[Rack Stuff]

[James Husted]

Here is the `official` USA rack standards (EIA doc RS-310-C) if anyone is
interested. I've found some racks made that don't quite work with the
standard (the between the rails measurment is usually off). Anyway, here
they are:
For the 19" standard - 19.031"max , 18.312 inches hole row to hole row,
17.72 inches minimum clearance between rails. Holes are 0.281+/-0.005
diameter, or 10-32 Class UNF-2B, 12-24 Class UNC-2B, M5X.8-6H or M6X1-6H
threaded.
There is also but harder to find 24" (24.031,23.321,22.72) and 30"
(30.031,29.312,28.72) standards.
All use standard height panels in what is typically called a U unit (1U 2U
etc) with what is now standard RETMA hole patterns. Sometimes one can run
into the older mostly obsolete Western Electric panel at surplus stores.
Not much difference, just one less hole. The hole spacing on both versions
repeats every 1 3/4 inches. The holes are like this: End of rail - 1/4"-
(1st)hole - 3/8" - hole - 3/8" - hole - 1/2" - (1st) hole - repeat. The WE
panels dont have the middle hole (between the 3/8" jumps).  So this looks
like the panels should be in 1 3/4" increments, but in the standard they
should be 1/32 inch less to allow clearance.  The RETMA (which is now the
industry standard) increments are
1U = 1.719"
2U = 3.469"
3U = 5.219"
4U = 6.969"
5U = 8.719"
etc.
Where the holes end up to allign with the rails is yet another standard, or
standards I should say. Theres the EIA and MIL STD 189.  If you ever
wondered why some 3U panels have the holes at the edges and some towards
the middle set, thats why. Also the use of notches vs. holes - another
variable. I've see a rare panel or two with both holes and notches. Usually
the 5U or larger - notch,hole,hole,notch.
As you can see the industry likes to spec everything. The trouble is many
people dont make to the spec. I've made panels to the 1.75 height and over
the 17.72 wide sizes and have been nailed for it. Some rack rails have a
smaller width and you can get the units in only by taking side screws off.
I have one Mirage that has extrusions for the ears and it bearly fits in
the rack.
There have been  Half-Rack standards proposed (mainly by Rane) but I don't
know if a standard has been excepted by the Electronics Industries Assoc.
or not

-James Husted

James Husted
Art Director, Web Master, Symetrix Inc/Lucid Technology
jhusted at symetrixaudio.com
jhusted at lucidtechnology.com
jhusted at halcyon.com