Crown on an external spline 2

[borjame]

Hello everyone,
I'm trying to design a crown on an external spline in an attmept to distribute the load over the length on the spline. Initial FEA shows the bulk of the load is taken up at the start of the spline so I'm trying to redistribute the load for lower stresses and more life.

Is a crown even appropriate? The little information I've been able to find talks more about misalignment, but I was told a crown could solve this problem.

If it is appropriate, what are the guideline with regards to how the crown is laid down, should it start at the spline start and taper to the other end of the spline, should it max in the middle and taper to either end?

I've never worked with gears before so excuse my ignorance if my terminology is confusing. Any help or guidance you can provide is appreciated!

 

[digger200]

I think a true crown only works if the load is central. With a spline the bar twists, so using a slight helix may be better but then you have an assembly problem.

 

[Matt51]

"When Splines Need Stress Control" by Darle Dudley
Reprinted in Gear Design and Application by Nicholas Chironis. A crown can be partial or full. Works very well. There are limits to how much misalignment a spline can handle.

 

[tbuelna]

borjame,

Crowned (external) splines are used quite commonly. They are beneficial where shaft misalignment may occur due to assembly tolerances, thermal distortions or distortions under load. The crown helps to "centralize" the contact along the spline's length.

The downside of crowning a spline is that it's load carrying capacity is reduced. So generally, if you crown a spline it must increase in diameter for a given load.

Sometimes, shafts with crowned splines are intentionally installed with a small degree of angular misalignment. This results in the spline interface having a wiping motion as it rotates, helping to create a more favorable lube condition at the contact area.

 

[tbuelna]

borjame,

digger200 is also correct. If you are very clever with your spline design, you can manufacture it with a controlled amount of lead so that under load it has uniform contact along it's length. But this is usually very difficult to get right.

As a rule of thumb, the L/D of your spline should be kept low and should never exceed 1.0.