Trim Solids

I tried to trim a cone using iso curves but I cant select the surface on the cone although using the same command, it works on a sphere?

Is the cone a closed polysurface with a cap? If so explode the cone and then try splitting the desired surface. The isocurve option of Split works on individual surfaces but not on polysurfaces.

Above is based on Rhino for Windows but I believe it is valid for Rhino for Mac.

not sure but if you want to cut a piece out of, or the tip of, a solid that is a cone, pyramid, or cube, how do you do it? it doesnt work with the trim Isocurve command

btw, I watched Kyle’s video on how he made the earphones and followed the commands including the splitting of the sphere at the front, which works fine. Som, why the difference when you use a cone/pyramid?

Hi Bip - a cone is a polysurface - multiple surfaces joined together - & only single surfaces can be split with isocurves, so you need to either ExtractSrf the surface to split from the polysurface, (or Explode) or use something else, like a CutPlane to split.


it worked with the explode command, thanks. but why is a sphere an open polysurface and the cone a closed one? anyway, appreciate the help, thanks.

thanks, appreciate it

A Rhino sphere is neither open nor a polysurface - it is a single surface and is closed.
Note that all NURBS surfaces have 4 edges. In the case of a sphere, two of those are collapsed into a point (singularity) and the two remaining edges join each other in the seam of the sphere.

The Rhino cone is a closed polysurface that consists of the conical surface and a base surface.

however much I like Rhino, which I do, the difficulty I have had is that it seems that the functions of the command are counter intuitive. That along with the use of language where english words are used on places where the descriptions of supposed function and the word used make no sense.ut this is a programmer problem and not limited to Rhino. For example, the description used below is by definitions in an English dictionary contradictory. A sphere doesnt have edges and NURBS are not Rational or Irrational. You have to Explode the cone to use the trim command…all which means that you have to memories everything in order to do the work which is a huge barrier to entry for a bigger audience, and for people that don’t have the undress of hours to go through tutorials to memorize all the commands…its too bad but once you know them, its great fun, I assume…

All NURBS surfaces (hence all Rhino surface objects) have edges. They can be open (naked) edges, closed (seam) edges that are joined to another edge of the same surface, singular (collapsed to a point or pole) edges, or manifold edges (joined to a different surface).

Irrational is not necessarily the opposite of rational. Rational pertains to the quality of being able to apply different weights to control points here. That is the “R” in NURBS.

“NURBS curves and surfaces are generalizations of both B-splines and Bézier curves and surfaces, the primary difference being the weighting of the control points, which makes NURBS curves rational.”

if you read the rest of the message, I gave the example of the use of the word “rational” as an example of how the dictionary definition of a word is changed and in some cases used arbitrarily in an way that does not explain the function or command, confusing the message. Edges on spheres is one of them…

Well, CAD in general has many technical terms that are used to describe various components and procedures. These terms may also have other meanings in other contexts. It is not rational in this case to try and force literary definitions for these components.


I agree, but the point I am trying to make is that when the word “edge” for example is used in part to describe spheres, and that they have two, presumably, reading this, a beginner will look for an edge, or two. Once you have figured out that there isn’t one, in the traditional definition of an edge, you need to sort out what command to use to accomplish the job, which is not an intuitive process in this case. Using Kyle’s videos for example, makes the job a lot easier, they are great, in fact. But there is nothing as far as I have found, that tells you about the fundamentals of how the edges of sphere behave and how they are different from those in a pyramid, and more importantly, why. It seems that cutting or trimming a solid sphere should be no different from trimming a pyramid, its a rank beginner kind of action but the solution isn’t. Nor are the words leading you in the direction of a solutions.

But this doesnt solve anything; the product is what it is and so is most technical software. I have developed a bunch myself so my experience with programmers is fairly long. Having said that, the tutorials, customer service and the forum help at McNeely is top notch so eventually I will hopefully get beyond the rudimentary…

Just keep at it!

And, no, nobody around here has any way to influence the vocabulary that is used in CAD.
And there is no instant - nor necessarily easy - way of learning all there is about this.

In that spirit…

It is crucial that you understand that a sphere has four (4) edges. As do all NURBS surfaces. Two are collapsed to points at the poles and two share the same space.

It isn’t - if you use the standard Split or Trim commands, which work on both single surfaces as well as polysurfaces, open or closed. Splitting or trimming by isocurves only works on single (unjoined) surfaces.

Imagine you have a knife, a saw and a shears in your toolbox. All three tools are designed to cut or trim objects. However, neither the knife nor the shears work very well (if at all) to cut a piece of wood; on the other hand they work well to cut paper, whereas the saw doesn’t really… It’s all about learning which tools are appropriate for which job.


There may be something wrong with my settings or Mac but when I try to isolate the commands, they don’t work. I got Solids, choose a Cone, and then try to use either Split or Trim, I don’t get any results regardless of choice of using Point or Isocurve…

Hi Bip - that is expected - points and isos cannot trim a polysurface - only unjoined surfaces can be split with “Isocurve”, and only ‘free’ curves (not edges or isos) can be split with the “Point” option.


right, now, in trying to figure out the difference between a sphere and a cone, I draw cone from the Solid menu, 12” tall and 6” wide at the base. when I select either Trim or Split to cut the upper half off the cone, nothing happens.

Hi Bip - what does the command line say? Do you also have an object to trim with?

A sphere: one surface, closed
A solid cone: two surfaces, closed, in Rhinospeak, a polysurface - the cone shape and the planar cap on the base.


I know this is bonehead Rhino, but how do I split the cone?