I’m following up on suggestions by Jim and trying some trim operations. Is there a command to fill an opening left by such an operation. I’ve used CAP to fill open extrusions.
e.g. I uses a cube to trim part of a solid cube. this is what I have left. Must I draw/create faces to fill the openings, or is there a command?
in such a case you should use boolean difference it will not create such an open part. in case that still happens and/or you somehow need exactly this method, you can still extrude the lower curve of that opening and join it all together.
Now you get to arm wrestle with jim!
-Pascal
I had an earlier post where I was having problems with Boolean difference. Forum Member Jim suggested trimming. I have not used that command in this method so I’m experimenting. I’m just wondering if there is a command similar to Cap for situations like this.
No. Cap is limited to Planar holes so there is a single solution.
6 nonplanar edge curves could imply a variety of different surface shapes.
In this case you could Loft or Rail Sweep two opposing surface edges to make one surface, Join it to the others, then use Cap to close the remaining planar hole.
Rhino is a “Surface” modeler so you need to think about your modeling in terms of surfaces.
yes Jim is very notorious around here for persistently trying to convert everybody into a boolean hater 
he has a point though but ignoring booelans completely is also not the right method.
one way to gap this would be to use FillMeshHole(s) which of course only works if you mesh it first so probably not much of an option. rather use extrude as i suggested.
I found EdgeSrf. This seems to have done what I needed.
Sure, that will work.
I’ll experiment with FillMesh. My final output is stl, so a little experience working with meshes helps.
The point with the trim workflow is that you have all the surfaces that you need. So you don’t need geometry creation commands to fill the holes in one object that were created by trimming that object with the surfaces of another object. You just trim the other object with what is left of the surfaces of the first object. Then join.
Its good to see there is somebody left who has not clouded their thinking with the boolean addiction and can answer the question intelligently.
My two main objection to booleans are:
Booleans often produce out of tolerance geometry or other booby traps that can trip you up later. This objection applies to most of the other solid modeling tools also.
The notion that booleans save you time is mostly an illusion (another example of cloudy thinking) When booleans fail users waste an enormous amount of time. Booleans are the biggest waste of time for those who don’t know how to model without them. Boolean users often waste time setting things up for that magical moment. If you learn to model without them you may discover that a lot of the setup operations are not needed.
If you learn to model without them you are in a position to decide for yourself if they are helping or hurting you in terms of productivity. And as an added bonus you get out from under the cloudy thinking and start to see new possibilities and avenues to getting the results you want.
It is no coincidence that new users (and some old users) are often surprised to learn that you can create more robust and accurate models without booleans. How are they to know if nobody tells them otherwise?
What did you do with the surfaces that you used to cut the hole?
Those are the surfaces that would fill the hole.
The point of my suggestion to learn to do these operations by trimming ( or splitting) and then joining is to show you that booleans are no big mystery. You can do the same thing yourself and actually sometimes you can do it better.
When it trimmed the cutting object deleted along with the piece removed within it’s boundary.
A sphere with an intersecting paraboloid:
Pre-select both and run Trim.
Select the portions of each surface you want removed:
Join the two trimmed surfaces into a closed solid:
