I’m designing a sheet metal sign. The model accounts for material thickness making it a solid. Is there a way to unwrap/flatten a solid to prepare the drawing for laser cutting? I’ve tried unroll and flatten with mixed results, but maybe I was not using the tool correctly. The work around I am currently experimenting with is deleting all the surfaces accounting for material thickness, so the sign is made up of only outermost surfaces (no longer solid, but a polysurface) and then running flatten or unroll.
Hi Justin - that is one way to do it, however, strictly speaking you also need to take into account the ‘k-factor’ at the bends wich means the unroll will/should be of some inner surfaces within the thickness of the material.
This plug-in can help in extracting the inner or outer series of faces to unroll, if you are just going to unroll those and come ‘close enough’. Probably set Copy=Yes, I think it is No by default.
Ok, so just for clarification; unrolling the interior surfaces will give a more accurate k-factor than unrolling the exterior surfaces?
Does the plugin keep all of the planar surfaces dimensionally accurate, but lose some accuracy in the bend areas? If so I could probably just manually rebuild the bend areas to account for exact arc length.
The k-factor describes where the neutral surface is located between the inner and outer surfaces. For improved accuracy you will need to use an intermediate surface located using the appropriate k-factor.
Hi Justin - the plug-in I posted is simply a shortcut to ease the tedium of getting all of the tangent faces, inner or outer.
Neither inner or outer is correct - probably a mid plane would be more accurate than either inner or outer but for any given material, thickness and bend radius the theoretical neutral surface will vary - it lies someplace within the tickness of the object.
So effectively would the neutral surface be an offset polysurface existing midway between the outermost and innermost polysurfaces and unrolling this mid surface would be the most dimensionally accurate?
Hi Justin - put the RHP file anywhere that makes sense, right-click > Properties to un-block it., then drag and drop it onto a Rhino window to isntall. The command is
ExtractTangentFaces
BTW, you will want to UnjoinEdge these edges before unrolling:
Midway would be better than the outer or inner surfaces but usually the neutral surface is located closer to the inside than the outside of the bend. It depends on the bend radius to material thickness ratio, material properties and bending method. I high accuracy is needed consult with someone with experience, which I am not.
Using a bending machine this would probably work fine for just two opposing sides but all four sides is going to be difficult unless you have a special magnetic tool like in this video.
I was wondering if there was going to be bending issues. Is it possible to bend them all at shallower angles and finish bending manually by hand? The sheet metal is pretty thin.
