What command to turn a simple L bend in e.g. 2mm sheet to a plan of the unbent sheet?


A sheet of metal when cold and bent through 90 degrees undergoes stretching of metal at the bend. I think I am right in saying no compression occurs.
Lets take a simple portrait shape 100mm tall x 50mm wide, 2mm thick from our shelf of metal bits !..and bend it on our workbench through 90degs and internal radius 5mm at a line parallel to short edge half way along its length (so 50mm down from top), we now have an L shape each face 50mm square ish.
If we then model this as a solid, then wish to show it as a plan before bending, would UnrollSrf or Smash be best to create the rectangle, which should be our exact 100 x 50 again. We dont want the length to be the stretched side of the metal, or the centre of the metal.

I tried both and explode and assembling bits gave me the pre bend shape.

is there a way of doing this without having to place bits together and measure and do maths, just get a 2D plan of the unbent metal object ?

Test accuracy smash v unrollSrf unbending sheet metal.3dm (304.6 KB)



Hi Steve,

I’m currently working on a project in grasshopper that automates this process. In my case I need to take something between 1/3 and 1/2 for the neutral axis. Taking inner surface bends is only possible with thin sheet/small radii. What you can do is extract the inner surfaces in grasshopper, find the correct edges and move the surfaces to each other, join and unroll. That’s basically my process in short.
In my project it gets a bit more tricky as I have Z-bends, so I need to take both offsets and mix/match them together.

here is a simple example: (using lunchbox unroll)

unroll_forum.gh (15.0 KB)

I dont have grasshopper though and that chart thing is completely baffling to me, may as well be egyptian language.
Z bends, ah yes, the inner radii and adjoining surfaces but then the next is the other side so take surfaces from either side of that one. If its a top hat stiffener in a spitfire more fun again.

as for a metal twist…!

If you create a ‘code’ that automates it, which I could run as a command or whatever the pick and run method is, then BINGO.
is the result then bale to be just worked on in normal Rhino3D ?
Not sure what Grasshopper would cost me though , I have little use of it and time to go learning it. and money.
trying to save for V6.
and for turning win7 to a win10 PC.


you have Rhino 5 right? you can download it still for free from grasshopper3d.com

time to learn new stuff, it’s exciting!

Hi, free…excellent
learning, I love learning, I just dont have the time at the moment, one would think being in lockdown creates time but I am effectively always in lockdown as never enough time in the day for all that I have to do, tons of stuff overdue by years, sat at PC from 11am till 1am every day, so tasking myself with learning another prog just wont see it happen, I have to find time to rebuild PC, last OS move took 3 months and was saved by classic shell, I was on verge of giving up, Msoft dont use PCs the way multi-skilled users do, it even wrecked the typefaces, went from jet black to multi-coloured, they had ditched the font controller XP had, not good when doing graphics. Change for changes sake, and as for all those blocks on the screen…got round that asap !

for learning I need well spoken in ENGLISH video tutorials, step by step follow along to a course with supplied tutorial files. I find videos on things but all done by different folk, that have no particular follow order, like reading chapter 7 then 3 then 11 then 2 in a book.

maybe Grasshoper has a tutorial video course, need to look.


so you’re sitting at your pc 12 hours a day and have no time and no money? Arghh… time for change

what better place to start then to learn from the creator himself?

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a download for unfolding bent sheet inn rhino, though he has videos for inventor, solidworks, autocad, rhino no video. always the other players get looked at first.


v5 and v6

I wondered if Autocad had a folding ability, found this site from spotting this video in youtube.

he doesnt do a video for the rhino one, though the autocad prog he videos for, youtube shows other interesting plugins they do.

though he needs to talk ! as others note. !

has anyone used the unfold plugin for rhino ?

I wonder if he can do a fold plugin. ?

I have asked him for one for Rhino. (this my other thread about bending)

I now see this

and this and note Vincenzo doing it the hard way as I am.

so why after all this time is Rhino not adept at bending sheet, and folk trying to do plugins and is grasshopper the way or could commands exist in basic rhino ?


just guessing, but I think there are a couple of reasons:
-there are already plenty of tools on the market that do this really good
-those tools that have this use a parasolid modeling kernel or something as robust.
-it takes a lot of effort and resources to get this done right

furhermore, I found Rhino for certain things more appropriate than for example Solidworks, as it is more forgiving. Some things that are unrolling perfectly fine in Rhino, SW will complain about and then you’re stuck. In Rhino you’re never stuck.

Several different items:

How to unfold a thin surface.

Where to place the “neutral surface” to use in unfolding sheet metal calculations to best represent physical reality. This question has been around since before CAD and there is not single, universal answer.

What modifications to make to the results of unfolding a neutral surface to better represent physical reality. This also depends on the particular circumstances and does not have a universal answer.


I hope something useful comes of these two.