If you have difficulty making a 3D sketch, it can be an advantage to draw a solid one first. This can be used if, for example. you want to make a Weldment structure.
1. Build a Solid with the desired shape. In this example, two Boss Extrude features have been used.
2. Start a 3D sketch.
3. Start Convert Entities
4. Select all the desired edges of the Solid and press OK.
5. Hide the Solid. This can be done by running the cursor over it and pressing TAB. Now you only have the 3Dsketch left.
6. Now you can, for example, make a Weldment structure based on the 3Dsketch.