Just your basic 3" rocket with twelve 18mm motor mounts. Made with mailing tube and an Aqua-Pod water bottle as a nose cone.
The basic components are six 'stiffy' 18mm tubes from Uncle Mike's, a 3" mailing tube with telescoping inner tube from the Container Store, an Aqua-Pod water bottle from Safeway, and plywood from Michaels.
I started by cutting the stiff 18mm tubes in half. I then glued them together in one set of four, one set of two and two sets of three before stacking the subsets. I used Tightbond Trim and molding glue, which was a mistake. Even though these are quite stiff they reacted poorly to the water based glue and the whole assembly warped like crazy. Luckily, I checked on it before going to bed and found that inserting motors in both ends of all the tubes forced it back into place. Whew.
The tube assembly was then mounted in a 3" coupler (i.e. a chunk of the inner mailing tube). To allow the tube cluster to fit, I had to trim about 1/8" off the 6 tubes that abutted the coupler. This was easy with a diamond cut-off wheel on my Dremel clone. To plug the outer 9 tubes, I cut plugs from corrugated cardboard, coated them with wood glue and then glued them in. I mixed half an ounce of epoxy filler to cap the cardboard plugs and fill all the gaps.
I cut three fins in sort of a Standard ARM motif. The roots were angled to fit in the gaps between the motor tubes and were attached using a custom fin alignment jig. The fin assembly is held in the mailing tube with the lower rail button and a plastic pop-rivet from Giant Leap.
Since I thought the rocket had a lower than normal probability of success and I'm generally scrounger, I decided to make the nose from an Aqua-Pod water bottle. I've used several of these in various ways and had one left. I filled the bottle with 2-part foam and mounted it in another piece of 'coupler tubing'. I finished the upper section with another piece of mailing tube, custom-cut plywood bulkhead, and an eye bolt.
I added a short piece of coupler stock ~1/2 way into the body. This provided an attachment point for the upper rail button and the through-the-wall shock cord mount.
That was about it. I soon gravitated towards a faux-scale look as shown in the as-finished photos. I contemplated what to stick on the end of the Aqua-Pod and settled on a plastic body from a do-it-yourself termite trap that I liberated from a neighbor.
I flew the 12-pack at MDRA's ESL-145 using three Estes C6-7s for ejection and nine Quest 'long burn' C6's along for the ride. Ignition was handled with Quick Match. The flight was great - nice and smokey! Ejection was a bit early but recovery was nominal. Peter 'shaken not stirred' Abresch snagged a good video of the flight. (Even though the linked video identifies the motors as D12s, they really were C6s!)
This is the biggest cluster I've tried and it worked out well. I am pleased with the final look, even with the non-traditional components.