[Beowulf] flange clearance on sliding rails

David Mathog mathog at mendel.bio.caltech.edu
Thu Oct 20 09:52:52 PDT 2005

Jim Lux wrote:

> The fixed part has a right angle at the end which is supposed
> to mount to 
> the vertical rails. It mounts on the INSIDE of the rail (i.e. from the 
> front of the rack, the fixed part is entirely behind the plane of the 
> vertical rails.

That was quite helpful, thanks.

I'm trying to put this particular set of rails into the
rack with the square holes.  To mount the fixed part on the 
inside of the rails I have to pop off the caged nuts
that normally live on the inside of the mounting surface of
the rack (oriented in the XZ plane.)  After removing the nut
a screw from the front can go through the square
holes on the rack and through the slots on the fixed part's mounting
flange.  Unfortunately the supplied screws have heads which will
then pass completely through the square hole.  There seem
to be two options:

1.  Mount the caged nuts on the front of vertical rail and
put the screws in with the heads in the +y direction and
the tails (is that the right term for the threaded part?)
in the -y direction.  Advantage: no
extra hardware needed.  Disadvantage:  caged nut and 
screw tail extending through said caged nut will extend in the
-y direction and require much longer mounting screws for the
flange on the server itself, which will be oriented in the
opposite direction; extremely difficult to reach screw head
to attach fixed part of rail system.

2.  Obtain washers large enough to cover the square hole
and put the screws in with the heads in the +y direction and
tails in the -y direction, with nuts on the inside of the fixed
part's mounting flange.  Advantages:  somewhat less interference
with the node's mounting flange than; much easier to
turn the screws, and the interior nuts can be placed blindly
by holding them with one finger until the lock washer tightens
up.  (1).  Disadvantage:  have to buy some washers and lock washers.

In this same rack we have a UPS mounted that came with odd
conical washers.  The UPS sits in a sort of tray that is attached
as in (2) above.  The odd conical washers allowed the mounting
screws to partially recess into the square holes.   That seemed
like a pretty good solution to me, but I don't recall having ever
seen that type of washer before, so finding some more may not
be so easy.

Is there some other standard way (3?) for mounting the fixed
part of the sliding rails on racks with square holes?  Perhaps
somebody makes a square recessed washer specifically for
putting screws in from the front?  That is, this washer would

A: a center hole for the screw to pass through.
B: a circular flat area larger than the hole to retain
  the screw head.
C: a square area outside the circular area to fit in the rack's
  square hole.
D: a flange outside and above the square area (in the -y direction)
  to clamp onto the front of the rack, to prevent said washer
  from being pulled through said rack's square hole when tightened.

Hmm, I suppose one could obtains something similar to this by bending
open the caged nut, removing the nut, and replacing it with the screw.
Unclear if the resulting structure would be very strong though.


David Mathog
mathog at caltech.edu
Manager, Sequence Analysis Facility, Biology Division, Caltech

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