Precision - Shaft or Rail?

[swisspnp]

Question for all you pro CNC builders.

I am building a CNC to do pick and place of circuit board components, however I've come up blank when choosing between shaft and rail systems.

Does one offer more precision than the other? I'd assume not otherwise one would always be used over the other? Or does one cost more?

I'm looking to find out which system you would use for the highest accuracy possible from a homebrew machine.

And do I need two sets of each in on each side of the axis? Or will just one suffice?

Many Thanks!

Edit: Perhaps its worth mentioning I will also want to mill aluminium on this machine..!

[RICHARD ZASTROW]

Roller rails (more expensive) will produce better accuracy and rigidity. Round shafting (less expensive) lower rigidity.

Dick Z

[swisspnp]

ah ha! So if I can afford the linear rails I shall get those.

Thank you.

Quick question:

When using rails, should I use two on both axis, like in pairs?

eg:
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|| ||
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[RICHARD ZASTROW]

The pairs configuration is what is normally employed. Occasionally a very wide rail with a long bearing slide is possible.

Dick Z