Purchase or find untreated lumber, such as poplar or pine, which is 1 inch thick by 3 inches wide and screen mesh. The size of the mesh will depend upon the rock or mineral you are hunting for. Often an old window screen will work just fine.

Measure four lengths of 12 inches and saw along each of your measured lines to create four even pieces.

Place two pieces of wood upright, on their 1-inch thick sides, and make the ends meet each other, forming a 90 degree angle.

Screw the ends together so that the corner holds sturdy. Repeat this process until you have a complete, box frame measuring about 12-by-14 inches. Each corner will require about 2, 3/4 inch screws. You can use nails if preferred.

Cut out a square piece from the screen mesh that is about the same size as the bottom side of the box and staple it to the bottom. The screen should be just a bit smaller than the bottom or you will need to trim the excess screen hanging out from under the box once finished.

Saw 12 inch long, 3/4 inch thick bands of thin wood and gently nail them into the bottom of the box to cover the raw edges of the mesh. Alternatively, you could glue the pieces down with a durable wood glue to complete the sifter.