Linear rail smoothness

[Putrgeek]

I have read that linear rails should not be so smooth that they fall freely from top to bottom on the Z axis “fast”.  I have read that they should require assistance to move. 

All of my Z axis rails fall freely when raised. i have not oiled them and they are “fast”. 

Is this a bad thing?  If so, how do you “slow” down a rail. 

They are Vivedino and they came with my Formbot kit. 

Thank you for any info this great community can provide. 

[SteveThatcher]

I would be curious who is saying that linear rails should not be smooth. As long as the slider is moving without rocking in place or any movement other than up and down a rail. The positioning of the slider is by belt in the voron and lead screws in CNC machine applications. Maybe I missed something, but a linear rail in my view should be free moving with the conditions I already stated. Point me at some technical document that explains why they should not be smooth.

[Simon2.4]

Just now, SteveThatcher said:

I would be curious who is saying that linear rails should not be smooth. As long as the slider is moving without rocking in place or any movement other than up and down a rail. The positioning of the slider is by belt in the voron and lead screws in CNC machine applications. Maybe I missed something, but a linear rail in my view should be free moving with the conditions I already stated. Point me at some technical document that explains why they should not be smooth.

lubricant viscosity fills gaps and reduce backlash. this lubricant film fills the microscopic features but adds resistance to movement. The key to good lubrication of metal is balancing film strength and mechanical resistance. If you are looking for a whitepaper or something google it yourself but its pretty common knowledge in engineering. So yes, a properly lubricated rail will have some light resistance to movement as the flowing lubricant wastes a bit of energy.

[Simon2.4]

30 minutes ago, Putrgeek said:

how do you “slow” down a rail. 

you don't, just lubricate as indicated by the manufacturer or as instructed by one of the 'gurus' like nero3d on youtube

[SteveThatcher]

1 hour ago, Simon2.4 said:

lubricant viscosity fills gaps and reduce backlash. this lubricant film fills the microscopic features but adds resistance to movement. The key to good lubrication of metal is balancing film strength and mechanical resistance. If you are looking for a whitepaper or something google it yourself but its pretty common knowledge in engineering. So yes, a properly lubricated rail will have some light resistance to movement as the flowing lubricant wastes a bit of energy.

understand. I guess the original question had me thinking much more resistance to moving. I have used linear bearings for years and guess I never asked the same question...