×
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

Jobs

Moment Acting on a Power Screw

Moment Acting on a Power Screw

Moment Acting on a Power Screw

(OP)
Hi,
I have a power screw that closes a scissor like mechanism. The tapped portion which acts as the nut inflicts an axial force against the motion of the screw, however, the force originates below the axis of the screw, therby creating a moment at the center of the screw. I have been running the equations for calculating the required torque to move the load axially, but I am unsure how to account for this moment on both the nut and screw threads. It seems clear that this moment has an impact on the required torque but for the life of me I cant clearly see how to account for it. Maybe I've had too much coffee.  Any help or guidance would be appreciated! Thanks!

RE: Moment Acting on a Power Screw

I suppose if I wanted to figure it out on paper I would start with the chapter from something like Shigely, Spotts or Bickford that discusses where the torque goes when you tighten an ordinary nut and bolt.  Your situation would seem to be simply a minor modification to that calculation, after you resolve the moment into a couple on opposing sides of the nut.

I don't have access to my copies at the moment, and am not sufficiently motivated to derrive the equations on my own.

It would seem far simpler to run a quick test, which would more accurately capture the specifics of your application.

RE: Moment Acting on a Power Screw

As a quick calculation which will be quite accurate I will resolve the moment into a couple of opposing forces on the nut/screw thread pitch diameter. Then multiply the some of the forces by the pitch radius and the coefficient of friction. This will give the added moment needed to overcome the moment due to the off axis force.

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