29 Dec
2002
29 Dec
'02
10:44 p.m.
On Dec 29, 22:06, R. D. Davis wrote:
While thinking about racks to use for mounting my
PDP-11/44
components, as well as other equipment from test equipment to audio
and synth equipment, something just occured to me: why bother with
hunting down steel racks when some 2x4s and lag bolts may suffice just
as well? I was thinking that one can just run 2x4s from the basement
floor up to the heavy wooden rafters, attach them to the rafters, and
then add horizontal supports at the bottom to space the vertical 2x4s
apart properly. Any thoughts on this? I guess the museum-type
equipment purists won't like the idea, but it would be a cheap and
functional solution for many of us. :-) Has anyone else here tried
this?
Not exactly this, but in addition to (and adjacent to) my racks, I have
some adjustable shelving which uses cantilever brackets, fitted to upright
rails that are screwed to the 2"x4" vertical "studs" in the wall.
The
brackets are 610mm (about 24") long and so the shelves are 750mm (~30")
deep. The brackets and rails are Spur "Steel-Lok" type and each pair of
brackets is rated to hold 75kg (175lb). I tested their security by
climbing up them before I entrusted my precious computers and VR14 to them,
so I'm sure a 2x4 frame will hold any reasonable amount of rackmount
equipment *providing* you have appropriate fixings.
http://www.spurshelving.com/html/tech/steel.htm will show you the stuff I
used, I'm sure there's something similar in the States. I used a baby
version of the same stuff for shelves on a couple of steel-framed trolleys.
HOWEVER, the real utility of a rack is that you can mount things on rails
and slide them out whilst they're still connected; and that you can adjust
the position of things as more interesting equipment comes along (thanks,
James! [1]).
In fact, it's very hard to work on some things unless you can slide them
out part-way, like my PDP-8/E (which is slightly poorly ATM, but that's
another story) or most of my PDP-11s.
More than that, it's practically impossible to *use* certain things unless
you can slide them out -- you need to slide an RL01/RL02 halfway out of the
rack to change the disk pack, for example. Those b***s are heavy, and you
really do want to use the proper rails. With the ball-bearing rails,
changing an RL02 pack is an operation you can do without thinking about it;
without, it becomes a "put it off until next week" job.
The first catch is that rails and other (static) rackmount equipment are
intended to fit precisely-spaced holes. Despite what some people think,
they're neither random nor equally spaced (forgive me if you know this).
They're in groups of three with one hole in the centre and one each 5/8"
above and below, leaving 1/4" between the centre of the upper (or lower)
hole and the start of the next U. In other words, the spacing goes 5/8",
5/8", 1/2", 5/8", 5/8", 1/2", ... and 1 rack unit (1U) is
1_3/4".
American-style racks (RETMA?) use round holes, sized to be a good clearance
for No.10 machine screws (or M5 m/screws) and are used with Tinnerman nuts.
European racks use square holes, to which you fit cage nuts (usually M6
but sometimes M5), and the centre hole of each 1U group has, by convention,
a little notch at the side, so it's easy to see where the centre of each 1U
space is.
For that reason alone, it would be much easier to buy the upright flanges
which have the holes pre-punched in the right places. They look like
overgrown Dexion angle, or steel angle with a lot of holes (front face) and
slots (side, for mounting to the uprights). You can get them here in sizes
from 3U to 48U (common sizes are 3U, 6U, 12U, 18U, 32U,
42U, 48U). Price
depends on quality (ie, strength) but they're not expensive.
I bought a
24U strip and cut it up for my "hub of the universe" wiring rack. That's a
14" deep 6U high frame with sides of 1" square steel tube and flat-strip
cross members at the back, mounted over the workshop door. It holds my
main Ethernet switch, and several patch panels for UTP, coax, and fibre.
Another reason to buy the proper uprights is that some rails, notably those
for an RX02, PDP-8/E, and various other devices, fit to the back surface of
the flange, not the front (as most "static" equipment does). If your
wooden uprights are the right distance apart to directly fit the sort of
equipment that has mounting "ears", ie screwing the ears straight into the
front of the wood, you'll never be able to fit most types of slide rails,
unless you do a bit of woodwork to provide a rebate. Ditto for most
shelves, both static and sliding, except cantilever shelves (which fit from
the front surface only, but cost more than ordinary ones).
Lastly, has anyone on this list tried retrofitting
non-rack-mount
equipment into racks? E.g., welding (or "JB Weld"ing) rack-mount tabs
onto systems like PCs and Kaypros, as well as making rack-mountable
shelves to hold the Macintoshes, etc.?
Rackmount shelves are good for that -- just make sure you have enough, or
you end up with systems on top of each other again. Cantilever shelves are
particularly good because you can always get at the mounting screws, which
are only on the front. Conventional shelves are much cheaper but you need
to be able to get your hand and screwdriver into the gap between the
shelves to reach the screws on the underside of the shelf you're moving --
oh, and BTW they screw into the sides, which will be a little awkward with
big woodscrews.
We use lots of rackmount shelves at work, for PCs (mostly running Linux)
and Sparcs that weren't designed to rackmount.
Otherwise, just screw a bracket onto each side of the case. The screws
needn't be very large, as most of the forces are in shear. Self-tapping
screws will do for most metal cases, machine screws with washers and nuts
on the inside for plastic. I wouldn't weld things. Cases are thin,
usually zinc plated (nasty fumes), and hard to weld. I certainly wouldn't
use epoxy or anything like that. If you ever want to remove the brackets,
two or three small holes in each side is much better than the mess a broken
weld or epoxy will leave.
A few other thoughts:
As someone else pointed out, having the side panels makes a big difference
to the sound level. It might also make a big difference to the airflow,
though, which is why proper racks have fans of their own, normally in the
top :-)
It's obvious that the width between the uprights is important, but just in
case you're wondering, the depth is not (much). A lot of things are
front-fixing-only, and most rails are adjustable. Anyway, most flanges
have slots rather than holes for mounting, so some adjustment is possible.
I can only think of two items where the exact depth matters: my SGI
Origin 2000 (which has two slightly superfluous brackets at the back), and
an RL01/2 drive, where the shipping bracket is supposed to be fitted to the
rear flange (which therefore has to be a particular distance from the front
flange). Nevertheless, there are standard depths, like 600mm, 800mm, and
950mm (in Europe) but they're more a matter of convenience. FYI, a
standard DEC rack measures exactly 25" from front surface of front flange
to back surface of back flange.
To be honest, I think you'd be better off finding a secondhand rack. It
will already have all the right holes, possibly the side panels, and if it
has casters, it might be more versatile than a fixed frame. Providing the
casters are strong enough to take the total weight (ie not intended to be
supplemented or replaced by jacking-screw feet) it's useful to be able to
move a rack a small amount from time to time. Don't forget you need access
to the back as well as the front!
[1] James is a list member who has occasionally helped me shuffle a
PDP-11/40 up and down a rack. No need to remove the power supply if he's
around :-)
--
Pete Peter Turnbull
Network Manager
University of York