Many common cooking oils are derived from pressed seeds. Canola and sunflower oil are both popular. Although they are easily bought, pressing them at home will yield a pure oil free from additives, preservatives, or chemicals. With a bit of space, a family can grow the seeds themselves. A 232 square metres (2,500 square foot) plot of sunflowers, for example, can produce approximately 13.5 litres (3 gallons) of oil. It is also possible to purchase special oil seeds. In both cases the seeds must be finely ground before pressing. Building a press at home requires plenty of tools and some welding ability.
Buy a cylindrical 2.7 tonne (3 ton) hydraulic jack. These are available from most auto and hardware shops.
Cut two 61.25 cm (24.5 inch) lengths and one 16.25 cm (6.5 inch) length of 4.3 cm (1.75 inch) metal tubing. You will need a carbide blade for your bandsaw or circular saw to cut through the tubing without dulling the blade.
Cut a 13.7 cm (5.5 inch) long piece of steel bar to form the crossbar between the pipes, again using a carbide-blade saw.
Cut two 20 cm (8 inch) lengths of angle iron (flat faces joined at a 90 degree angle). These will join the bottom of the two tubes to the small tube and join the whole frame to a wooden base.
Stand the long tubes on their ends 13.7 cm (5.5 inch) apart, with the short tube standing between them. Use an arc welder to weld the 13.7 cm (5.5 inch) piece of steel bar between the tops of the tubes. Weld the two pieces of angle iron to either side of the bottoms of all three tubes, making a rectangular frame with the small tube in the middle of one short side.
Grind down any rough surfaces and paint the frame to seal any last shavings in.
Drill holes through the angle iron and pass screws through them to attach the frame to a wooden base. Paint and lacquer the base to finish it.
Make a pressing cylinder by welding one end of a steel canister shut with a metal disk cut from your plate steel. Pierce the sides of the cylinder with a series of holes and file down any rough edges.
Make a piston for the press by cutting out a metal disk that fits tightly inside the pressing cylinder. Weld a short length of pipe to the top of the disk; the pipe should have a diameter just wide enough to fit over the end of the short pipe in the middle of the frame.
Cut off the bottom 3.7 cm (1.5 inches) of a plastic jug. This will serve as a collection tray for the oil. Cut a circular hole in the centre of it so that it fits over the small pipe in your frame, and cut a small slot for the oil to flow into a cup set below the tray.
Fit the collection tray over the small pipe, then fit the piston disk over the end of the pipe. Pile the ground sunflower seeds on the piston disk, then place the pierced cylinder on top of them.
Fit the hydraulic jack between the top of your frame and the closed top of the cylinder. Centre the jack's extending piston on the top of the cylinder and pump the jack. The pressure of the jack will force the cylinder down onto the ground seeds sitting on the piston disk and squeeze out their oil, which will drip down from the holes in the cylinder's sides into the collection tray.