What type of gears does a pillar drill and lathe use and why these types instead of a more simple type of gear?
I assume you mean geared head machines.
Gears next to spiral cut teeth are mostly used.
1. Spiral gear teeth can transmit more power, as they are spreading the load between several teeth rather than one tooth within a simple spur gear.
2. Spiral cut gear teeth transmit power at a more constant velocity.
3. Spiral gears run much quieter than straight toothed gears.
The only disadvantages with spiral cut gears are the finish off thrust produced, but this can be offset by having alternate gears cut the contrasting hand. Also because of the continuous sliding action of the teeth, better lubricants may be mandatory.
If bevel gears are included for transmitting power at an angle to the driving force, spiral cut bevel gears will also have similar characteristics to the above.