How to make and solder a metal cone.
First make a paper pattern to neatly circle you desired shape.
Cut out then anneal them to a cherry red colour and let them cool down naturally for a few minuites.
Take your desired shape, here is mine for making the cone, it is a piece of scrap timber, but it could be anything solid enough to support the next part of the process.
Now carefully fold the metal blank around the pattern, until the two open seams line up, I use a wooden cyclinder to aid forming the part without damaging the flat surfaces of the metal.
Carry on forming until you reach this stage, then run a piece of sand paper along the seam/gap to clean up the edges, this will help gain a good connection when soldering.
When your happy with the neatness nof the seam edges, apply the flux along the seam from the inside, not the outside.
Now the metal needs to be wired to prevent the metal from moving/expanding during the soldering process. Start from the widest end and twist the two ends of some plain wire together so it leaves a long tail to one side, slide the wire up as tight as possible and loope the tail over the top edge so it does;nt slide back down again, do this several times as shown, so the ends of the twists are to one side of the seam, try and get the seam gap closed as tight as possible, the smaller the gap the faster it will take the solder.
Now solder the piece using a gas torch/blowlamp, as the metal becomes hot enough cherry reddish add the solder to the seam area and if it is warm enough the solder will automatically flow along the seam.
Now remove the wires, replace the metal onto its former/mandrel and clean everything up, mine was for a garden dibber, metal was 0.70 mm copper sheet, solder was 660 MP silver solder.