The principle is pretty easy. Two pieces of 18mm mdf. Cut matching holes in them the shape of the bulge. Sandwidge the ali sheet between them and clamp well. The ali needs to be about 50mm bigger all round than the hole. Belt with a soft headed hammer.
To make it easier you can anneal the ali first. Smear if with bar soap. Heat it with a blow torch until the soap goes brown. Allow to cool. Bar soap goes brown just before the melting point of ali so don't overdo it!
Robin
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