Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here


broken shaft

broken shaft

broken shaft

I have a 15mmø shaft that sheared off at a roll-pin hole. The shaft is connected to the input drive with a shear-bolt that did not bread or even bend. In looking at the fractured edge there is a definite difference in the appearance of the two sides of the hole. It also looks like the metal yielded and twisted at the fracture based on the taper in the hole on both ends. Any thoughts on why this shaft would fail and not the shear bolt?

RE: broken shaft

The shaft material was weaker in torsional shear strength in comparison to the shear pin material.

RE: broken shaft

That is a very sloppy hole, lots of wobble room that shouldn't be there.
The shaft was too week from the hole.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: broken shaft

Do you know what material the shaft was made from? Pin manufacturers recommend a shaft diameter/hole diameter ratio greater than about 2.5. It looks like you have that so I'm guessing the material was not very strong.

RE: broken shaft

Background. I am a structural engineer but don't deal with metallurgy. It has been many years since my college Strength of Materials labs but the fracture surface looks odd.
This is the input shaft for a Lippert RV slide gear and the hole is for a roll pin that keeps the shaft centered. This is for my motorhome and is the second gear box that has failed in two years.

RE: broken shaft

Tough to tell if the fracture surface is unusual given the lighting of your pictures, but it looks like a lot of contact between mating surfaces (common in fatigue propagation of this type), and ratchet marks seem to suggest OD-initiated fatigue. You should contact the manufacturer and send it back - I'm sure they they want to know about the problem and will address failure analysis and any make-good you are owed.

RE: broken shaft


RE: broken shaft

I am suspicious of the quality of the shaft and accuracy of the fit.
You can tell that the pin was 'wallowing' because the sides of the hole are flared.
That indicates to me that there was some slop in the system to begin with.
If the pin was only for location then what is the load on it?
The shaft may be under sized or under strength for the job.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: broken shaft

Lippert makes a huge array of mechanical parts for RVs of all sizes.
Their stuff appears properly engineered, to a weight and especially to a price.
Their customers, RV manufacturers, all of them, appear to not be at all reluctant to misapply Lippert's, or anyone's, products, e.g., by using a part that's really one size too small for any particular application.

When you talk to Lippert and the RV manufacturer, I suspect you will find them pointing fingers at each other, which seems to be SOP for both parties, neither of whom will accept responsibility for anything.

I hope that I'm wrong in your case, and someone will step up and do something for you.

Mike Halloran
Pembroke Pines, FL, USA

RE: broken shaft

It is very common in situations like these for the manufactures involved to perform a proper failure investigation. It is not about finger pointing - if there is a problem, then they want to identify it and take appropriate corrective actions before having a large number of failures and warranty claims. Getting a reputation for shoddy parts goes against their business. These types of failure investigations are common and I see them all the time.

RE: broken shaft

I contacted the manufacture and they are sending a new part and want my old one for investigation. Thanks for the help.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close