Timing shaft Stress concentration

[Garrett Green]

I am being asked to approve something but I have no way to verify through calculations so I am hoping someone with more experience can tell me if this is a bad idea.

Essentially we have a timing shaft that we through drill and use a spring pin to attach a coupling. the through hole was drilled off center so they want to rotate the shaft 90° and drill a new hole so we can still use the shaft.

I have looked into stress concentration and I found Kfs to be 2.52 for the original hole, but I can not find a way to calculate the stress concentration for a second hole (probably because there is no reason to do it). Even if I could calculate this unfortunately I can not calculate life of the rod using any failure theories because the moment on the rod will depend on how much weight the customer puts on this along with how well it is built and how much friction it sees. My thinking is, if I could calculate the stress concentration added by drilling a second hole it would give me an idea how much it will weaken the shaft so I can make a more educated guess.

More parameters:
diameter of rod = 0.625"
rod material = 1018 CD Steel
Sut = 63800psi
hole diameter = 0.1875"
hole distance from the end of shaft = 0.5"
There should be no bending stress, it should be purely rotational. I can elaborate on why if you need to know.

This image should help:

If my idea for stress concentration seems like the right approach does anyone know how to calculate this? if not, does anyone have a better starting point for me?

Thank you!

 

[dvd]

Don't know quantities, but buying a new piece of shafting may cost less than the time to correspond on Eng-Tips and then provide calculations.

What mounts on opposite end from through hole? Can you flip the shaft 180 degrees and drill the opposite end?

 

[desertfox]

Hi Garett Green

I’m with dvd on this one in that it might be easier to provide a new shaft, one other possibility is could the shaft be turned around and if so would the hole that’s drilled wrong still be in a stress environment?

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[Garrett Green]

Sorry for the delayed response. Had something come up last week and I couldn't come to work. Unfortunately we can not flip the rods because a gear is already welded onto the other end. Thank you both for your input. Unfortunately it was quite a few of the shafts that were drilled off center so they do not want to scrap them. They have found a different solution that they are happy with for these improperly drilled shafts though.

Thank you both for your time!