Linear Guideway question

[karthur]

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

 

[Hippo41]

I'm not aware of any 'rule of theumb' to set the plate size, but the stiffness of the plate, and therefore the it's deflection under load is of extreme importance - linear bearings can only handle limited deflections.

If you are using round linear shafting, you have to choose between end supports (i.e. the shaft is like a bridge) or fully supported rail (like a train track) that is far stiffer.

So called Linear Way systems (such as IKO Linear Way, Star's Ball rail systems) are far stronger, but also more expensive.

In any case you can add extra bearings along the shaft if you need them.

I would get your local linear bearing experts in who can do the calculations for you - or at least get them to give you a decent catalogue. Essentially decide what suits you and let them propose a bearing system that will accomodate your needs.

If you need Internet Based catalogues, I find the STAR Linear catalogue very useful on

http://www.rexroth-star.com

Lester Milton
Telford, Shropshire, UK

 

[jmoritz]

Rule of thumb 3:1

That is the separation of the rails versus guide to guide on the rail should be 3:1.

OR

The separation of the guide to guide on the rail versus the separation of the rails should be 3:1.

 

[karthur]

Jmoritz,
Thanks for replying. I think you totally understand what I am asking, but I want to make sure I interpret what you are saying. I posted a little picture below.

From what you said, the "Y" dimension should be 3 times the "X" dimension. Correct?

 

[jmoritz]

YUP!

Or vice versa....helps to eliminate moment loading on the blocks and therefore binding.

 

[unclesyd]

You might want to look at Linear Rotary Ball Bearings

http://www.e-lrb.com

Or one called Rotolin

http://www.brauer.co.uk/bearings/linear.html