UnrollSrf Working With Plate Steel


I mainly work with plate steel for welding and cnc plasma work. I use unrollsrf to extract the surfaces. I have a lot to learn but I have to start somewhere.

Here are the steps that I took to draw the object.

  1. polygon
  2. planarsrf
  3. extrudesrf
  4. unrollsrf

If I select poly surface, then it extracts 9 separate objects. (incorrect for what I need)
If I select surface then it extracts just one object (correct)

My question is…Is this the right way to do this? That is one plate of steel. Is there a way to combine ‘surface’ and ‘polysurface’ so that it is one without loosing the thickness of the object (1/2")

Thanks in advance for helping me!

Hi @flashc5

If you want to unroll only one Srf, Sub selecting the wanted Srf on the PolySrf should work
( tested on Rhino 7 ).

If you want to unroll more than one Srf from the PolySrf :

  • you may run UnjoinEdge to separate the wanted PolySrf edges.
  • Then run UnrollSrf ( Explode option off )
    This way you should be able to lay out on the ground various scenarios.

Hope it helps…

Rodolfo Santos

This is a known limitation of Rhino, but it enables the functionality to unroll a polysurface that represents a multi-plate part, for example a box.

Thank you for the responses.

I just want it to unroll as one object. It wont ever be anything more then a single plate. When I am drawing I need the thickness to be there but when I go to unroll and cut it out I only need the one with the green arrow below. I just want to make sure this is the best way to do this in rhino (selecting ‘surface’ or if there was a more preferred way)

Also, how can I fix this.

It is suppose to be a solid piece of sheet metal 1/2" thick but from this view it looks like it is a solid plane with a flange around the outside. How can I make this a solid piece?

Once you extract a surface, you get a hollow object like in your screenshot. _Cap can close it again.

To me it makes no sense to unroll something that is already flat. Simply take the curve you used to generate the extrusion for your cnc cutting.

I highly recommend to make a display mode that shows all naked edges in different color.


If I understand well your intent, you want to lay out on the ground the silhouette of a bunch of surfaces to be cut via any CNC process ?

Rodolfo Santos

I am not very good at explaining but I will try my best

I buy my metal by the sheet

which has thickness. I am struggling how to best handle this thickness in rhino. So when I draw a 3 dimensional object in rhino I need to account for this thickness so that the measurements come out correctly

So when I draw a box that thickness matters (please see the top view. not all sides are the same length)

I am new to rhino so I am trying to figure out the best way to handle this thickness while being able to extract that to a cutting program. (like rhinocam or enroute that will handle the cutting)

(in the picture above, there is only 4 sides, not 8 sides)

The end result is to get it to unroll to this. (Rhino unrollsrf will extract the sides and then I will import the dxf into this program)

Notice how 2 sides are smaller then the other two (because of the overlap) When put together the box is the same size.

I am just curious what is the best way to handle this.

I think you should look at the Level 1 and 2 Rhino training, as this is not what people are usually asking about when they talk about unrolling steel, they’re usually wondering how to unroll shapes with bends or a developable surface like a boat hull. This is…just basic 3D modeling. It seems a huge waste of time to actually model the plate thickness, I would just model one surface per plate–again people modeling sheet metal parts often make their surfaces represent the middle of the sheet, I don’t know if that makes sense for your situation or not–then it’s super-easy to trim and extend to account for thicknesses when you’re ready to flatten as it’s just surfaces instead of solids.

Also if you know someone who uses Solidworks, it has a great metal bending tool. —-Mark

I dont do much bending but solidworks is out of my price range.

Hello - if you make a box like this:

Then all you need is the inner or the outer face of each of the five panels - lay those flat.

Does that make sense?



Thank you for the update.
Your explanation is perfectly clear and your question is to my humble opinion, interesting.

@pascal yes, it sounds like there is a need for a one step or simple procedure to lay out on the ground a set of faces contours ( at the edge of a nesting request ) …

Rodolfo Santos

With boats, we deal with this all the time. Generally we just model the surfaces on the moulded side of the plate and don’t bother thickening.

However, it would be amazing to model the solids and not have to deal with subsurface selection at the time of unrolling. So, I have had a thought that may achieve this. Assign a subsurface (or set) from the closed polysurface that would be the mould side to be unrolled during modelling. Ideally this would be the original surface that is thickened to create the solid. When it came time to unroll the part just pick the closed polysurface to unroll. Rhino then resorts to unrolling the subsurfaces that were previously assigned as the mould side. Maybe these mould surfaces could be coloured differently.

At least, be able to use UnrollSrf with more than one Srf would be a good progress.
This way the user could pick a set of surfaces on any PolySurf in one step …

Rodolfo Santos

For simple flat objects there are different ways to speed things up:

You can model without thickness and use Thickening render effect to display thickness.

You can also model with thickness, lay things flat by remapPlane and DupfaceBorder to generate the outlines for cnc.

You can make a grasshopper script that listens to your rhino file with a geometry pipeline and have the surfaces you draw thickened and lay flat automatically as you design.

I like that idea.