Homemade Rack Cases
NOTE: Making your own rack cases is one of the simplest do-it-yourself construction projects imaginable if you use prethreaded rack rails, because the rest of it is just a box. Larry Mundy is an occasional contributor here, reachable at firstname.lastname@example.org or through www.yournamehereband.com.
3/03 - Larry Mundy http://www.colomar.com/Shavano/rackcase.html
Most professional PA-system components, and many musical-instrument components, are built for rack-mounting. This means that they are a standard 19 wide and their height is in some increment of 1-7/8, commonly known as a rack unit or rack space. Many components are 1U, or one rack space high; others may be 2, 3 or more units high. What they will all share is a common mounting system and mounting-hole spacing, so that rackmount components can be mixed and matched within a rack, which is essentially a big box with a mounting surface near the front that accepts 10-32 "rack screws" into holes spaced according to the standard. Since you provide the box, these components have simple metal enclosures, and that saves both you and the manufacturer some money.
The same standard is shared by heavy-duty computer components servers and such used in arrays and combinations for large installations. And its used in recording studios, where the rackmount standard likely originated; many of your rackmount PA components would be equally at home in a recording studio. Studios and computer installations, however, dont get moved around much and instead of mounting boxes, sometimes just use sturdy exposed rails where the back and sides of the components is just open to the air. This is very convenient for recabling, repair and even cooling, but of course it would be a silly way for a touring band to cart stuff around. What you want is the equivalent of those mounting rails, boxed up in a sturdy enclosure.
Rack boxes can be purchased factory-made at music stores, and lots of other places. There are three principal types. One is the molded-plastic type sold by SKB, Gator and others, which combines a very tough plastic housing with molded-in aluminum rails:
Molded plastic rack box, strong and light, but pricey.
The principal advantage of these is that they are very lightweight. They are also sturdy, at least for applications that only require a few rack spaces. They have removable fronts and backs that usually fit tightly enough to repel a bit of rain while you haul them in from the truck or van. The downside is that they look like giant Tonka toys, and for the most part, they are the most expensive plastic boxes I can imagine, with prices easily running from $100 on up. Way up. And the rails tend to be perforated-aluminum strips that aren't prethreaded but require little "spring nuts" to be positioned on them. When you lose the spring nuts (you will), you will find replacements pricey as well.
Another type is the flight case variety, sometimes called an "Anvil" case after a noted manufacturer, which are built to take (or built to look like they will take) the sort of rough handling airline baggage handlers impose on suitcases. They look like the steamer trunks you see being loaded onto ships in old movies, with metal strips over all the edges, big metal corners, huge locking clasps and (usually) some sort of very impact-resistant material like formica covering the wood beneath. Really fancy ones may even have spring-and-foam suspensions to cushion the components inside from jarring impacts. These are the best types of cases you can get. They also can cost as much as the stuff thats in them.
"Flight" cases offer the best protection, but at a price.
Finally, there is a sort of cottage industry building carpet-covered wood cases used by bands, DJs, or even as coffins for very, very short people. While some unscrupulous and/or silly manufacturers use particle board (read some of my other articles for rants about this stuff. It is totally unsuitable for serious use), most use a good grade of plywood. Toward the front are a set of prethreaded rack rails bolted to the cabinet sides. There are usually removable fronts and backs for transport. Heres a 4U store-bought example, which was about $130 at the local Guitar Center:
"Store-bought" wooden rack case, carpet-covered, with clasp-on cover
Wood cases work fine for light touring use, and have the advantage of better matching your carpet-covered speaker cabinets. They have the further advantage of being buildable in your own garage at a fraction of the store-bought cost. Basically, they are a carpet-covered plywood box with a couple rack rails mounted inside. Nothing too difficult there. The other advantage of building your own is that you can size their depth for your specialized needs.
For example, I have a Fender SPA750 power amp from the days when Fender made a full line of pro-audio equipment; we use it to power onstage monitors. It packs 750 watts RMS into the height of a single rack space, which is pretty amazing. Unfortunately, it accomplishes that feat by being over 20 inches deep, which is a nearly-obscene dimension in the premade-rack-case world. Many rackmount effects boxes and power strips are only a few inches deep, and will fit in any rack in the world. Most large power amps are 15 or 16 inches deep, and so heavy that they require additional support at their back corners; these require rack-box dimensions of 18 inches or more, because the front needs to be recessed for the protruding knobs and the rear needs a little working room for rear support brackets or whatever. But a 20-inch-deep amp with front knobs and requiring rear support simply would not fit in any premade case I could find at any music store, and in the Dallas-Ft. Worth area where I live, there are a whole bunch of music stores. So, out came the plywood and glue. I wont belabor every step of construction and carpet-covering, because Ive already done that in my Speaker Cabinet Project in Words and Pictures article. Ill just highlight whats different about this task.
There is no air pressure inside a rack case, no thundering bass speaker. Its only job is to hold all your rackmount stuff together and allow it to be carried from place to place. Ive found ½ plywood is plenty sturdy for this purpose, if copious internal bracing is used. There is nothing wrong with using thicker plywood, other than a little weight penalty. For large cabinets that will hold heavy components, thicker wood is a good idea, or at least a double-thickness floor if you will be attaching casters.
You will be buying premade rack rails, from Parts Express or somewhere similar (Ive found that Mars Music retail stores usually have a stock of these as well). They are a simple length of L-shaped steel, prethreaded for rack screws on their face and with mounting holes on the side. They are sold in pairs (duh) and in lengths that are multiples of two rack spaces 2U, 4U, 6U, 8U and so on.
Prethreaded rack rails have 10-32 threads on one face in 1/2-U spacing, mounting holes for 1/4" bolts on other face.
My first bit of semi-useful advice is, buy rack rails, and build rack boxes, with more spaces than you can currently use. You will probably accumulate more stuff in the future, and if you cant just bolt it into your existing rack, you will have to build another, bigger one. I know having gaps in your rack, like a 6-year-olds front teeth, can look kind of silly. But you can buy inexpensive rack-width blank plates 1, 2, or 3 units high to fill those empty spaces until you have the means or need to expand. When you do that, Id advise that you buy multiple single-space vented (i.e. slotted or perforated) ones for reasons Ill explain later.
A perforated blank plate, 1U high.
At the same time, resist the urge to get 30-space rack rails and put them in a huge box, on the theory that you now have infinite expandibility. You dont want to carry that big empty box to gigs. And, chances are good that you will want your box to hold one or more power amplifiers, which can weigh 30-50 pounds. Unless you spend hours at the gym every day, you cant lift a big box full of power amplifiers, and the stress on the wood and handles will cause these things to fail over time. My advice is, if you need 30 rack spaces, distribute that over multiple boxes that can be stacked and wired together with a minimum of fuss.
A stack of two homemade, 20 high rack cases for PA use. The top one has 10U of rack rails, and holds a mixer, effects, EQ and a monitor power amp, so it can be used by itself for practices. The bottom one holds a larger power amp, compressor and some associated components, and has an empty chamber at the bottom where we store speaker and power cords and have installed an inexpensive AC outlet to plug in the "power strip" from the top cabinet. Stacked together, it is comfortable to use while standing, and neither case separately is too heavy to handle.
The interior width of your rack box will be a little over 19 inches. In fact, it should be just a bit wider than you think it should be, to accommodate the carpet covering that will wrap around the face of the box and will probably space your rack rails at least 1/4" closer to each other than they would otherwise be (it looks best if the carpet wraps under the rack rails). Since this sizing is critical, consider sizing the box in place around your equipment. Bolt some rackmount equipment (or even those blank plates) into your rack rails (choose sort of the midpoint on the equipment rack holes if they are egg-shaped). Then cut your plywood to fit around that width, plus at least ¼-3/8" for the carpet wraparound. If your box ends up a little too wide, you can always space the rack rails out from the sides with some washers. If your box is too narrow, youre screwed. So you know which way the margin of error should go, huh? You should also make the box a little taller inside than the rack rails themselves dictate, by even more than the carpet-wraparound dimension. The component you may want to place at the bottom of the rack may have little rubber feet that have to be removed otherwise. The corner bracing will eat into the vertical space from the top and bottom. A second floor for mounting casters or feet will impinge on interior space. You want every rack space to be useable someday, even if its empty now.
The depth of the cabinet is dictated by the depth of what you plan to put in it, but recess the rack rails about 1-1/2" from the face of the box to allow for knobs, etc. on the front of your equipment, and give yourself extra space in back so that plugs, etc. inserted into your equipment don't project beyond the rear if you don't want them to. A little extra depth also helps when you replace one component with a deeper one someday. When you have the dimensions figured out, attach the sides, top and bottom to one another with bracing, wood glue and drywall screws, as described in the other article(s) on this site. As with my speaker cabinets, I try to maximize strength by butting the sides to the top and bottom plates and using oversize (3/4 X 1-1/2) bracing, with 1-1/4 and 1-5/8 drywall screws run into that from the outside at least every three inches. Stop the bracing short of the face; recess them from the front at least as much as the rack rails will be. Then position the rack rails where they will go, and drill holes through the mounting holes and on through the sides of the box.
All the weight of the rack-mounted equipment will rest on the rails, which will transfer that weight to the plywood case along the rather small area near the face of the box where the rails are mounted. The most critical concern is that the rails are mounted to the plywood very, very securely. Little short wood screws into thin plywood simply will not work. You will need as many ¼-20 T-nuts as you have mounting holes in your rack rails, and a like number of ¼-20 bolts which are no longer than the thickness of the plywood and any wraparound carpeting, plus the thickness of the rack rails themselves. 5/8 or ¾ usually works. The T-nuts are placed on the outside of the cabinet, where they will later be covered by carpeting. Run a test bolt through a washer and tighten the T-nuts until they are just about flush with the plywood surface and wont show up as ugly bumps on the exterior. You can lay the box on its side on a concrete surface, t-nuts down, and whack it on the inside to help seat the t-nuts. Every time you re-rack a bunch of stuff, check the tightness of the bolts that attach the rack rails into these nuts.
If you have a power amp that requires rear support, see if you can place small pine bracing or metal L-brackets inside the cabinet in a way that makes this support easy. Sand or file off the cabinet corners so the carpet will go on smoothly. You are ready to carpet the box. First, I'd recommend you paint the whole thing with flat-black paint inside and out. You will see the inside, a lot, and it looks better if its finished somehow. You will see the outside if your carpet gets torn, burned or sliced, and the same principle applies. Then carpet the box as described in one of my other articles on this site. I use black or grey carpeting, but this stuff comes in all colors if youre so inclined.
If this were a speaker project, I would have told you to cut holes for recessed handles before carpeting. But you cant use recessed handles because they will project too far into the interior of the box and make at least some of the rack spaces unusable for full-width components. So for this application, get some heavy exterior-mounted, spring-loaded handles, and mount them slightly to the front of the centerline of the cabinet since thats where the most weight will be.
These handles sit fairly flush against the cabinet side and because they are spring-loaded, dont flop around and buzz if the bass amp is next to them. They will have at least three mounting holes, usually sized for #10 bolts. Again, use T-nuts and bolts, NOT wood screws, for attaching these. The entire weight of the cabinet and all its expensive contents will be supported by these few bolts. Check their tightness from time to time.
Now you can mount the rack rails, and youre just about done. Before tightening the rail-mounting bolts into the T-nuts, test-fit a couple components or blank plates into the rails. If the rails are too far apart, you can space them in a bit with washers between the rails and wood. If your screws go into the T-nuts too far and make dimples on the outside of the carpet, you can use washers between the bolt head and the rails. This is a critical fit; get it right. Then tighten the bolts securely.
If this is a big, heavy cabinet that will sit on the floor, you may want to mount casters. If it is a smaller cabinet or must be stacked, consider heavy rubber feet on the bottom. In any event, your rack will be more durable if you install heavy plastic or metal cabinet corners with short wood screws. The box is then ready to use. If you wont be hauling your equipment around a lot, you can stop right here and start racking your stuff.
Otherwise, you may want to build and cover a front and back for the box. The simplest kind is a carpet-covered slab of wood that press-fits inside the lips of the cabinet, if you have the depth in front of any component knobs to do that. A better and more common solution is a shallow box-type affair that projects from the front and back and is secured with draw clasps, as shown in the photo of the grey box above. If your equipment projects flush with the rear of the main box, or close to it, a projecting back may have the added benefit of allowing various patch cords between the components to remain plugged in while things are being transported, or you can keep cables used for interconnection with other components right inside the rack case where they will be needed. One less thing to worry about at your next gig.
You have just completed your rack case, and Ill bet you spent a whole lot less than you would have at the music store, for something probably better-suited to your needs. Now you just need to rack up your equipment. If you have a heavy power amp, put it toward the bottom. Now with one of your extra spaces, put a ventilated blank panel above that. Your power amp generates a lot of heat, most of which is exhausted by its fan if it has one, but some of which radiates through the case. Id rather not have some other expensive and heat-sensitive component, carrying faint, line-level signals, mounted right above it.
Perforated "blank" panel positioned above heat-generating power amp. Top-mounted power strip allows the entire rack (in this case, amp and preamp) to be powered up at once, and the better ones filter the AC current.
Likewise, I usually put a multi-outlet, rackmount power strip in the top space and plug all the other stuff into that, so I can light up the whole rack with one switch. Those are usually very short front-to-back and AC adapters (wall warts) wont always fit if theres a deeper component mounted immediately below. Another good use for a blank plate.
Small AC adapter/transformers, or "wall warts," often project below or above a power strip and need clearance - either a less-deep component, or a blank plate below the strip.
By the way, there is nothing magic or unique about "rack screws." Music stores sell them in little bags for comparatively steep prices, but they are simply 10-32 thread, phillips-head screws about 3/4" long, and you can find their equivalent in most any hardware store at much cheaper bulk pricing.
Read a few eBay descriptions of used rackmount gear and you will see something like in great cosmetic condition except for some rack rash on the top and bottom of the case and around the mounting holes, from mounting in and out of racks. You can help preserve the tops and bottoms of your equipment by simply sliding them in and out carefully, preferably with the entire rack cabinet laid on its back so youre not fighting the tendency of the unmounted component to scrape against the top of the component below it. You can help preserve the screw holes on the front by using rack screws with little nylon washers on them, rather than bare screws.
Our little group has migrated to the point that most of our instrument-amp equipment, and all of our PA stuff, is rackmounted, much of it in homemade racks as described above. And we trade and swap components like baseball cards, trying this effects processor in that guitar rig, and that midi module in some other rack. If one component dies, we only have to substitute for its individual function and not the entire preamp-amp-effects combination as with an all-in-one amp head. Its convenient and flexible, and there are some fabulous-sounding instrument preamps out there that can be paired with an enormously powerful and clean power amp, for sound and power you just cant get in a conventional instrument amp head!
Publications by the same author: Design and Build Your Own Live - Sound Speakers - A book about How to build your own Pro-Audio Speaker systems - 117 pages of excellent information. ISBN 1-4120-2998-8.
Questions or Comments about this article? You can write Larry Mundy and in a rare sober moment he'll try to get back to you.
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