×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

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

Related Articles

Jobs

Tapped holes and fatigue

Tapped holes and fatigue

Tapped holes and fatigue

(OP)
I am currently designing a system that requires an actuator to be fastened to a horizontal baseplate via a clevis plate. During operation, the actuator will transmit cyclic loading to the baseplate (normal to baseplate) with a high force. After a significant number of cycles, the actuator and clevis plate will be replaced but the intention is to keep using the baseplate.

My question is: can I use tapped holes in the baseplate, i.e. can tapped holes be re-used for an application where fatigue failure is a risk? (the baseplate itself is designed such that it is below the endurance limit). Because of space issues I can't get a nut on the underside of the baseplate.

Thanks in advance, KDB

RE: Tapped holes and fatigue

Ask yourself this: is the thread actually seeing a reversing load?

RE: Tapped holes and fatigue

(OP)
Not directly axially - however the top of the plate is alternating between tension & compression - I don't know if this would cause an issue in the surface with the tapped holes?

Also, I don't know what the cumulative effects on the thread are when re-using the hole for this kind of application

RE: Tapped holes and fatigue

Based on what I'm imagining (**) your arrangement looks like, I'd say if the bolt clamping force is "high enough", the friction between the clevis plate and baseplate will easily resist all anticipated and unanticipated transverse forces, and the bolts and threaded holes will be subjected to negligible alternating forces. The bolts also will never loosen in service, so "locking devices" should be used only for bolt retention, just in case, if at all.

(**) http://www.newtonsapple.org.uk/wp-content/uploads/...

RE: Tapped holes and fatigue

Hi KDB 17

No reason why you can't use tapped holes rather then nuts, however depending on the material the tapped holes are in you would need to check the shear stress for that material and compare it with that of the nut mterial.
I the preload is high enough on the bolt then the cyclic stress in the fixings should be quite small, it is interesting to note that when you tighten on a female thread whether it's a nut or tapped hole the stress is actually compressive unlike the bolt which is in tension.

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

RE: Tapped holes and fatigue

(OP)
Thanks for your replies Tmoose & desertfox

RE: Tapped holes and fatigue

Can you add two (or four) pins (dowels or press-in rolled pins) to take the changing (sideways) shear forces? That way the clevis assembly is held "down" (clamped to the baseplate) by the tapped holes (always compression forces) but the pins take the changing sideways forces.

RE: Tapped holes and fatigue

The combustion and inertial forces (hundreds or thousands of pounds) applied to a typical non-opposed auto engine main bearing cap are mighty significant and highly alternating, primarily in one plane.

Two bolts per cap proved sufficient for a bunch of years.
http://blog.ecklerscorvette.com/wp-content/uploads...

The cap sits snugly in a shallow register in the engine block, but that is to maintain accuracy of the machined hole ( 0.0005" or less ) thruout repeated disassemblies, not to resist the considerable forces in operation.

Bolt clamping forces, for decades controlled by installation tOrQuE, applied to decently machined faying surfaces created friction and was dead reliable.

RE: Tapped holes and fatigue

I'd be more worried about wear on the flanks of the threads. Use a lubricant if you aren't already.

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!


Resources


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