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Wear in linear guides

Wear in linear guides
July 18, 2016 10:01AM
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...


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VDX
Re: Wear in linear guides
July 18, 2016 10:46AM
... sometimes it's the ambient dust source - superfine sand is a killer eye rolling smiley


Viktor
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Call for the project "garbage-free seas" - [reprap.org]
Re: Wear in linear guides
July 18, 2016 10:50AM
I agree, sand is awful, but what gets damaged?


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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: Wear in linear guides
July 18, 2016 10:52AM
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VDX
... sometimes it's the ambient dust source - superfine sand is a killer eye rolling smiley

If you are worried about fine dust you could go with a polymer guide like these from igus: Link
Re: Wear in linear guides
July 18, 2016 10:55AM
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the_digital_dentist
I agree, sand is awful, but what gets damaged?

I think that it would depend more on the type of damage and the way it happened, but I have no idea what would go wrong first.
VDX
Re: Wear in linear guides
July 18, 2016 11:55AM
... the damage depends on material pairings - two similar hard materials are the worst case.

I live in Germany, so not this much sand or dust around ... but sometimes wind from the south brings sand from the Sahara desert to us -- then the cars are covered with fine, highly abrasive dust ... you can see this by the wiper-traces, 'carved' into the glass. And if this dust cames into your workshop, then bearings wear will increase dramatically too!

But my basement is good isolated against dust form outside, so no problems in this direction - more with ambient humidity and rust on steel and iron surfaces.


Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org]
Call for the project "garbage-free seas" - [reprap.org]
Re: Wear in linear guides
July 18, 2016 01:22PM
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the_digital_dentist
but what gets damaged?

It depends... There doesn't seem to be a simple answer. This abstract from an academic paper (unfortunately behind a paywall) gives some idea of the complexity:

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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.

From Slocum's FUNdaMENTALs of Design:

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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.
Re: Wear in linear guides
July 18, 2016 09:15PM
Quote
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...
Most bearing failures I've seen, be it linear or round start with the balls or rolling element. A ball skids, and flat spots start to form. From there it's pretty quick downhill.
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