Wear in linear guides

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VDX
... sometimes it's the ambient dust source - superfine sand is a killer

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the_digital_dentist
I agree, sand is awful, but what gets damaged?

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the_digital_dentist
but what gets damaged?

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On Competing Failure Modes in Rolling Contact
Rolling contact failures are classified according to their failure mode as (a) wear, (b) plastic flow, (c) fatigue, and (d) bulk failures, with the last class arising outside the immediate contact area. The wear failures are subdivided into mild wear by loose particle removal and smearing involving metal transfer. Plastic failures may arise due to overload or to temperature imbalance. Fatigue is of the spalling or the surface distress type. An analysis of the stress conditions in a rolling contact is sketched; the stepwise refinements of the contact model are considered, starting from Hertz theory, and progressively including surface traction, plasticity, elastohydrodynamic lubricant films, surface microtopography, and the inhomogeneities of real metals. Each failure mode is associated with the relevant severity parameters of the contact stress condition, and a description of its mode of formation is given. Guidelines are provided for the identification of that failure mode which, among competing modes, is most likely to render a rolling contact inoperative in a given operating environment.

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FUNdaMENTALS of Design
Most bearings run without any sign of trouble, and then fail rapidly. How can this be so? Bearings are surprisingly robust, but when the lubrication fails, e.g., it leaks out, or a larger particle breaks free, the principle of self-hurt seems to take over: One particle breaks off another, and the two together break off two more... until the particles are like the sands of the sea and the machine comes to a screeching halt. Before failure, however, the machine may start to give subtle warning signs such as an increase in temperature, or increased vibration and sound, or the obvious puddle of oil on the floor.

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the_digital_dentist
Question for the experts: when a linear guide wears out, what goes bad? Is it the rail, the races in the bearing block, the balls, or a combo?

My experience cutting rails with a chop saw and abrasive wheel tell me it isn't likely to be the rails...