Duration of this timer can be set by the number of steel balls, 30 seconds per ball. Only the last ball rings the bell, and the others are just ejected.

You also need

• Steel balls (11-12mm)
• Steel shaft (1.5mm or around)
• Bell
• two screws (M2 - M2.5)
• lubricant

Tools:

• Drill (two diameters, depending of the diameter of the shaft)
• glue or soldering iron
• knife to tune the shape of the escapement
• hammer to insert the shaft to the tight-fit holes
• tap for the screw holes of pendulum weight (I used M2.5 tap and screw)

Caution : the weight of a single steel ball (11mm, approx. 5g) is very light, and it needs careful tuning to make the timer working properly. All holes for axes are just guide holes and you need drilling. Some parts need post-process, for example, pallets of the escapement should be carved.