A 500 mm long stick. 20x20 mm
A small can
A bit of strong, twinned string
Tiny pieces of hard wood 4x4 mm
Mark the length of the can.
Fasten a nail in the other end. Let it stick up about 15 mm.
Fasten it with two small nails.
Glue the first fret that will keep a distance between the fretboard and the string.
Tie a washer in the end of the string.
Drag the string and tie it as tight as possible around the nail.
Divide the length as the image shows for a blues tuned canjo. Use other intervals if you like.
Glue frets on the fretboard.
Decorate the canjo if you wish.
You can use the washer to tighten the string by turning it.