How can I create a sheet metal drawing from this loft model ?

richard_joy

I understand that the sheet metal feature does not have a loft option but did not understand the workarounds. I would like to create a sheet metal model from https://cad.onshape.com/documents/6b84d6ad0575f2aee8f4c1d2/w/0b80712e5763150ee821387b/e/788a026608c0d1dfea8bf1b0

eric_pesty

richard_joy said:

What I am trying to achieve is a polygon at one end that fits in a circle to a polygon with the same number of sides at the smaller end but fits in an ellipse. While it seems to be possible to create the 3d model using loft it does not allow me to generate a sheet metal model from it. When you say "planar" does it mean that the sides at each end have to be proportionally the same ?.

Planar means all 4 corners of the face are in the same plane: another way to look at it is that there has to be a direction you can look at the face where it is just a line, if you can't find it it's not planar!
You literally cannot flatten a face like the one you have in there without stretching material so you wouldn't be able to make this from sheet metal by just creating bends (there is a subset of non-planar faces that can be flattened called developable surfaces but that's another topic!).



 
It should be possible to do by splitting the faces into two triangular faces but the sheet metal tool seems to have a hard time with the sharp corners it creates so it takes some extra work to remove the corners before creating the sheet metal (they can be "mostly" closed up after the fact like this:

https://cad.onshape.com/documents/3013a50090f24bc3f28b0845/w/be90e6c8aab573cdadc8f21a/e/0d4fc58cbac2619d3bfb1ad2

eric_pesty

The four "corner" faces are not planar and can therefore not be "flattened", you need to ensure they are planar first (or split them into two planar triangles but that would be harder to make...)

Something like this (obviously it can't be quite the same shape though...)

https://cad.onshape.com/documents/3013a50090f24bc3f28b0845/w/be90e6c8aab573cdadc8f21a/e/0d4fc58cbac2619d3bfb1ad2

richard_joy

What I am trying to achieve is a polygon at one end that fits in a circle to a polygon with the same number of sides at the smaller end but fits in an ellipse. While it seems to be possible to create the 3d model using loft it does not allow me to generate a sheet metal model from it. When you say "planar" does it mean that the sides at each end have to be proportionally the same ?.

eric_pesty

richard_joy said:

What I am trying to achieve is a polygon at one end that fits in a circle to a polygon with the same number of sides at the smaller end but fits in an ellipse. While it seems to be possible to create the 3d model using loft it does not allow me to generate a sheet metal model from it. When you say "planar" does it mean that the sides at each end have to be proportionally the same ?.

Planar means all 4 corners of the face are in the same plane: another way to look at it is that there has to be a direction you can look at the face where it is just a line, if you can't find it it's not planar!
You literally cannot flatten a face like the one you have in there without stretching material so you wouldn't be able to make this from sheet metal by just creating bends (there is a subset of non-planar faces that can be flattened called developable surfaces but that's another topic!).



 
It should be possible to do by splitting the faces into two triangular faces but the sheet metal tool seems to have a hard time with the sharp corners it creates so it takes some extra work to remove the corners before creating the sheet metal (they can be "mostly" closed up after the fact like this:

https://cad.onshape.com/documents/3013a50090f24bc3f28b0845/w/be90e6c8aab573cdadc8f21a/e/0d4fc58cbac2619d3bfb1ad2