Dear Siti Khadijah,

First of all, a spur gear is a special case of a helical gear where the helix angle equal to zero.

Efficiency: a spur gear is more efficient if you compare it with a helical gear of the same size, because helical gears have sliding contacts between the teeth which in turns produce an axial thrust of gear shafts and generate more heat. So, more power loss and less efficiency.

Easy to assemble: Spur gear teeth are parallel to its axis. Hence, spur gear train does not produce axial thrust. So the gear shafts can be mounted easily using ball bearings. On the other hand, helical gears generate axial thrust so the bearing arrangement of the shafts in this case should handle the axial thrust along with radial thrust. You may have to go for a roller bearing or a thrust bearing in this case.

Silent operation: In a helical gear train, the teeth engage a little at a time rather than the entire face at once. This causes less noisy power transfer in case of helical gears.

Strength: For same tooth size (module) and equivalent width, helical gears can handle more load than spur gears because the helical gear tooth is effectively larger since it is diagonally positioned.

As a conclusion, you should go for spur gear for simplicity and efficiency. On the other hand, helical gear should be considered for smooth high power applications.

For more details you can read the follows book "Cylindrical Gears Calculation – Materials – Manufacturing"

Best regards,

In general, the helical gear is better and the cost is a little difference.