Creating a swaged hole in the bottom of a fuel tank.

Ebby wrote:
Dear All,

I am starting to build my center section fuel tank and need information
about how to swage holes in the bottom of the tank so that I can edge weld
the six fittings specified in the plans. Four of the fittings are finger
strainers and one is for the sight gauge. There is one more hole on the top
for the filler. As there are only six holes in three different diameters, I
was thinking about doing it using simple hand techniques rather than
expensive tooling.

Here is my idea. The tank is .090" 5052. I planned on drilling holes
(.180+flange dimension) undersize in the aluminum. Then centering the holes
over 3/8" steel plate with holes .180 oversize, then use a polyethelene
bossing hammer to swage the edge of the hole into the female die hole. The
holes in the female die would have the edges relieved to accomodate a bend
radius. It might be time consuming but educational.

Any advice or previous experience to share


A piece of 1/2" plywood and a couple chunks of 2x4. Tack plywood to one
of the blocks and use a small hole saw with a 1/4" centering bit to cut
the inside diameter of the swage. The piece that you dig from the hole
saw goes on one side of the aluminum. Use a bigger hole saw, centering
on the same 1/4" hole, cut the outside diameter of the swage, then drill
the 1/4" hole all the way through the block. Drill a 1/4" hole through
the other block. Drill a 1/4" hole where the swage will go.

Thread a sufficiently long bolt through a fender washer, the block with
the plywood attached, the aluminum, the piece you dug out of the small
hole saw, the other 2x4 block, then another fender washer. Spin a nut
down to extrude the swage.

I don't know if this will work on .090, but I've used this technique on
thinner material.