Questions about rack for rack mounted devices

[Bicurico]

Hi,

I own by now many professional receivers, modulators and encoders, as well as test equipment like the CRTU. All are prepared as 19" rack-mountable devices.

My wife wants me to organize the room where I keep my stuff (its a big open space, meant for general leasure). One of her current objections is that I have all these devices piled on my huge desk with tons of cables. I agree that it is not a pretty sight for non-technical people (I love the sight...). In addition there are 3x 21" TFT monitors, 1x 15" TFT monitor and one 15" Multipurpose TV. Ok, it is too much for an L-shaped desk. She is right and something needs to be done.

So my idea to straighten this up would be to purchase a rack and put all those rack-moundable devices inside.

I do understand that most are 2U, which describes the height in "U"nits... The CRTU is 6U, some are 4U.

I think I need something like a >44U rack. I did not want to put a specific brand in here, so here is a Google Image search instead: https://www.google.pt/search?q=44U+rack&source=lnms&tbm=isch&sa=X

This is what I want to buy. The cheapest new one I found comes at around 500 Euro, I have seen second hand units at around 100 Euro - but either not close to where I am located, or the wrong colour (I want a black rack with glas door), or the wrong depth (I need at least 550mm depth).

And here is the question:

When I look at different racks, I only see the front rails with holes to screw in the front sides of the device.

But how is the rear part of the device mounted?

As an example, lets consider the R&S CRTU: it is pretty heavy and has the rack-mounts on the sides of the front plate. There is no way you can hold the whole CRTU just by these 4 screws!

So what accessories do I need to put everything secure inside a rack? I saw that some come with 1 or 2 plates?

Any additional tips and thoughts on buying a rack?

- I want a glas door, so I can always see my devices. It should be a plain transparent glass, because some devices have screens.
- It needs to be at least 550mm deep, because of the length of some devices. How much should I consider for the cables on the back side?
- I need easy access to the rear - how hard is it normally to remove the back plate of the rack?
- Having the rack on wheels would be great: any consideration required? Do these weels work, or is the whole assemby to heavy?
- Would it be better to have 1x 44U rack or 2x 22U rack?
- I did not consider any thermal issues, but my devices are not used 24/7 nor do I switch them all on at the same time. I think ANY rack will do?

Regards,
Vitor

[fourtytwo42]

There are many different styles of rack!
For heavy units its normal to have front to back shelves or L shaped runners, there is no standard for these so every vendor has there own mounting method. If you are buying 2nd hand make sure you can get the accessories you will need.
Certainly cooling is likely to be a problem if the rack is sealed, some have vents in the back door or underneath for intake and a mushroom top or similar for exhaust with fans being optional.
Rear space beyond the units depends on connector overhand and cable bend radius, don't forget to leave some air space.
Wheels are possible but for a heavy rack it depends if your floor covering can cope!
Another thing to consider is front void (behind the door) depth being suficient for knobs, handles etc on the front of your instruments
Ohh and another gotcha is that 2u may not be 2u by the time supports (shelf/rails) are accounted for.

[madires]

To have enough space for everything I'd go for a 80cm by 80cm rack. Also get a mounting kit (screws, washers and so on), rack-mounted power strips, some cable management and a few shelves. The large rack allows you to mount some stuff (without knobs) at the back side too. Some rack designs let you move the front and back rails which might be needed for having enough space for cables connected to front inputs/outputs.

[TerraHertz]

Rack frames always have same-style mounting rails at the front and back.
In addition to the front holes, there are also identically spaced holes in a flange at 90 degrees to the front face. These are used to mount support rails running from front to back of the rack. You put in rails to support each piece of gear that is too heavy to be supported just by the front bracket screws. The rails also make it possible to slide gear out, without having it interfere with gear above or below.

There are many kinds of fancy (=costly) rack-rails, but you can make your own simple ones from plain galvanized rolled-steel L-section. 2.5mm thick, 40mm sides. Work out how long they have to be to bridge between your rack's front and rear struts, cut a bunch to length (eg with a drop-cut-off-grinding wheel saw), then drill one hole at each end to suit the strut holes spacing.
The _height_ of the holes in the L section sides needs to be carefully worked out. Depends on the equipment bottom level, when the front brackets are screwed in. And get them all accurately the same, or the gaps between front panels will be annoyingly skew.

You'll need to buy a lot of the cage nuts and matching screws. The metric ones are M6. But some old racks have UNF #10 hardware.
For the M6, screws are typically 16mm long. I strongly recommend pan head philips head. Slot screws are a pain when you are trying to juggle a bit of gear with one hand while getting a screw to thread in with the other hand.
For inserting and removing cage nuts (you'll be doing this a lot) you can use a plain flat blade screwdriver, but I recommend making a thing like a bale hook. See pic.

There are special-purpose nylon washers that fit M6 screws, designed for racks. They have a raised lip and friction-clips that grip the thread so they don't fall off when you remove the screws. These protect the equipment front panels from being scratched by the mounting screws. I had found some of these, but so far haven't located a supplier to buy more.

Some of my writeups that include rackmount-related stuff.
http://everist.org/NobLog/20121017_the_last_rack_bender.htm
http://everist.org/NobLog/20121029_hp_racks.htm
http://everist.org/NobLog/20130923_hd_procrastination.htm
http://everist.org/NobLog/20130924_rack_roller_base.htm
http://everist.org/NobLog/20141212_racked_serendipity.htm
http://everist.org/NobLog/20160228_bench_rack.htm
http://everist.org/NobLog/20170224_summer_vacuum_odyssey.htm

Castors: need to be very heavy duty. A full rack can weigh many hundred kilos.
For safety, bear in mind that castors can turn in, which puts the load point back from the front of the rack. Beware the rack tilting forward and falling on you. My rack base frames put the front castors forward of the rack front to avoid this risk.

Castors with rubber rims, when left under load, develop permanent flat spots. So it's best to have some system to take the load off the castors when the rack is not moved for a while. I use screw-down bolts. Some racks have facility for these built in, others don't.

You don't need freely rotating castors on all four corners. Two fixed wheels, and two rotating castors, works fine. (Fixed ones at the back.) But some racks only have single bolt-holes for castors at all corners, so then use 4 rotating castors.

Buying racks-
Unless you _really_ want fancy looking ones, it's almost certain you should be able to get very cheap 2nd hand ones. Some of mine were free, some $50 each from a place that does telecoms work. Carriers etc often rip out old systems and discard everything, including the racks.
When they have front and back doors, these are always easily removable, by just lifting them off the pin hinges. So you don't _really_ have to have glass doors, just doors you can leave off when the equipment is in use.

Try to get racks that include adequate power outlet rails at the rear. You need an outlet per piece of equipment.
Having a master power switch at the front of the rack is very useful.

Other useful info
------------
19" rack
1 U = 1.75"  = 44.45mm (by the standard.)
Opening width: 450mm
Screw H spacing: 465mm
Facia width: 483mm (282.6mm / 19")
Usable equipment face width:  422mm

On the vertical mounting rails, the square holes for the cage nuts are 9.4mm square.
The metal between the holes has a repeating pattern: thin, THICK, THICK, thin, THICK, THICK, thin, etc.
ie it repeats every 3 holes. This is the 'single unit height', or 1U.
The lines on which the 1U modules (and all larger multiple Units) break is the _thin_ metal piece.
The three-hole group pattern repeats every 44.45mm.
Actual instruments will be about 1mm less than their n x U module height, to give clearance.

Rack unit heights   Blanking panels
-----------------------------------
1 U =  44.45 mm     43.2
2 U =  88.9  mm     88.6
3 U = 133.35 mm    132.9
4 U = 177.8  mm    177.4
5 U = 222.25 mm    222.0
6 U = 266.7  mm    266.2
7 U = 311.15 mm
8 U = 355.6
9 U = 400.05
10U = 444.5
11U = 488.95
12U = 533.4
13U = 577.85
14U = 622.3
15U = 666.75
16U = 711.2
17U = 755.65
18U = 800.1
19U = 844.55
20U = 889.0

http://www.brenclosures.com.au/19-inch-rack.htm

Specifications

A rack's mounting fixture consists of two parallel metal strips (referred to as "rails") standing vertically. The rails are separated by a gap of 17.72 inches (450 mm), and are a minimum of 0.657" (16.7mm) wide giving an overall rack width of 19 inches (482.6 mm).

The rails have holes in them at regular intervals, with both rails matching, so that each hole is part of a horizontal pair with a centre-to-centre distance of 18.3 inches (465 mm). The holes in the rails are arranged vertically in repeating sets of three, with centre-to-centre separations of 0.5 inch (12.7 mm), 0.625 inch (15.875 mm), 0.625 inch (15.875 mm). The hole pattern thus repeats every 1.75 inches (44.45 mm).

Racks are divided into regions, 1.75 inches in height, within which there are three complete hole pairs in a vertically symmetric pattern, the holes being centred 0.25 inch (6.4 mm), 0.875 inch (22.2 mm), and 1.5 inch (38.1 mm) from the top or bottom of the region. Such a region is commonly known as an "RU" or "U", for rack unit or unit respectively.


http://www.brdatasystems.com.au/PDF/Server-Rack-Specification.pdf
the SSI specifications visit www.eia.org/

https://www.eevblog.com/forum/projects/neat-control-cabinets-control-panel-wiring/
https://www.server-racks.com/rack-screws-10-32-12-24-m6.html
https://www.eevblog.com/forum/chat/what-are-these-old-style-rack-slide-out-rails-called/
  Chassis trak. A division of General Devices Co, Inc. PO Box 39100-Indianapolis, In 46239 - Phone (317) 897-7000.

[madires]

Rack frames always have same-style mounting rails at the front and back.

Do you know ETSI frames?

[Tomorokoshi]

Rack frames always have same-style mounting rails at the front and back.
...

I think you left out some detail!

[GreyWoolfe]

I use solid metal casters on my workbench that can support 136 kilos, all of mine rotate.  I wanted it that way.  You can also find them that can support more.  Don't use rubber casters, they absolutely will flat spot.  If you use metal casters, providing your floor will not be damaged in any way, you can eliminate the screw down bolts to take pressure off.

[james_s]

Are there any IT surplus dealers near you? I have seen more server racks than I can count get scrapped at various companies simply because nobody wants them. Granted most of these are the huge ~6 foot tall things standard in server rooms but smaller types are around too.

[Bicurico]

Hi guys,

Thanks for your great responses.
It will take me a bit to process all this information, as I am not familiar with some technical words used and need to look them up.
Also,  I will try to feed a pictured of my stuff so you get an ideas of what I have in mind and want to accomplish.

I will be back, but in the next days I simply won't have time... bear with me.

Regards,
Vitor

[Red Squirrel]

It seems even rackmount computer cases often don't come with rails, and you really want rails so it can be supported from the back too and not just the front.

What I tend to do is use "universal" rails and the system just sits on top.  Something like this:

https://www.ebay.ca/itm/4-X-Universal-1U-Rack-Mount-Shelf-Rail-for-Dell-Compaq-IBM-HP-APC-33-5-deep/282240947918?hash=item41b6df16ce:g:2zQAAOSw~HBaBKhH

There's probably better deals, that was just from a quick search.

So you install those, then the equipment would sit on top and slide in, then you can screw it into the rack as well. 

For the rack itself, if you get a 4 post rack as opposed to a fully enclosed one, it will be cheaper too, and cheaper to ship as you assemble it yourself.   You can always enclose it yourself by building plywood sides or what not, and add cable organizers.

You'll probably want to bolt down the rack too, that's a lot of weight if it tips over.   I have one in my basement but it's actual server stuff, I used sleeve anchors into the concrete.  It's not going anywhere.

[Bicurico]

Thanks!

And boy is that expensive!!!

Thats like 100 Euro per rail... Even if I get one for each group of 4 devices, that would cost me as much as a brand new rack.

I need to carefully study TerraHertz's great post and then investigate how much a custom wooden piece of "rack furniture" would cost.

The thing is, I need something that:

a) Looks good, so that my wife won't complain
b) Does not cost too much (in other words: it has to cost less than my next test equipment, modulator or whatever)
c) It must give me access to the front and rear. This means I need to be able to wheel it back and forth, as the normal position would be against the wall

Pictures will follow - I just haven't the time to grab them now.

Again, thanks!

Regards,
Vitor

[TerraHertz]

Also do an ebay search for rack mount shelf. These are useful where you have some small things that don't have rackmount brackets. Like the scope in pics below.

The point of looking through catalogs of new rack accessories like those rails, is not to buy them new (too expensive) but to know what to look for in 2nd hand disposals sales and salvages. In general, just getting an idea of various possibilities.

Also it helps if you have at least basic metal working tools and ability. Hack saw, angle grinder, drill, etc. Because rack-mounting often involves improvisation and hacks, to get odd things to fit somehow. Like with that scope shelf, the shelf rear lip turned upwards. I had to cut the lip off, and replace the reinforcing with a bit of aluminium extrusion screwed onto the underside of the shelf.

[cdev]

The LACK coffee table = 19 inch Rack - as in IKEA..

Use their cheap stackable tables to make an instant, super cheap rack..

They are exactly the right size.

[David Hess]

The LACK coffee table = 19 inch Rack - as in IKEA..

Use their cheap stackable tables to make an instant, super cheap rack..

They are exactly the right size.

You beat me to it but I will provide links.

https://www.ikeahackers.net/2012/05/rast-transformed-in-a-19-inch-rack-mount.html
http://www.ikea.com/us/en/catalog/products/44361109/

[VK5RC]

For a suggestion outside of the box.
As I have quite a bit of old HP iron, I would need about 5 or so,  6 foot high racks, with rear access needed, and moving a 6" high stack of old test gear in a rack is not happening soon, I went for the Pallet Rack style of shelving: really strong, very cheap, access all sides. Also strong enough for me to climb it if needed!
Robert.

[Bicurico]

I liked the Ikea suggestion!

I will have a look at it. Seems cheap and customizable. I actually think I have such a small table in the living room, so off I go for some tests. If my wife approves and it really works, then I might just stack the devices next to my desk and actually get some extra space for the small TV on top of it.

I will report back tomorrow, when I have some time.

Regards,
Vitor

[Bicurico]

Indeed, the Ikea square table is a neat fit! Never noticed it before.

I think they cost like 10 Euro each and with three I could assemble what I need.

But here is a question: the tables are made of something closer to cardboard than wood. How do they handle the weight?

[Bicurico]

Well, for 6,99 Euro I will give it a try! I think I only need 3 or 4 of these tables, as well as some extra screws.

I have shown it to my wife and she gave me a go ahead = points earned on the HWAF!!! 

[tooki]

I was building a test equipment that has 5 main components in rack units from 2U to 3U. Our IT person told me that rail racks can be very expensive, so we ended up just stacking them by gravity and cram them into a 20 year old rack that was used to house a signal generator and a Tek 2445.

So yep, beware the cost of the rails.

Just a reminder that some equipment (especially 2U servers) is not designed to stack except when mounted on rack rails. This stuff uses thin housings very close to internal components, and cannot handle any pressure — the housings are literally just to keep dust out.

[cdev]

Keep in mind that Lack tables are very flimsy. They wont hold your gear securely unless its very light and only has its weight right at the very front, and is otherwise empty, or unless it relies on the item right below it for support.

As coffee tables, they are cheap crap. The legs eventually fall off without any actual misuse..

I have a broken Lack-sized (the wood one) table in my basement, that I've been meaning to try to figure out how to fix. Its not the first time this has happened.

The "Rast" idea above looks stronger, but again, there is no rear support.

[Bicurico]

Ok,

Here two pictures:

1) As it is now. I have to agree with my wife, it is not a great sight...
2) Mind my Photoshop-skills (actually I just used the plain MS Paint): this second picture is how I image the result using 4 LACK tables from Ikea. Actually, not bad at all. Might not receive an interior design award from the common home magazines, but cetainly a big improvement.

Regarding the weight and robustness of the devices: they are all heavy and very robust. In fact, they are already all just stacked on top of each other. I just glued rubber feet on each, so to create a few mm space between each device.

Also, note that I do not turn them all on at once. I might for instance be interested in trying out a DVB-T receiver, so I would turn on the MPEG4 encoder, the DVB-T modulator and perhaps one CRTU for signal monitoring. For a different setup I would switch on other devices. Using the LACK tables, my expectation is that only up to 5 devices get stacked, before there is the table top, which is supported by the 4 legs. I would consider using an L shaped metal piece screwed to each leg and table top, for increased resistance. No wheels, as everything is simply to heavy. Instead I would just leave like 30cm on the back for some access - that would still be better than current situation.

Thanks for all feedback, you guys helped me a lot. I will post the result as soon as I get my hands on it and I let you know about the overall HWAF increase... 

Regards,
Vitor

[tooki]

Just a reminder that some equipment (especially 2U servers) is not designed to stack except when mounted on rack rails. This stuff uses thin housings very close to internal components, and cannot handle any pressure — the housings are literally just to keep dust out.

Mine are stripped from a few Tek current probe excitation power supply units, and they are built like tank.
One of the boxes houses a 1.75mH, 160A, 100kHz inductor bank, weighing totally 100+ pounds.
After stacking that one, as well as 2*40 pounds capacitor banks on top of a third capacitor bank, the third case has absolutely no visually visible deformation at all.
I tried to stand and jump on even the center of the lid of one completely empty chassis, and there's no wobble at all, and I'm 200 pounds.

Um ok, that’s fine. I just posted it as a reminder, lest someone else think it’s OK to stack any kind of equipment. Some rack mount equipment is really sensitive to weight, so one needs to be aware of this. That’s why I used the word “some”.

[tooki]

Ok,

Here two pictures:

1) As it is now. I have to agree with my wife, it is not a great sight...
2) Mind my Photoshop-skills (actually I just used the plain MS Paint): this second picture is how I image the result using 4 LACK tables from Ikea. Actually, not bad at all. Might not receive an interior design award from the common home magazines, but cetainly a big improvement.

Regarding the weight and robustness of the devices: they are all heavy and very robust. In fact, they are already all just stacked on top of each other. I just glued rubber feet on each, so to create a few mm space between each device.

Also, note that I do not turn them all on at once. I might for instance be interested in trying out a DVB-T receiver, so I would turn on the MPEG4 encoder, the DVB-T modulator and perhaps one CRTU for signal monitoring. For a different setup I would switch on other devices. Using the LACK tables, my expectation is that only up to 5 devices get stacked, before there is the table top, which is supported by the 4 legs. I would consider using an L shaped metal piece screwed to each leg and table top, for increased resistance. No wheels, as everything is simply to heavy. Instead I would just leave like 30cm on the back for some access - that would still be better than current situation.

Thanks for all feedback, you guys helped me a lot. I will post the result as soon as I get my hands on it and I let you know about the overall HWAF increase... 

Regards,
Vitor

I wouldn’t trust those Lacks stacked like that. That’s potentially a lot of weight being supported by the bottom one. I’d go for a used full height rack, which as others have said, can be found fairly inexpensively used.

[cdev]

Don't put equipment flat on the floor- that is asking for all sorts of trouble..

The level of dust rises exponentially when you get near a floor or wall, for one thing. Also, water.

[Bicurico]

Two notes on my intention:

a) The LACK table is actually not supporting any weight, since the devices will continue to be stacked on top of each other. The legs of the table seem robust in Z direction, so they will help ease the weight on the lower devices.
b) The first device is put on the LACK table top, which is upside down layed on the floor. Because the LACK table top is made out of cardboard, it will actually attenuate any load on the floor and/or uneven floor. This will lift the first device around 6cm from the floor, which is made of tiles, so there should not be too much dust.

Let's face it: 4x LACK table = 28 Euro. Add a few screews and L-shape metal connectors and it should still be under 50 Euro. This should considerably improve the HWAF at such a cheap cost, that it is worth the try.

What I REALLY wanted is a new, good looking rack. The best I found is this one: https://www.castroelectronica.pt/product/armario-bastidor-de-pe-19-42u-800mm-com-porta-vidro--proftc

However, it already costs 600 Euro and now I need to add the extra supports! Simply too expensive.

A second hand rack would be an alternative, but I have to wait for a good opportunity (price and cosmetic condition) and then I have to see what can be done in regards to supports.