×
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

Linear Bearing Question

Linear Bearing Question

Linear Bearing Question

(OP)
I am wanting to have a rectangular base plate move on two parallel linear rails.  The base plate will have a linear bearing in each corner.  The plate will be driven from the center.

My question: Is there a common (rule-of thumb)ratio of the width Vs. length for a bearing arrangment like this?

I am concerned that if the bearings are too close together and the distant between the rails is excessive, the base plate will tend to "Bind" and not move freely.

Thanks

RE: Linear Bearing Question

You may wish to allow the bearings on one end of the plate to float in the direction toward the other bearings.  This will reduce the fabrication accuracy required in the assembly.  As far as a rule-of-thumb goes, I'm not aware of one.  I suggest in addition to the above suggestion you consider the rigidity of the rails and bearings under the expeced load conditions and make a judgement call.  If your bearings are roller or ball bearings the reduced friction will help a lot.  

RE: Linear Bearing Question

(OP)
Stroker,
The bearings will not be allowed to float, but rather be fixed by a shoulder to increase the rigidity of the system.  The rails/bearings will handle the loads just fine.

Thanks

RE: Linear Bearing Question

Take a look at machine tool way construction for an example.   One common design uses a vee way on one side for alignment and support and a flat way on the other for support only.  Of course this is not the only method, just one successful example.  Providing redundant constraints as you propose may be more rigid but will almost certainly be more difficult to produce.  

RE: Linear Bearing Question

   Generally I dictate the distance of the bearings by the load.

   If the system is bearing the load vertically thru the rails than the only load left that would cause binding would be that of the force need to move the load. Most manufactures list this load capability in there catalog. With out seeing any numbers I suspect that your design is fine and will not bind considering...

a) Its fairly dificult to make one runner block bind by applying torsional force. (Note it's really easy to lock em up if your rails aren't running parrellel)
2)By having two runner blocks on the same rail you have effectively spread any load across that distance (Most MFG's of runner block rail systems can get you all of the formulas for calculating loads for their runner blocks. I had a neat few pages that gave all of this info but can't seem to locate it presently )
3) Assuming your load is centered on the runnerblocks and your pushing in the center of the load, your torsional load should be little or nothing.

I guess that's as close as I could come to a rule of thumb. Although I've seen a number of bushing style plates lockup due to binding of this sort, I've yet to see a runner block and rail lock up under these conditions, wear prematurely, yes, lockup no.

~Matt         

RE: Linear Bearing Question

Check out www.pacific-bearing.com .  I used their bearings and shafting to move an Induction welder to from the weld box on a tube mill.  My guess is the welder weights around a ton - ton &1/2.

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