Film-Tech Forum ARCHIVE: Supporting rack mount equipment

This is topic Supporting rack mount equipment in forum Digital Cinema Forum at Film-Tech Forum ARCHIVE.

To visit this topic, use this URL:
https://ft-forum.com/ft/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=16;t=003609

Posted by Frank Cox (Member # 6258) on 03-01-2019, 01:02 AM:

One of my amps died and I just replaced it. My sound rack has no rails so the only thing holding the equipment in place is the bolts through the wings on the front panel.

As it happens, the amp I replaced was the bottom one in the rack so I actually managed to find a box that was exactly (to the fraction of an inch) the right size to sit between the amp and the bottom of the rack to support the amp while I removed the bolts, changed the amp and put the bolts back.

The amps aren't hugely heavy but they aren't nothing either. They're QSC DCA2422's and the spec sheet says they weigh 21 pounds.

So my question is, how are you supposed to support these things when you remove the bolts so they don't fall down or drop onto the next component below them in the rack? Pulling everything out of the rack from the bottom up to the faulty component seems pretty inefficient and I'm not sure I could find a box to fit each iteration if I had to change the amp at the top, for example. I don't think I could hold it from the back with one hand and undo the bolts at the front with the other; I don't think I could support the weight that way and I don't think I could reach that far.

Is this stuff just supposed to be a two-man job and that's all there is to it, or am I missing some clever trick?

Posted by Tony Bandiera Jr (Member # 2365) on 03-01-2019, 01:50 AM:

First off, if all of your amps are DCA's there is no need to mount them with empty rack spaces between them...I have always stacked them from the bottom up, so only the bottom amp would require support if needed. They have flow thru fan cooling and no vents on top or bottom.

If you have one rack space between amps, the trick I always used was 35mm film cores or trailers. It was close enough to the required height that the amp would not fall far enough to be an issue. For other spacings, I would stack cores or trailers.

As for getting one out in the stack, I would remove the four screws then push the amp out partway from behind, then use the rack ears as handles to take it out the rest of the way. Easy peasy.

The same principles apply with other equipment, and for processors and the like, I tend to remove all but one screw (usually leaving the bottom left corner), loosening that last screw until just a few threads were holding it.

I then put my right arm under the equipment, to support it, then took out the last screw with my left hand. Then, pull the equipment out with both hands.

As a tech doing service calls solo, these were the only ways I found to work for me with minimum fuss.

Posted by Marcel Birgelen (Member # 6801) on 03-01-2019, 05:47 AM:

I've never really seen an equipment-rack with rails, those rails are usually provided by the manufacturer of the equipment itself.

Most audio-equipment however, is supposed to be mounted in a 2-post fashion, without rails.

Those 2U QSC DCA units are made to be stacked, as long as the airflow at the front and the back is sufficiently guaranteed.

So, when you stack them with no space in between, it's usually pretty easy to get one out and back in there.

The only thing that annoys me is that the mounting holes in the rack ears are in the most outward position, this sometimes clashes a bit with cage-nuts and bolts of equipment that's directly adjacent, in many cases, other DCA units.

For really heavy equipment, that doesn't come with rails, I often install a 19" rack shelf first. That way, I can slide it onto the shelf and then mount it to the rack posts. Depending on how much it will sag on the backside, I might decide to leave the shelf in there.

Posted by Carsten Kurz (Member # 5396) on 03-01-2019, 05:55 AM:

Frank, at some point I had to do the exact thing, and solved it with a few foam bumpers I cut from a lamp packaging. I just place them below the amp to be moved out, you can cut them to size so they just sneak in between and nothing's falling down. If you cut them small enough, you can leave them sitting there, or store them somewhere after you have taken them out when the new amp went in. I'm sure you'll be able to find thick foam in some boxes you stored somewhere, or, go to a white goods store and request some of their packaging. Usually they'll be glad to get rid of some.

- Carsten

Posted by Steve Guttag (Member # 268) on 03-01-2019, 06:33 AM:

Wow...you find it hard to pull a DCA amp by yourself? Those are lightweight amps. Try it with an MX1500 (or MX2000 or MX3000).

As others have said, there is zero reason to separate the amps but if you choose to, remove the blank below it. Remove the two top screws FIRST. Then remove one of the bottom screws while supporting the amp so it does just lower on its own (it will want to pivot via the remaining screw). As you unscrew the last screw, the amp will start to lean back and again, support the front as the screw comes out. Once the last screw is out, ease it down on the front. Slide it out.

Reverse for reinsertion. Depending on the length of your rack screws and your finger mussels, you may need to device some assistance. For instance, put the blank back in first so it helps support the front. If your screws are long enough and you can push hard enough with your screw gun/drill (or even your hand if you are just using manual screwdrivers) you can get it to raise up just with the screws. Otherwise, most anything will prop the rear up from what is below it. It need not be precise. You just need the face of the amp close enough for the screw to catch. Once your bottom screws are almost all of the way in, remove your rear prop or risk it getting pinched into place.

Now, if you did have a heavy amp like the MX series, then yes, I like using rear hangers as it not only supports the amp better but makes installation easier since you can slide the amp in, lift up on the rear and put the screws in on the rear hanger to support the amp.

Loading/unloading amps as a repair is not a 2-person job but if the other person is there, then by all means use them to make it an easier job.

Posted by Sean McKinnon (Member # 612) on 03-01-2019, 07:58 AM:

We use rear rails and vertical lacing bars in all of our racks. These things make cable management and equipment mounting so much easier. We will often use shelves upside down or horizontal lacing bars on the rear rails to support equipment that doesn't have rear mounting rails.

Posted by Dave Macaulay (Member # 813) on 03-01-2019, 11:02 AM:

These amps don't need rear support, although it is possible with an accessory if you have a rear rail positioned correctly. We do this when a stuffed rack has to be shipped, although preferably just the rack wiring is completed and the amps shipped separately. Much lighter rack to get up the inevitable stairs as well.
Doremi chassis servers can hang on the front bolts but it's marginal, threaded hole racks tend to strip the rail threads eventually. Racks with snap-in nuts are better for that since the nuts are stronger and can be replaced (but those nuts are a PITA). There is a slide kit for Doremi if you have a rack with rear rails.
A (crazy long and heavy) Dolby DSS200 definitely must be supported at the rear or be on slides (included with the servers).
The trick assembling racks is to mount the bottom amp first, then use a spacer (like cardboard) between each amp or pry each up a bit when tightening the screws. This leaves enough clearance to slide any amp out, none are clamped in place. Using 1U panels between amps is fine if you have the space, you still have to leave some clearance between components. If you have saved a few old 35 cores they are close enough to 1U height to use as spacers while you screw in an amp or whatever. When assembling new racks I like to lay them down on their backs and drop the amps etc in, much easier and it's simple to space them out so none are held in tight by those above.

Posted by Steve Guttag (Member # 268) on 03-01-2019, 01:11 PM:

For the record, I HATE HATE HATE caged nuts. Using decent screws and racks, I've never had a tapped hole strip out. Cage nuts, aside from the absolute pain they cause (physical) also have the equipment sag a bit since they also act like a cheap-ass spacer to the equipment (the clip part comes between the equipment ear and the rail).

As for loading racks...the best way? On their backs (typically with a piece of wood to allow lifting them vertical when done under the rack near its top).

And YES always center the equipment vertically on the screw holes so equipment can be slid in/out without being jammed by the thing above it.

Posted by Sam D. Chavez (Member # 1841) on 03-01-2019, 03:20 PM:

There must be a trick to inserting cage nuts. The ones with the Christie bases seem the worst. I waste more time installing these than any other single task in the process.

Posted by Sean McKinnon (Member # 612) on 03-01-2019, 03:29 PM:

Caged nuts and square hole racks are EVIL! I think they are much more popular in the IT world. We (BLS) use Middle Atlantic racks pretty elusively and almost always the WRK series with the removable side panels unless theres a reason not to. One great thing for Atmos installs is to use the optional wire raceway for the wrk series. Yes, Middle Atlantic is pricey but they look nice and i've never had an issue with one of their racks. Now their Mid Atlantic branded electronics on the other hand...

For projector pedestals I really like the MIT pedestal. One thing I like to do sometimes especially if I am putting a christie power supply in there is to order another door and provide access to both sides if you dont need the rack space.

Posted by Steve Guttag (Member # 268) on 03-01-2019, 04:12 PM:

+1 on Middle Atlantic racks. We use mostly ERK series for sound. Only the WRK if we need the extra channels. The only reason we would use removable side panels is if we were ganging so of the WRKs, quite a few have been the WRK-SA style.

Posted by Marcel Birgelen (Member # 6801) on 03-01-2019, 04:39 PM:

quote:
Caged nuts and square hole racks are EVIL!

Well, yes, it's not always rosy, but you learn to live with it. We also prefer to standardize. Try to mount any IT equipment with their standard rail-sets into a rack with round holes for example. [Wink]

quote: Sam D. Chavez
There must be a trick to inserting cage nuts. The ones with the Christie bases seem the worst. I waste more time installing these than any other single task in the process.

You need one of these. It avoids getting your fingers stuck between nut and cage or experiments involving screwdrivers and pliers. [Wink]

We order cage nuts by the bag of 100 or so from Rittal, which we also order most racks from. It's a German manufacturer and they're kind enough to put one of those little metal tools into each bag of cage nuts.

Posted by Adam Martin (Member # 641) on 03-01-2019, 08:28 PM:

For cage nuts, I use a cage nut insertion tool.

Posted by Dave Macaulay (Member # 813) on 03-02-2019, 08:35 AM:

+1 for Middle Atlantic racks, and their custom power bars are great. The legacy racks we work on that get stripped threads are not MA, their threaded rails are formed from thinner sheet metal. MA rails are thick and stout.
Christie pedestals have always been evil. The removable sides are good, yes, but the snap nuts are horrible... and why 1/4" threads rather than the almost universal (for audio racks) 10-32? Plus no way to support the rear of a deep server or slide rails. The Barco standard pedestal is pretty good other than its screw on side panels, I think maybe MIT makes them for the Americas? Not a fan of the Barco flat pack pedestal.

Posted by Steve Guttag (Member # 268) on 03-02-2019, 08:56 AM:

Here's the thing about the "servers" as the reason for using a caged-nut type rack rail system.

At first I liked them for when we did Dolby DSS servers...Dolby supplied the slides that just clicked into the holes. But then it dawns on you...so that saved you 3U worth of mounting and the rest of the equipment you'd be fighting to Effin caged nuts and again, they don't hold equipment well without sagging.

Dolby supplied you with the adapters to use traditional 10-32 rackrails so what was the big benefit there? So screw the cage-nut system for most of what we do in cinema.

If I were put in a server farm like some IT people do, then yes, I'd see the advantage. But if you are mostly putting in traditional equipment with maybe one piece that needs the hole-type rail, then screw that. Adapt the one piece to the 10-32 system.

There are just too few benefits to the caged nut system (which are really just the adapters for things that don't use the holes directly). The negative column is just overwhelmingly long.

Dave, funny you mention the Christie pedestal...that didn't consult anything for its dimensions. It is too long for most servers of the day and too high for standard lens heights used in the prior art (film). The current pedestal is a bit better in the height department.

What one of our techs did with the Christie pedestal is take the supplied rack rails used for forming two horizontal racks and band saw them apart. Then using suitable standoffs (I believe he made them himself out of square stock and drilled a hole down its length) made standoffs for them to provide an inner set of rails so normal server lengths (DSS200) could be used. But who wants all of this in "kit" form...which is part of what a caged nut system is.

Posted by Bruce Cloutier (Member # 9615) on 03-02-2019, 10:48 AM:

Geez. This thread is seriously causing me to rethink any interest in supplying rack-mountable product. Here I thought you all loved it. I wonder what exactly is the attraction then? I bet it is a short list. I get it that it all looks cool afterwards. There is the 1U/2U/3U 19" face size standardization. Not to mention that there probably isn't an alternative. But I am sensing that it is somewhat of a pain in the ass. And, even though it is somewhat of a standard it varies quiet a bit manufacturer to manufacturer. Great. [uhoh]

Posted by Tony Bandiera Jr (Member # 2365) on 03-02-2019, 11:30 AM:

Bruce, don't panic.

Very few racks in cinema use the dreaded cage nuts and only Christies' pedestals don't follow the standard.

19" is the most common rack standard, IT server farms can use 19" (or at one time 21") and almost always use cage nuts.

It's not the equipment that is the issue, it is the rack manufacturer's use of cage nuts (which are as horrible as everyone has said) instead of a standard rail pre-tapped for 10/32 screws.

Speaking of that, even with oddball screw threads, the mounting holes on the equipment are always the same location and dimensions.

So move forward on rack mount products, and don't sweat the rack manufacturer's stupidity.

Posted by Steve Guttag (Member # 268) on 03-02-2019, 11:47 AM:

Bruce,

And be slick about your product. If you supply it in a rackmount case, think about having it on slides too so one can service by merely sliding it out and lifting the top off.

Either that or bring your IO out to the rear of your rackcase (probably preferred as moving things need all cables sized to handle the equipment moving in/out).

I don't see any bitching about rackmount stuff...just the caged nut method.

Posted by Bruce Cloutier (Member # 9615) on 03-02-2019, 01:23 PM:

quote: Steve Guttag
And be slick about your product. If you supply it in a rackmount case, think about having it on slides too so one can service by merely sliding it out and lifting the top off.

Okay, off-topic, but yeah... I've struggled with access to the rear and the ease (or rather difficulty) one would have with adding I/O connections. So Steve, exactly, I have been contemplating some type of drawer with strain reliefs for the cabling to support easy access to I/O. The thing is to find a way to do it so it doesn't weigh 30 lbs. and cost 3X more than the electronics.

So I understand, Frank started this discussion because the heavier equipment is difficult to mount without growing another set of hands, right? Some of the equipment has handles on the front to help with holding it but you still need to somehow will the screws up off the table, thread themselves and tighten in place. My wife keeps want to wiggle her nose to make stuff happen (like Samantha from Bewitched). She also wants a Star Trek Replicator but all of that is another story and a separate issue for me.

In our case I would be concerned about the weight of cables pulling down on the unit. It's a concern with these plastic rack housings from Bud Industries that we were evaluating. I can see the tabs breaking or warping under any real strain especially in a warm installation. The plastic just doesn't give the quality feeling that we want. The cost is damn attractive. I just wish that I had a machine shop here for prototyping.

I assume everyone expects the black equipment. The QSC Core is pretty sleek with the brushed look and blue graphics screen. Hard to do and keep the pricing disruptive.

Posted by Frank Cox (Member # 6258) on 03-02-2019, 02:31 PM:

Bruce, I'm no kind of an industrial designer, but it seems to me that all you need is a what amounts to rack-mountable tray. Since the Jnior is a relatively small unit (or at least the one that I have is), all of the electronics should fit into the front couple of inches of the tray. Put the connectors there as well, and just allow the wires to flop over the back of the tray and hang down from there. The tray could have little cut-outs in the back wall for the cables to go through, possibly lined with plastic shields so the wires won't get cut into while hanging. Is there such a thing as a strain relief that can be easily opened and closed? If so, maybe that's what you want there.

Then all you need is a plastic cover for the front part of the tray where the electronics are so nothing gets shorted out. Now the heaviest part of the case will be just the tray, and a tray doesn't weigh much.

To service it (disconnect and connect stuff) all you have to do is unscrew the tray and pull it out two or three inches. The back of the tray can stay inside the rack so the whole thing doesn't fall on the floor, and the connecting wires need to move in and out just three or four inches, so you probably don't need to make any special provisions for that either.

Posted by Bruce Cloutier (Member # 9615) on 03-03-2019, 07:07 AM:

Of course if we are talking about the current manifestation of the JNIOR, one could mount it in a rack mounted keyboard drawer for a clean installation. A tray would work as well. Or, it can be affixed to the back of a 3U blank. It can be strapped to the back of the rack or left on the floor. Those last approaches work but make me cringe.

I am hoping to create a rack mountable version that brings status to the front and maybe some controls. Possibly some combination of the control panel we have and a version of JNIOR. The mechanical hardware takes a commitment in quantity in order to keep cost down. So I need to be confident in the design from the start. Basically, the reason that we don't already offer it.

Sorry. Didn't mean to hijack the thread.

Posted by Marcel Birgelen (Member # 6801) on 03-04-2019, 02:45 AM:

Not all is perfect in the 19" rackmount world, but in general, it beats the alternatives.

You want all your operational equipment neatly organized into a bunch of 19" equipment racks. You also want to route all your input/outputs to those racks. All equipment that doesn't really fit into it, is a bit of a pain, because where do you put it and what do you do with the wiring? Do you slap it against the wall? Do you strap it into the rack somewhere, nobody even knows it's there?

So, I guess a 19" rack-mountable JNIOR or a tray to make it rack-mountable is still very much welcome.

Nonetheless, there are endless discussions on where your wiring should go, for example, and if the front of your appliance should be control-only, or if it's "cool" to have inputs and outputs there too?

In general, the consensus seems to be that your wiring goes on the backside of your equipment and the front is just for control.

That obviously creates a bit of a problem, if your appliance rather "shallow" and has to share a rack with those deep monsters like some amps, most servers or some of those deep switches, especially if it's just 1 or 2 units high.

A noticeable exception is networking gear, where wiring is mostly found on the front-side of things. That's also why, in many cases, switches are put on the backside of racks as so called "top-of-rack" switches.

Another issue is how to do ventilation right. Now, for heavy IT equipment, the standard is that cold air is drawn from the front and exhausted at the back. This is also the case for cinema servers and gear like the Dolby CP850. They draw cold air from the front and exhaust it to the back of the rack.

Amplifiers can be a mixed bag. Those with fans in them, seem to stick to the rule though, that heat exists to the back of the rack.

Posted by Steve Guttag (Member # 268) on 03-04-2019, 05:10 AM:

Smart amplifiers (QSC) vent rear to the front. The hole front-to-rear things is just plain stupid.

If you vent front-to-rear, then each piece of equipment has to filter its air and then each piece of equipment puts heat into the rack, thereby heating the rack.

For rear to front, then one only need provide a single filter system for the entire rack and the heat generated is expelled by each respective equipment. I typically provide a fan package at the bottom behind a filter to draw clean cool air into the rack. This also pressurizes the rack which really cuts down on dust accumulating in the rack too. One only has to keep the one filter clean instead of cleaning each piece (if they have filters at all).

Posted by Marcel Birgelen (Member # 6801) on 03-04-2019, 05:34 AM:

Yes, you're right, most QSC amps with fan draw in air from the rear. Many older, passively cooled amps don't seem to have a particular flow.

But that's why I try not to mix amplifiers with servers in the same rack, but that's not always a possibility.

The Front-to-Rear ventilation style of IT equipment comes from the datacenter, where the cool air is usually let into the front, where most of the "operational work" is done and the hot air is removed at the back (the cold/hot isle principle).

Some switch manufacturers let you choose the cooling flow, as they offer different models for "back-to-front", "front-to-back" and sometimes even "left-to-right" and "right-to-left" cooling options.

quote: Steve Guttag
If you vent front-to-rear, then each piece of equipment has to filter its air and then each piece of equipment puts heat into the rack, thereby heating the rack.

With mixed equipment in a rack, in my opinion it's better to have the backside of your rack sufficiently ventilated. Or else you end up having your amps sucking in hot air from your server.

Although a booth hasn't to be a clean room, I consider it to be much more like a datacenter nowadays, so make sure you filter the air that's going into it. It will also improve the longevity of your projector.