[JukeBox]

I wonder why people almost allways protect ball screws on their CNC routers while they don't protect rails. Ball nuts have wipers just like linear bearings/blocks. Why is it more important to protect ball screws than rails? I am not referring to hobby routers only. Just look at: Haas GR510, CAMasters, ShopSabres and others, they all have rails exposed.

[ger21]

Most routers have ballscrews exposed as well, as it's hard to cover really long ballscrews.

[JukeBox]

How harmful actually is MDF dust for example? Can it penetrate into the round linear bearing despite wipers?

[A_Camera]

How harmful actually is MDF dust for example? Can it penetrate into the round linear bearing despite wipers?

I agree, if you are milling MDF you should protect everything, including your lungs. It is though not easy to protect everything but yes, if one protects the ball screw one should also protect the linear bearings. One reason I can think of why people protect the ball screw more than the slides is that ball screws/nuts are more complicated and more expensive to replace, and also more complicated to clean, if one would decide to remove and clean.

[JukeBox]

That looks promising but I wonder how it works and how sustainable it is in dry environment

[ger21]

How harmful actually is MDF dust for example? Can it penetrate into the round linear bearing despite wipers?

Yes, it will penetrate the bearings. Round bearings are worse, because they don't have grease fittings. Regular greasing will force out the old, dirty grease and dust.
Profile bearings with double shields and scrapers are the best, and run fine in very dusty environments, if they are greased regularly.

Same with Ballscrews. If you grease them regularly, a little MDF dust won't hurt them.

Any good machine design should have good dust collection, and shouldn't allow most chips and dust to settle on the bearings and ballscrew.
Small amounts of dust and chips are OK.
Running ballscrews and rails that are buried in dust will eventually be a problem.