[Goemon]

I have bought a number of sets of rails and they all feel different. Some have arrived covered in oil and with bearing blocks that will move (and fall off) unaided if you just tip the rails. Others feel fairly stiff and the blocks only move if you push them, even if you apply lots of oil. Which is correct?

Should I even be concerned with how the bearings feel and how easily they move (as long as they can move up and down the rail without issues)?

[ger21]

Depends on the preload, and how clean they are.
Bearings with a heavy preload can feel "Stiff", and not smooth, until a bit of force is applied.
Light or no preload will slide right off.

And if they have old, thick grease in them, that can also affect the motion.

Don't confuse moving freely with being loose. They should never be loose.

[Goemon]

Depends on the preload, and how clean they are.
Bearings with a heavy preload can feel "Stiff", and not smooth, until a bit of force is applied.
Light or no preload will slide right off.

And if they have old, thick grease in them, that can also affect the motion.

Don't confuse moving freely with being loose. They should never be loose.

When I say "loose", I am only referring to how easily the blocks slide up and down the rail. I don't mean you can twist the blocks or any other type of play.

Is the preload on these things usually adjustable or is it a fixed value you can look up in the specs?

Also, what do you use to lube your rails and blocks. Someone else here recommended White lithium grease but, after trying it, I think they were wrong....

[ger21]

No, Preload is not adjustable. Most name brand bearings will usually be available in 3-5 different preloads.

For grease, at work, we use Kluber GL-261, but it's very expensive.
Mobilux EP1 is similar, much cheaper, and easy to get. https://www.amazon.com/Mobilux-EP-Gr...ds=mobilux+ep1

[Goemon]

No, Preload is not adjustable. Most name brand bearings will usually be available in 3-5 different preloads.

For grease, at work, we use Kluber GL-261, but it's very expensive.
Mobilux EP1 is similar, much cheaper, and easy to get. https://www.amazon.com/Mobilux-EP-Gr...ds=mobilux+ep1

Thanks, I just ordered some mobilux.

I probably should have asked this before I bought my rails but.... how important are preloads? I.e. For what reason do they offer a selection of different preloads and what makes one choice right for an application and another wrong?

I don't know if there is any correlation but it seems like the bearing blocks (that I own) that feel tightest are the larger ones with larger ball bearings in the cage. My smallest rails are the ones that I could move by tipping the rails. Does this indicate that preload should be specified based on the weight of what is being moved?

I was mainly looking at the specs for how much weight and / or force each size of rail could handle in the orientation I planned to use them.

[ger21]

https://www.linearmotiontips.com/how...guide-preload/

[Goemon]

https://www.linearmotiontips.com/how...guide-preload/

Thanks. It clearly explains the factors that are effected by preload although I can't see how your average diy builder here would be able to specify their needs. It sounds like one of those things where I'll only find out if I needed more or less if there is a problem....

The good news is that, if there is a problem with speed or deflection, I'll have more ideas on how to fix it after reading that.