those 2 edges as the rails and the little line as the profile curve, or you can use the other technique I showed above where you would cut in those side pieces with booleans instead.

- Michael

Michael,

Many thanks for all that information - problem solved and a few other subtleties that I hadn't appreciated highlighted too.

Regards,

Philip

Hi Philip,

Another option I sometime use when having to do a half shank like your example is to make the 3 profiles identical at the start.
Then with the middle Profile you can Scale 1D to adjust its height or switch on Points & move them to suit your needs.
Because all the Profiles have been made the same way, they'll then Sweep correctly.

HTH, Colin

Hi Philip,

I often use Colin's method when building the lower part of the shank on a signet ring.
Having the same number of control points in the profile curves helps to steer the sweep in the right direction.

I took another approach to build a shank that still has the flats on the sides at the base, but without the sharp creases.

I filleted 2 corners on the bottom profile curve just a little and then drew an arc
on the outer side of the shank. Then all the curves were used for a network surface.
I did a 0.2 mm fillet, but you may want to use a smaller fillet..it will still work.

When modeling a signet ring in two halves such as this, the lower shank must blend well into the top of the ring, so that must be considered
when drawing the outer arc. You can sometimes use the "cont" arc to make a good transition between the top of the ring and the shank
Hope this makes sense.

Jesse

In Michaels method, where he cuts the sides of the ring off, if you be carefull to keep the seam edge out of the cut, I like to use the "Blend" tool to create the "fillet". Just delete the flat face. Can almost make a variable fillet.