Flattening a 3-d helix

helix.3dm (226.2 KB)
Having trouble flatening part and keeping the side surfaces perpendicular with construction plane and the upper and lower surfaces perfectly flat. This part is to be cut on a flow waterjet and that software does not like what I have tried


If anyone can help that would be GREAT

@bob5 How will the part be made. I assume the part will begin flat on a plane parallel to the construction plane. It will then be cut using the waterjet, and then formed into the 3D shape. If so how will it be formed into the 3D shape? Most methods of forming will not keep the sides perpendicular to the original construction plane as in your current model. Instead the sides will stay more or less perpendicular to the upper and lower surfaces of the part.

It will be heated on a form and twisted into helical shape. I just need to get it flat, I think the waterjet has shown the curved sides in red because they don’nt line up after I flatten the part,

Also David, this is rhino 6

What information does the waterjet software need? Does it need anything more than the shape of a surface, and location, angle and diameter of the holes?

How did you flatten the part?

flattening it is trivial. just construct two angled c-planes (one for the top and one for the bottom, thickness distance apart) and use setpt (on z, to c-plane) on (selected) control points of your surfaces. you might need to do a few more adjustments, but those are trivial as well

but i wouldn’t recommend full-heartedly this method. the difficult part is to make sure that you get that shape under bending during manufacturing process.


on the left, the flattened surface,
on the right, the objects to construct the cplane → what i did here is use a line from the middles of the end edges and extruded it in the x direction
then i used c-plane to object, i selected the surface → setpt → check only z and align to c-plane

a simpler way is to just use the world xy plane → which in effect creates a projection-> which reduces the lengths by quite a bit

after which you can simply do an offset srf

you can also use flow along surface.


here i constructed an arched surface (right) from the length of the inner edge, with the proper width, and used the bottom surface as base and the constructed surface as target

but again, unless you know how the deformation during manufacturing behaves, there’s no way of know how you should flatten it

Which is why flattening is not trivial.

the geometric methods for flattening that piece are trivial, which is what i meant.

but indeed, figuring out the parameters under which to operate is a hard problem. there’s specialized software for that which you’d use to figure those out in an interative process. this process is indeed not trivial

Unrolsrf and flow along srf

does it preserve the edge lengths?

yes, preserves lengths

@bob5 You may want to use UnrollSrfUV insteadof UnrollSrf.

UnrollSrfUV does a better job of keeping the same UV mapping than UnrollSrf.

UnrollSrf can be a bit more accurate in the unrolling but as you shape as you have modeled it is not exactly developable the difference between UnrollSrf and UnrollSrfUV should not be significant.

@adel.albloushi UnrollSrf and UnrollSrfUV will preserve lengths and angles if the input surface is developable. If a surface is not developable then it is impossible to unroll / flatten it without some distortion. That is how the geometry works; not a limitation of the software.

I have to admit it didn’t cross my mind to check if the surface had any gaussian curvature. Now that you mention it it should have been obvious from a single glance that it’s a ruled surface… :sweat_smile: