Easy Flexy Rack

When I began searching the web for a DIY audio rack, one design kept popping up, the Flexy Rack. The low cost and relatively easy construction, combined with reasonable attractiveness explains its popularity. Here are some of the links I found useful: TNT, Audio Tweaks, Salamander Designs Archetype. I've built my rack and I think it turned out pretty well. Based on my experience, I've got some advice to share. (You probably were wondering why I'm writing yet another Flexy page.) Here's the executive summary. Use an inner tube and a drill to spin down the nuts MDF should be painted to prevent outgassing of formaldehyde The 5/8" threaded rod is beefy enough, and Finding 3/4" threaded rod and accessories is really tough Four posts are more stable than three Don't make it taller than your chin Use bent mending plates for production-line painting

Introduction

I pretty much ignored the manufacturers' suggestions for cooling space above components. I don't live in an oven and I don't play stuff too loud. I performed some multi-hour heat experiments and decided on the vertical clearances above.

From the above, I determined that my shelves would need to be 19" x 18" exclusive of supporting hardware. This is larger than normal in the depth, but my five-channel amp is quite deep. It's not that critical, though, if one looks at where on the amp the feet are mounted.

The big conclusion was vertical. I would need nine shelves, of 3/4" thick MDF (medium density fiberboard). The shelves alone work out to 6 3/4". The components and cooling space contribute 43" and 14". Adding in 3 1/4" for top and bottom hardware and feet, I came up with 5'7" threaded rods. Luckily the local Orchard Supply Hardware carried 5/8" all-thread in 6' lengths.

The Shelves

Plywood, particle board and MDF are all held together with urea-formaldehyde resin glue. This is the same formaldehyde that the United States Environmental Protection Agency considers a "probable human carcinogen". There is some debate about the severity of outgassing from furniture products, but I decided not to take the risk.

To seal the shelves, I applied wiping varnish to all six surfaces of each shelf. Be warned that the sawn edges of MDF are sponge-like in their ability to absorb varnish. My original plan was to leave the shelves in their natural varnished color, but the results were blotchy. The varnishing was greatly facilitated by spacers which let me stack the wet shelves. The spacers are merely "mending plates" from OSH that I bent into porcupines. I placed three under each shelf in a sort of tripod. The tiny pin-prick marks in the finish are barely noticeable. Another helpful hint is to use latex exam gloves during these messy procedures.

The post-varnish shelves were safe, but looked like puke. So, I decided to paint them. The quickest, easiest, and best looking color I could think of was black. I bought a can of Rust-oleum semi-gloss black paint at OSH. Applied with a mini-roller, this worked great in a single coat. I think the varnish undercoat helped. Again, I used the spikey spacers and gloves to make the job easy, painting all six surfaces in one session. I found a foam brush worked well for the edges both painting and varnishing.

The final step in preparing the shelves was drilling the corner holes. The size of the neoprene washers dictated that the holes be centered one inch from each edge. I used an 11/16" spade bit for the holes in order to allow a little play. I think this was the right call. Since I own a drill press and a shop vac, the drilling was a pleasure. I built a positioning fixture and clamped the shop vac hose right to it. All 36 holes were completed in about 15 minutes. It took longer to build the fixture. As you can see, the holes came out cleanly. I think they would have been troublesome had I painted after drilling. On the assembled rack, nobody can tell, and the washers probably seal in the gases well enough. If you don't own a drill press, you should build a jig. It will take longer than with the press and you'll have to be careful, but the end result should be just as good. Just remember to back-up the holes with scrapwood to avoid tear-out.

Rods and Ends

The basic plan is to sandwich each shelf corner with washers and nuts. For nine shelves, that's 72 nuts, steel washers and neoprene washers. Along with the 6' 5/8-11 all-thread, I got the nuts and "cut washers" at OSH. The neoprene washers were harder to find. I looked online, but in the end, I ended up at the local Home Depot. In the nuts-and-bolts aisle, in the special-stuff drawers, they sell 5/8" x 2" x 1/16" neoprene washers for $0.58 each. They usually stock 3, so I had to talk to the Crown Bolt representative for a special order. People differ on the importance of the neoprene washers. I'm not sure but figured I'd play it safe. At the very least, I think they make the tightening easy and discourage the nuts from working loose. For the top, I bought some cheesy black plastic end caps. for the bottom, I bought some rubber tips like would go on the end of a cane. The threaded rods need to be cut cleanly and uniformly to length. Measure twice and cut once. Some people use hacksaws, but I really enjoyed using my 4 1/2" angle grinder with an abraisive cut-off wheel. The cuts were clean and easy.

Assembly

At this point, the "kit" was basically complete. One needs only a few additional items: a 12" bicycle inner tube, a variable-speed reversible drill, a crescent wrench, a measuring tape, a torpedo level, and some Blu Tack. The major complaint most people have when assembling this type of rack is that spinning down the nuts is slow and fatiguing, especially if one forgets a washer someplace. I think I've solved this problem by using "belt drive" to turn the nuts. I started by cutting the inner tube as shown. I discarded the inside loop, leaving a sort of rubber belt. Then I washed the powder off. This leaves the belt for the belt drive. If powder remains, turn it inside-out. To start the actual assembly, it's useful to have a flat, level spot. I achieved this with a slab of plywood and some shims. I used lots of shims because the rack is pretty heavy.

For me, the trickiest part was the first part: attaching the bottom shelf. This involved getting all four threaded rods poked through the corner holes. I put on the bottom set of neoprene washers, cut washers and nuts, leaving about 1 1/4" of threaded rod to accept the rubber tips later. I did all this with the rods horizontal. The next step was to turn the rickety unit vertical. This position made it easy to put on washers and nuts. Here's where the belt-drive method comes into play. I first put the "belt" over the drill chuck. Then, I placed the other end over the nut. I used one hand to steady the rod while using the other hand to operate the drill. It took a little practice and could be awkward with a heavy drill, but I was able to spin a nut five feet in about fifteen seconds.

As I added the shelves and nuts, I followed a simple order:

Black to black
Washer to washer
Metal to metal
Nut then nut

When done, I put the end caps on top and the rubber tips on the bottom. One idea I liked was to fill each rubber tip with a chickpea-sized gob of Blu Tack for improved damping.

Conclusion

I put some teflon-like furniture glides under the rubber feet so I have a fighting chance of moving the rack. It still takes major effort. Now I'm trying to find the proper rack/tv/speaker/subwoofer configuration without getting a hernia.

Basically, I think the rack turned out pretty well considering the relatively low cost and quick construction. The color scheme (black and silver) is pretty forgiving, too. As far as height, mine's too tall. If I ever actually wanted to use my turntable, it would be inconvenient.

Thu Jun 17 16:07:38 2004