Input: the spiral gear of 1 start (Z1).
Output: the spur gear of 18 teeth (Z2).
Axle of the spiral gear must be laid in the front face of the spur gear.
The helical angle of the spur gear teeth must be in accordance with spiral direction of the spiral gear.
1 rev. of the input corresponds 1/18 rev. of the output (Z1/Z2).
The number of starts can be more.