Time for an update. I've got a little more work done on this. SeaHorse Fanatic has a similar project going built by a friend of his. This is what provided the motivation for me to finally get started on a LED fixture for my system.
http://www.canreef.com/vbulletin/showthread.php?t=81619
I checked out the local machine shop for aluminum stock that mseepman recommended, but they only had larger, thick material & I'm looking to keep the mass & weight of my build to a minimum. They recommended I try another local machine shop, but I was on my way to Kelowna that day anyhow, so went to Princess Auto where I had scored some reasonably priced square & angle stock before. Ended up getting some thin 8 foot lengths of 3/4 aluminum angle for about $15 ea incl taxes.
I haven't made up any kind of plan on paper or otherwise, kind of doing it on the fly. Still waiting for heatsinks, power supply & additional LEDs I've ordered, customs is taking their time in processing the shipments. grr. Since I have the aluminum & hardware to get started, I put together one 4 foot rack with two heatsinks.
Had some thicker angle stock left over from building my MH/T5 rack, so used those pieces at each end of the lighter stock. Threaded with 8-32 tap & used stainless bolts to fasten.
Here's a detail view of the business side of the heatsinks with 10 watt LED arrays loosely positioned. Will endeavour to keep the wiring neat & tidy, using small terminals or soldering wires together & covering with heatshrink tubing. I'm thinking heatshrink will provide protection from moisture, but we'll see.
Here's the flip side of the rack, showing the fans on the heatsinks. This will be facing away from the water surface. I threaded the heatsinks to allow use of stainless bolts for fastening. Tried 6-32, but one didn't hold, so went with 8-32 here as well. Mounted the heatsinks diagonally since this provides the best clearance for the fans to do their job of cooling. They're plenty secure with two 8-32 ss bolts.
Spacing from center of one heatsink to the next is approx. 6 & 1/2 inches. This will allow installation of at least 6 arrays equally spaced along the 4 foot rail. I'll start with that, or maybe 5, & see how that goes. The thing I like about using this material & fastening with bolts, is that if I need to modify the set up, it's as simple as drilling additional holes. Electrical hookup should also be easy to modify, with a minimum of soldering. Also still thinking I might add a few MR16 bulbs to the rail as needed. This will allow me to spotlight a certain coral or area of live rock with a custom LED colour of whatever works for that area. Just need to figure out a way to fasten the MR16 bulb socket to the rail. Shouldn't be too difficult.
I'm thinking 3 of these rails for my 4 foot tank. One down the center & two along the outside. Not quite sure whether I'll hang them or make up something to set them on the tank rim. Either way, I plan to install the outside rails so that they can be swiveled to point slightly inwards. A single bolt through the end brackets with a wing nut to allow friction fit with quick adjustment should do the trick.