Combination Lock: a Five-Disc Drawer Lock (Boy Mechanic, 1915)

Cut five discs of sheet brass about 1/16 in thick and 1 1/2 in across. Drill each for a driving pin 15/32 in from the centre and press the pin in. Notch discs C, D and E for the latch; shape disc B as a cam to lift the latch into its keeper; leave disc A plain with only its pin (Fig. 1).

Inside the drawer front fit a U-shaped metal bracket F carrying a 1/4 in pin G. Thread the discs on it with rubber washers H to M between them so they don't turn too freely. Fix disc A tight on the end of a 1/4 in rod N that passes out through the front.

Make the knob of two pieces of wood screwed together with a pointer between them, fit it on rod N with a washer against the drawer. Paste on a paper dial with division marks and numbers. Fit the latch T in a U-shaped metal piece U inside the drawer end so its heel rests on the disc edges, with its keeper above. To find the combination, open the drawer and turn the knob until each notch comes under the latch heel, noting the number under the pointer each time.