postfach wrote:If the gears were manufactured in the same way, of the same material, then a straight cut gear will be weaker than an helical cut gear (less surface area to distribute the load). The advantage is there is no sideways load on the bearings.
are you sure about that? I'm not convinced. More surface area just means less pressure on the face, reducing the chance of local yielding (which I've never seen occur in a gearbox). Even if it was the case, helical gears don't make contact with the entire tooth at once, that's why they're quieter - the contact surface moves along the tooth as it rotates, meaning you have a more gradual transition from tooth to tooth. Anyway, gears usually fail because a whole tooth (or many) are stripped off the gear, and I suspect the geometry of a helical tooth would create stress-raisers at the leading edge of the base of the tooth, which would make them more prone to failure at lower loads. Add to all this that because a helical gear has additional axial (thrust) loads on the teeth, you're putting more force into the tooth for the same amount of torque, which would make them even more likely to break