Anybody know the advantages/disadvantages between helical and straight cut gears? Which do you prefer in your transmission?

 

As I recall helical gears have more surface contact when the gears are meshed.

 

straight cut gears are usually stronger, but much more noisey, the helicut are quiet but wont take as much abuse

 

Yes, helical cut gears will be much quieter.

 

Mike is right, of course. The reason straight-cut gears are stronger is that the contact area between the two teeth is actually a line that is the full width of the teeth, which helps to spread the load evenly across both gears. The increased noise (vs helical) is a result of the fact that the meshing action is more abrupt: the entire tooth comes into contact with its mate instantaneously (smack!). Conversely, in a helical mesh the contact area is a single point which, as the two teeth come into contact, begins at one end of the mesh and then wipes down the whole length of it before the teeth part. As this mesh is parting, the next mesh is initiating contact, and so on. Obviously, this process is smoother and therefore, quieter. But that single-point contact area concentrates (and increases) the load on a smaller area of each tooth.

As you might imagine, straight-cut gears are also less complicated (cheaper) to manufacture...

 

Good thread.

Mac

 

It makes a good story to get one or the other. But the truth is most transmissions have both. Straight cut in the strength areas and helical elsewhere.

I saw a blow up of the SE 6 speed and that thing is all straight cut gears

Here is the 06 Dyna. Straight in 1 and 5th.






Lee

 

Now thats a great explination .Even I understand it now.

 

Helical gears can be made to be just as strong as strait cut gears, but it is very costly. My ship a DDG(guided misile destroyer) uses a main reduction gear that has all helical cut gears. we have 2 LM-2500 gas turbine motors for each reduction gear that generates 50,000 hp per shaft, so the reduction gear is under some heavy load. but as i stated before they are pricey. infact so expensive that the Navy doesnt own them, they lease them form GE for the life of the ship.

Chris

 

So with all that said---why do we still "clunk" while shifting gears?