[Beowulf] Re: What is the right lubricant for computer rack sliding rails?

Gus Correa gus at ldeo.columbia.edu
Fri Feb 6 11:10:48 EST 2009


Dear Beowulfers

Thanks for the answers so far.
It has been an exciting and lively debate!
Given the number and variety of suggestions,
technical and well humored,
I presume the subject is of general interest,
and others may have experienced similar problems with their
own rails and lubricants.
It is amazing how much expert advice one can get from this list,
even for such a mundane question!

Here are my explanations to answer Bob Drzyzgula's question,
and RGB's insightful speculations on the nature of the rails.

I am talking about telescoping rails, metal on metal,
no ball-bearing mechanism,
which I think match Bob Drzyzgula description.

Currently I have a problem with a "three stage" telescoping
rail, of wide profile, manufacturer ... doesn't matter.
The pair of rails is brand new, I installed it properly,
as far as I can tell.
(They come with awful one-page instructions, with diagrams
that belong to other rail models, but we got used to this
type of thing.)

Visual inspection of the rails didn't show any signs of
them being warped or twisted.
With no load, they work properly.
The rails support a heavy 5U RAID file server.
When loaded, sliding is not smooth.
The telescoping stages don't always move symmetrically,
or as expected (e.g. the inner stage may come
out after the middle stage, etc).

I saw similar problems before,
mostly with telescoping rails on bulky multi-U
RAID servers and heavy rackmount UPSs.
Mind you, I didn't assemble all of those rails.
And to date, I have never used any lubricant on them.
But in the case at hand, I can see no alternative to
a proper lubricant.

Less often, even the higher quality ball-bearing rails that
support 2U nodes may get a bit hard to move.
However, this may be less of a rail problem than
caused by small asymmetries on the rack mounting holes, I suppose,
as the bottom and top of a node chassis drag along the neighbor
chassis.

The particular rack I am using is old,
salvaged not from the armed forces,
but from our oceanographic equipment of our old decommissioned ship.
Although the rack is in good shape, it may have larger asymmetries
on the mounting holes than modern racks do.

Anyway, it's been a lovely and instructive debate, I must say.
Please, advise!

Many thanks,
Gus Correa
---------------------------------------------------------------------
Gustavo Correa
Lamont-Doherty Earth Observatory - Columbia University
Palisades, NY, 10964-8000 - USA
---------------------------------------------------------------------


Bob Drzyzgula wrote:
> One thing that Gus didn't explain to us was what sort of
> rails he's talking about. If they are ball-bearing slides,
> or even the kind with small wheels, it is actually kind of
> surprising that they would need any lubrication at all. Is
> it possible that these are just metal-on-metal telescoping
> slides without any sort of sophisticated bearing system? I
> know those can get pretty sticky. In any event I'll
> join those who say a light application of some sort of
> non-volatile grease would be best. Among other issues,
> any oil or aerosol is too likely to get into the general
> environment and on other surfaces in the vicinity of the
> rack, and will likely will not do well after long periods
> of disuse at the modertately warm temperatures and high
> airflow of a machine rack.
> 
> I will also especially join those who argue against
> WD-40. To the extent that it acts as a lubricant, this is
> almost a side effect. I think that it used to be that they
> wouldn't even call it a lubricant -- the word certainly
> didn't used to be listed on the can -- but I see from
> their website that they do now use the word "lubricates",
> in number 4 (out of 5) on the list of things that it can
> be used for.  The downsides -- especially its volatility
> -- pretty well outweigh its advantages for something
> like this.
> 
> --Bob
> 
> On 05/02/09 11:49 -0500, Gus Correa wrote:
>> Dear Beowulfers
>>
>> A mundane question:
>>
>> What is the right lubricant for computer rack sliding rails?
>> Silicone, paraffin, graphite, WD-40, machine oil, grease, other?
>>
>> Thank you,
>> Gus Correa
>> ---------------------------------------------------------------------
>> Gustavo Correa
>> Lamont-Doherty Earth Observatory - Columbia University
>> Palisades, NY, 10964-8000 - USA
>> ---------------------------------------------------------------------
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