Introduction: Cable Control for a Pull-out Shelf

Like most folks, nearly all of my electronics and computer gear--well, the stuff on shelves anyway--was stacked on a shelf with the wires gently shoved behind everything. When anything failed--and something always did--it was nearly always the piece of equipment on the bottom of the shelf. This precipitated the usual round of trying to balance all the other equipment with one hand while unplugging and untangling the cables from the back with the other hand. And also invariably, I'd pull half the cables either out of the wrong component or out of the back of unit they were sitting in.

When I finally got to the point where I could have a [relatively] custom office, I decided that none of the computer equipment was going to suffer from that any more. Components were going to be only one deep on each shelf and i was going to manage the cables so that they were organized and I could get in and out of the cabinet with ease.

Which was easier said than done...

The shelf part was easy; I'd just make sure I had enough shelves and make sure they were installed with pullouts. The cable part was another matter; and in fact the pullout made the cable part more urgent. Just sitting components on shelves and allowing cables to dangle meant that I was probably going to crimp, crease, score, slice or otherwise screw up all of my cabling. I'd seen several cable management arms for rack-mounted equpment; however, they were both way too wide (for your typical 3/4" shelf) and way too expensive (for your typical cheap nerd: me). After lots of design experimentation I finally came up with the piece here.

Incidentally, this is my first attempt at an instructable (please be gentle with me :-). And I apologize in advance for the quality of the photos. I tried to take them one handed so that you can see me manipulating the pieces; however, I'm not particularly steady when I do that. All of those photos look like a cross between earthquake pictures and something from the movie Cloverfield (and have been--mercifully--left out).

Step 1: Get Set Up

The first thing to do is gather materials and take appropriate measurements. My control arm dimensions are based on two important measurements: the depth of the cabinet and the thickness of the shelf. I'll deal with the second one first.

My shelves were 3/4" particle board with a front trim edge for strength and to make a more attractive edge. So I'm using aluminum C channel that has an interior width of 3/4". Honestly, an exterior width of 3/4" would be better, but my local big-box home improvement store doesn't have that. And with a thickness of 1/16", it really isn't that far off (more on the thickness issue momentarily). I also used two pieces of aluminum 1/16" bar stock--3/8" and 1 1/2"--that I'll cut down for connectors.

The depth of the cabinet decided the length of the stock; my cabinet is 24" deep (actually, more like 23.5"). Therefore, each part of the arm needs to be close to 12" long so that when the shelf is fully extended, the arm isn't overextended (check out the diagram for a little more clarity). Given the number of these I was planning on building (3 shelves worth), I needed 6' of C channel. For the bar stock, I only needed about 1' of the 3/8" stock and about 2' of the 2" stock.

Regarding the connections, the unit itself is connected using 1/8" pop rivets--8 of them per arm. The arm is connected to the pull out shelf using two #8 machine screws and nuts (1 1/4" length). The other end of the arm is connected to the back wall by 4 #6 5/8" wood screws; however, you can use whatever length is appropriate given the wall you're attaching to.

Regarding tools, you'll need something to cut down and shape parts of the aluminum stock. I used a right-hand and left-hand set of tin snips and a bench grinder, but you can do all of it with only a bench grinder. You'll also need a drill with an 1/8" drill bit as well as a hacksaw (or some other tool to cut the aluminum stock) and a center punch and a hammer. And the pop rivet gun, of course.

What about the 1/16" issue? Well, thicker (1/8") would be better but it would make fabrication more difficult. The necessary strength is really dependent upon how much weight the arm has to bear and how often you plan on moving the arm. So if you need a really strong arm, thicker stock would be better ... or using a different metal (like steel). In my case, neither was an option (couldn't get the aluminum thicker and the steel was just too expensive). So far, these have held up well.

OK, let's get started.

Step 2: Make the Arm

The next thing to do is fabricate the arms.

For each drawer, you'll need two arms. In my case, they're all 12" long to start. Cut them with your favorite tool of destruction (in my case, a hacksaw). You don't need to be too neat here as you're about to change all the shapes with a grinder anyway.

Once you've got your arms cut to length, you'll need to cut down and reshape the ends. The first cut is to remove some (about 1") of the center stock to allow for cable movement when the arm articulates. The easiest way (for me, at least) was to cut along the sides of the C channel with right-hand and left-hand tin snips (to get right up against the sides). Once that's cut, it's a simple matter to bend the excess material until it snaps at the fold (don't worry about the rough edge; it'll get ground down when you trim it up with a grinder).

The next step is to round the ends where the arms meet the connection pieces. They need to move cleanly and rounding them makes for easy movement of the hinge joint. You can get fancy here and create a template for rounding, but drawing it freehand works just as well. Also, if you want save yourself a little time and effort, take your tin snips and cut the corners off before you finish rounding with the grinder. I found that using the tin snips first makes the final rounding much, much faster.

The last thing you'll need to do is drill the holes for the pop rivets where the connectors will be attached. Because our C channel is 3/4" on the inside dimension, it'll fit perfectly over a piece of scrap 1" stock. With the C channel mated up with a piece of scrap, use the center punch to position 4 holes for the connectors. Once these are riveted into place, they'll serve as the articulation points for the arm. Drill the holes out with the 1/8" bit.

Step 3: Make the Connectors

The next thing to do is to fabricate our connectors.

We have two types of connectors we'll have to make: an "elbow" hinge to connect each arm, and a "wrist" and "shoulder" hinge to mount to the shelf and back wall respectively. We'll start with the elbow ...

For each cable guide you build, you'll need two elbow pieces fabricated. For the dimensions I used, check the associated pictures. Given that I was using 1/16" stock, it was pretty easy to cut each one just using the tin snips. Once the blank was cut, use the tin snips again to ease the corners. And then finish the corners using the bench grinder (you'll probably need to use gloves or a pair of vise-grips while grinding; the pieces will get pretty hot from the grinder). Once each piece is finished with shaping, you'll need drill two 1/8" holes for the rivets in each. Again, use a center punch to get the drill started in the right place (I found that lining all the elbow pieces up together, clamping them into a vise, and then drilling them all at once, was the most effecient and the least likely to screw one up).

Finally, we'll need to fabricate the wrist and shoulder pieces. Conveniently, they're cut from the same pattern. The only difference is one is bent at a right angle for the wall mount. The process here is pretty much the same as for the elbow: cut the blanks, trim them with tin snips, grind them to final shape, tap a drilling guide, and clamp in a vise and drill. Once that's done, take two of the blanks and place them--lined up--in the vise right at the fold line. Then slowly bend one piece down into a right angle (using the vise as a guide) and the other piece into a right angle in the opposite direction (again, using the fise as a guide).

And with that, all of our pieces are fabricated. It's time for assembly!

Step 4: Piece Them Together

Next, we'll attach everything.

Start by taking two of the arms and the two "elbow" connectors. Making sure that the two C channel arms are back to back, pop rivet one of the elbow connectors to each of the arms. Flip the assembly over and then pop rivet the other elbow to the bottom of the set of arms.

At this point you may notice a couple of things. First, lining up the holes may not be exact; particularly if you drilled the holes the way I did (by eyeballing them). As long as you're close, it shouldn't make a difference; the arm will still articulate ... it will just have a little more friction. The second thing is that the elbow hinge doesn't move uniformly. Don't worry about this yet. Once the rest of the assembly is done, connected, and installed, the movement will be uniform.

Next up, take two of the "wrist" pieces (the flat ones), and pop rivet them the same way you just did the elbows (to the top and bottom respectively of one of the arms). Then take two of the "shoulder" pieces (the folded ones), and pop rivet them to the only holes left in the arms.

The last piece is strictly optional. I had some adhesive zip tie mounts that were 3/4" across. They fit perfectly into the channel and would allow me to make sure the cables stayed within the channel. The two drawbacks to this were that they were adhesive (which would come loose eventually) and that they took up about 1/8" of the base of the channel. A better solution would be to cut slots in the arms to hold velcro ties but, honestly, I was too lazy to do it. Maybe next time.

Step 5: Mount the Arm and Start Using It

Finally, we'll attach the arm and wire everything up.

Before attaching the arm, it's a very good idea to do a test fit. You want to know that the arm--when the shelf is closed--won't hit the shelf tracks or the back of the cabinet. You also want to know that the arm is long enough to not pull loose when the shelf is all the way out. If there's a problem, now's the time to know about it. Note that you can have the arm articulate from either the left or the right by flipping it upside down. In my case, I needed the arm attached on the right side of the cabinet and the shelf because of where the cables were entering in the back. Your mileage may vary.

BEFORE YOU START: take a moment and check what wires and cables you're threading through there. You've got an opening in the arm that's at most 3/4" x 1". If your cables won't fit--because the fittings on the ends are too big or there are too many of them--you'll have to take all of this apart to fit the cables through before attaching them again. For example, if you've got a VGA cable going through there (like I had), it will not fit through that hole. In this case, I had to thread them all through in advance before I bolted the arm down. You've been warned.

ALSO BEFORE YOU START: if you took the route I did and added those zip tie mounts, take a few minutes and pre thread the zip ties through the appropriate holes. As you'll quickly discover, they're hard enough to get in there when the arm isn't mounted. Doing that while hunched over, half in the cabinet, with your arms nearly over your head will cause you to exercise your considerable four-letter vocabulary (if you don't have a considerable four-letter vocabulary, contact me ... I seem to have some to spare).

OK, test fit is done and everything fits. It's easiest to start by mounting the arm to the shelf. Find the position of the arm on the shelf and, with a bit slightly larger than 1/8" (large enough for a #8 machine screw), drill completely through the shelf at the two mounting holes. Next, with the #8 machine screws and nuts, fit each screw through the top mounting hole of the arm, the shelf, and the bottom mounting hole of the arm. Attach the the nut to the bottom and tighten. Repeat with the other screw and nut. At this point you may notice that getting these things fit in here requires a bit of twisting, shoving, and holding your head at just the right angle. Depending on how accurate you were in drilling all those holes, this part will be either very easy or the most difficult part of the whole effort.

Next, with the drawer in the closed position, take two of your small wood screws and mount the top-most of the "shoulder" hinges. Once that's firmly mounted, pull the drawer back out--to give you better access to the bottom mount--and attach it. My cabinet had thin enough material in the back that I didn't need to drill pilot holes. Again, your mileage may vary.

The last thing to do is attach your cables. This is an exercise in trying to satisfy conflicting goals. You want enough cable so that when the arm is fully closed the cables aren't pulled too sharply around the elbow corner. However, you don't want so much that when the drawer is open that the cables have too much of a bend at the hinge (see the diagrams to see what I mean). This will also be complicated if you've got cables that have to be sized from two different ends. For example, some of the cables I was attaching couldn't have much extra slack on the drawer side, so I should attempt to tie that side down first. Some of the other cables couldn't have much slack on the back wall attachment, meaning that I should probably tie them down first. What worked for me was to tie all of them down, but not to cinch the zip ties in snug. Then I could work the individual cables to where I needed them cinching the zip ties down once everything was satisfactory.

One last thing that you'll probably note from the pictures. I had more cables than would fit into the arm mount. Specifically, I had the power cable for the drawer that I needed to tie down. I found that the easiest thing to do was to use velcro ties to tie that cable to the top of the arm. Obviously, this will work for any type of cable if you've got too many cables to fit in the arm.

Step 6: Final Thoughts

Nothing is perfect, and neither is this arm. Given that, what would I do differently?

First, I'd probably spend a little more time dressing up the edges I did with the bench grinder. They won't cut the cables, but I could make them look a little better.

Second, I'd probably run a wire brush over the entire arm. Again, it doesn't affect the function, but it makes it look a little better.

Third, I'd look into a way to tie the cables down without using the zip tie mounts. As I said earlier, the adhesive is eventually going to come loose. And they take up a little more room in the arm than I'd like.

Fourth, I'll listen to the suggestions that I'm sure to get from you readers. I'm certain that I haven't thought of everything here. As I mentioned at the start; beefing this thing up certainly wouldn't hurt, but I'm too cheap to custom order heavier C channel (to say nothing about how this would affect the ability to use pop rivets for the hinge points). And there's got to be plenty of other things y'all will think of.

Nonetheless, thanks for reading. I hope this works for some of you!