Flat plane that stays flat

Hey All,

I’m wondering if there’s a way to make a plane stay flat?

I’m making a multi-planar model (it’s a sheetmetal fabrication with bends), and need to update it by moving the planar faces without having them quit being flat.

Is there a command or simple method of doing that?

There’s a lot going on with all the many planar faces sharing edges and vertices, so it’s not as simple as I thought it would be. Plus, when I add holes and other features to the basic model, everything gets VERY complicated real quick.

Thanx … Chris

in case you are using solid points for changing the shape this can cause problems if not handled with care creating higher degree surfaces which can fold up the geometry. other that then flat planes which are moved in space should not break from their flatness.

so its quite open at this point what you actually need, a screen shot or a part of your file would help others to help you further. you can just drag and drop images and files into this reply window.

Hi Richard,

Thanx for your input.

I don’t understand what you mean.

Every plane that I create is able to be non-flat, depending on how I move the activated corner point.

I can’t find any plane that stays flat all the time, and adjusts as a flat planar entity when I move one of it’s corners.

Thanx … Chris

use triangles :wink:

can you give an example of what the overall shape is ?

Hi Jeff,
Thanx for the suggestion.
Too bad triangles work the same!
Find attached a pic of my WIP.
When faces need to move in or our or up or down or some part of the face needs to move, it causes the whole model to break. If the faces were fixed planar and didn’t contort when a corner was moved, but moved according to their fixed geometry as a plane, that would make things quite a bit easier.
… Chris

Fender-FrontDriverSide-ORIGINAL3b.pdf (59.3 KB)

how so? triangles are always flat

moving one corner of a 4 corner planar surface isn’t enough info to tell what the other 3 corners should do (if the quad is to remain flat).

you’ll probably need to use a combination of rotating (_Rotate3D) and _Move (being sure to only move points to other places on the plane)

that said, this will only work if the planar restrictions and locations of seam will allow for planar surfaces in the first place.

The difficulty is unless all the edges of a surface with 4 or more edges are moved together the surface may no longer be planar. So the individual surfaces need to be edited as desired and then the rest of the geometry adjusted as needed.

Try this method for editing the shape while keeping the surfaces planar and keeping the holes, etc.

ExtractSrf the surface(s) to be moved.

Move, Rotate, drag, etc the extracted surface(s) to the desired position and orientation.

ExtendSrf edges if needed so that the surfaces and polysurfaces intersect as desired.

Trim the surfaces and polysurfaces as desired.

Continue editIng as above.

Join the surfaces and polysurfaces for a single polysurface.


Thanx for the input.

I tried Jeff’s suggestion before posting in this forum.
Reason I posted is b/c it’s too much work to do that to all the edges and corners when editing the sheetmetal.
I was hoping for something more ‘intuitive’.

The way David says is what I already do, except I use both flat planes and wireframe together. But that method, although less labor intensive than Jeff’s suggestion, is still a lotta work. It took me 5 hours to edit the model in the pdf into a modified shape.

The reason I do this in Rhino is b/c Inventor sheetmetal has limitations that causes the work to be even more cumbersome and time consuming. It’s all about how you set up the model and work it during the design process. But with inventor, once the model is set up, you merely have to change one or 2 numbers on sketch dimensions and the whole model updates. If the changes aren’t too drastic so as to break areas of the model, then the update is instantaneous. But if parts of the model break, then there’s some reworking involved, which can sometimes be very time consuming. When that happens, the design process and CREATIVITY drop below zero, due to most of the brain power being consumed on working around the software’s limitations.

I was hoping for a more intuitive method of working with a solid or surface model that can use “push-pull” on vertices/corners and/or faces and/or edges to suit my design iterations.

Is this possible in Rhino?

If not, is there a program that works like that which I can use for concept design, and still be faithful to dimensional accuracy?

Thanx … Chris

no. its not a software issue but a geometry absurdity. or lets say a way of thinking how it could work in reality and having to figure that the pixels and vectors of our computers are far more flexible than one would want to have.

if you work with points from a plane then the only thing you have to maintain is that you move 2 none diagonal points at the same time. thats as intuitiv as it can get to keep a plane plane.

implying that you have a degree 1 surface with 4 corner points only of course. you can also use more points on a degree 1 surface if you follow the rule not to move diagonal points and always a whole row at once.

Hi Richard,

Thanx for your input.

I have to disagree with you.

I’ve been doing this for over a decade in Inventor.

The only thing is, this piece of sheetmetal has 2 features in it that won’t work with Inventor sheetmetal.

That’s why I had to use Rhino.

There’s gotta be a program out there that is intuitive.

There sure is a lotta hype about all these intuitive programs and what they can do.

Only thing is, all the people in marketing know nothing, and all the guys doing the demos lie like a rug.

So finding honest appraisals of software is next to impossible.

show me a few screenshots how you do that or maybe a video. i am getting the feeling we are talking about different pairs of shoes here. the only way this would work if all points are locked parametrically and reposition automatically according to the laws of geometry when you move one point basically what i explained above.

in your logic triangles create higher degree surfaces and rectangulars not hmm :smiley:

Yes, well this is the way that parametric software with constraints can work, if you specify that a particular element must remain planar, then the software limits what you can do with it so that it always remains that way. I also imagine that sheet metal software is built around this as generally you are punching and folding flat planes.


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Mitch is getting what I’m saying.
That’s what I wanted to duplicate in Rhino.

Actually, if possible, I wanted to make it even more simple and intuitive w/“push-pull” on faces/edges/vertices to change geometry. Start w/simple cuts and work the design w/push-pull operations till getting it to where we want it to be. After that, we can break it down into a fabricatable part.

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Unfortunately, as basic Rhino is not parametric, there aren’t tools like constraints, so most of what you want is difficult. You might be able to do something via Grasshopper and Kangaroo2, as not only is there a constraint solver, but I seem to recall you could also push/pull things directly in the Rhino interface - but I don’t really know what’s possible there, as I’m not a user…


Thanx Mitch.
That’s what I needed to know.
Just figured there may be a way w/o having to learn a whole new work-flow and interface w/GH or K2.

Here’s my ‘workaround’:

Make a wireframe w/only lines that are not connected to each other.
That way all the lines move w/o control points (except their end points).

Then make faces using ‘surface from planar curves’.
That guarantees planar faces.

Work everything as triangles, even though the planes may have more than 3 sides.

Once the model is totally perfect:

  • All vertices connected, w/no stray end points,
  • All shared edges coincident w/no parallax,
  • All faces perfectly flat …

Then export only the faces to step or iges,

Then import into my parametric cad program to make sheetmetal out of it + make a drawing from the 3d model.

That’s a LOTTA steps, but it’s what it is.
I was hoping to find a way to use OLE between Rhino and Inventor, but can’t find a way to do that.
Also, I can’t find a way in Inventor to “derive” an imported surface model, which would be a potential work around for this problem.

I just hate having more than one program to do the job I need to do, b/c down-stream revisions/changes really screws up the work-flow. It forces you to start all over again. What a PITA!

That’s my skeletal work-flow for going from scan/digitize > Rhino work features > parametric solids modeler.

What I’d like to have is a way to connect Inventor to Rhino so that changes in the Rhino model will translate automatically into Inventor (good old fashioned OLE-like behavior).

Cheers … Chris

Hey Chris

What you’re asking is a question I’ve often tried to solve myself. One way is to make a custom tool that sets the CPLANE to three points of your existing shape, and then to SETPT the 4th point to the same Z coordinates as the other 3 in the cplane. This is cumbersome. It’s a capability seriously lacking in Rhino.


Thanx for replying.

Maybe this is why Inventor lacks surfacing tools, and why Adsk refuses to spend the $$$ on adding it to their program?

Or maybe they’re skulking around the market looking for an unwary victim to buy-out and cobble into their already over-loaded mound of code?

Let’s hope the McNeel folks will take a look at this thread and consider adding some sort of code to Rhino to bridge this gap. I also want some kind of “live link” between Rhino and Inventor that can go back to any Inventor version. That way, what I make and edit in Rhino will always update automatically in Inventor.

What do you think?
Is this a “market share” that’s lacking in our design/engineering world?

There are a few features like that, for example an easy unbending / tagging tool for sheet metal. I guess at the end of the day Rhino is a generalist type program and not specifically designed for any one of the numerous things people use it for.

Yeah, UnrollSurf really sucks, b/c it breaks apart a formed surface.
So you can never get a flat pattern that you can use at the steel mill.
My work-around for that is the tedious re-construction of all faces to which apply Join
But that’s just added work, considering it happens automatically in the parametric program I use.
The thing that complicates the matter is the bend plane or k-factor used.
Man does that complicate the process, b/c of 2 things:

  1. The entire surface must be offset equal to the k-factor distance from the bend face, which can create an enormous mess (!), and
  2. If the customer changes the sheetmetal thickness, you have to start all over again (!!)
    Anyways, if wishes were dollars in the software world, I’d be rich already!