A resonator guitar has a metal cone where a typical acoustic has a sound hole. This gives the guitar a characteristically bright and metallic sound, with significantly more projection that you’d get from a sound hole. The cone is mounted in a sound well, which adds to the resonance by transferring the vibrations from the cone to the back of the guitar. You can build your own resonator assembly to use when converting your acoustic into a resonator guitar.
Remove the lid from the biscuit tin. Set the tin to one side; you use this later as mold for the sound well.
Cover one side of the lid with aluminum foil to protect the surface from burns.
Put on a pair of heat-proof gloves.
Heat the center of the lid with a heat gun and gently tap the metal with a hammer until the center of the tin is concave. The concave shape adds to the resonance. Leave the tin to cool for 30 minutes. The tin forms the resonator cone part of the assembly.
Remove the gloves.
Measure the circumference and depth of the biscuit tin with a piece of string.
Cut the scrap wood so its length is equivalent to the circumference of the tin minus 1/2 inch and the width is equivalent to the depth. Being 1/2 inch shorter in length than the circumference of the tin means the tin lid will be slightly over-sized. This is preferable. Conforming the wood to the dimensions of the tin is a convenient way of ensuring the lid is an approximate fit.
Place the biscuit tin on its base. Cover the wood with foil. Lean the uncovered side of the wood against the tin.
Put the heat-proof gloves back on.
Apply heat to the wood and gently bend it against the tin. The heat softens the wood and the tin shapes it in a circle. Feed the wood around the tin as if wrapping the tin in wood.
Continue to apply heat to the wood and press it against the tin until the wood takes the form of a circle. This process is very similar to side-bending, used for shaping the side panels of acoustic guitars.
Glue the edges of the wood together and fit in a bench-clamp for four hours to dry. The wooden ring will form the sound well.
Remove the sound well from the clamp. With a plunge router, make a series of holes around the center of the edge. They needn’t be precisely equally sized or spaced, because they won’t be visible, but try to make them as similar as possible.
Place the resonator cone on top of the sound well, so it forms a bowl. Cover it in foil.
Put on the gloves.
Apply heat to the center of the cone again. Gently push down into the cone to increase the depth and reduce the distance between the edges. The more concave the cone, the smaller its diameter. As the cone becomes more pronounced, the diameter decreases. This will bring the edges toward the top of the sound well.
Stop heat-shaping the cone when the edges are flush with the top of the sound well and the cone sits snugly on top of the sound well.
Bend the lid from the non-decorated side. This is the side that will face outward when fitted to the sound well.