boatgeek
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I've teased a couple of pictures on this project. Now that it;s a little further along, I'll start up a build thread.
It all started with a 4' long 6" diameter mailing tube that the sales guy at Rockler fished out of a dumpster and gave to me. It wasn't really long enough for anything but a stubby, and I don't really have room for a 6" diameter 3/4FNC rocket, so it gathered dust in the garage for a long time. I'd wanted to build a tubefin for a while, but again, it would be too big. So I compromised, in the spirit of @neil_w 's ring fins and @Dotini 's plexiglass not-quite-tube fins. And that gave us Project Venn:
29mm motor mount, 2.6" LPR tubing for the body, 6" ID rings that are just tangent to the body tube, and a little bit of shaping to the fins to give them a little style. Oh, and while I was at it, I threw a carbon fiber wrap on the outsides of the fins. It probably wasn't strictly speaking necessary, but it looks nice and the final result will be absolutely bulletproof. As you might imagine, marking and cutting this was an exciting job. This is where my copy of Rhino for work came in...
It's pretty straightforward in Rhino to intersect surfaces, so I made an inside and outside for each tube, marked a constant elevation and the intersections, and unrolled it into a flat surface. And since the cuts where the tubes intersect aren't square, there's a template for the inside and the outside. It all fit on a single 11x17 sheet, so I could print it off on a relatively normal printer instead of a big plotter. The templates were in two pieces, but they weren't hard to tape together. The little square up above is a 1010 rail, so I'm confident that it will slide nicely on to the rail.
Here's two of the rings cut and nested together, plus the process of marking ring #3:
I marked the outside with Sharpie since it didn't bleed too much over the epoxy. I marked the insides with a pencil since that showed up nicely on the cardboard. Each slot had a cut at the mating line plus two more rectangular windows that I could use to mark lines that I'd join up into full cut lines for the egg crate. This way, the pattern stayed nice and sturdy through marking all three fins. I also marked the center of the pattern so that I could line up the inner and outer patterns. One fin had four bottom cuts, one had four tops, and the last had half and half. Marking the last one was an exercise in measuring five times and cutting once. All cuts were made with a Dremel tool and cutoff wheel.
And this is what it looks like now. I am honestly shocked at how well it fits. The motor mount will have upper and lower centering rings just catching the tops and bottoms of the rings, so it should be nice and sturdy.
Next steps:
Drill recesses for rail buttons into one ring fin where it would touch the body tube
Coat the inside of the rings with epoxy
Paint the rings except right in way of the glue lines
Glue the fin can together, make nice fillets where the rings meet
Paint the body tube except in way of glue lines (?, maybe this should be later?)
Glue the fin can to the body tube
Insert the motor mount (and probably a piece of coupler to stiffen the body tube just above the fins)
Touch up paint
It all started with a 4' long 6" diameter mailing tube that the sales guy at Rockler fished out of a dumpster and gave to me. It wasn't really long enough for anything but a stubby, and I don't really have room for a 6" diameter 3/4FNC rocket, so it gathered dust in the garage for a long time. I'd wanted to build a tubefin for a while, but again, it would be too big. So I compromised, in the spirit of @neil_w 's ring fins and @Dotini 's plexiglass not-quite-tube fins. And that gave us Project Venn:
29mm motor mount, 2.6" LPR tubing for the body, 6" ID rings that are just tangent to the body tube, and a little bit of shaping to the fins to give them a little style. Oh, and while I was at it, I threw a carbon fiber wrap on the outsides of the fins. It probably wasn't strictly speaking necessary, but it looks nice and the final result will be absolutely bulletproof. As you might imagine, marking and cutting this was an exciting job. This is where my copy of Rhino for work came in...
It's pretty straightforward in Rhino to intersect surfaces, so I made an inside and outside for each tube, marked a constant elevation and the intersections, and unrolled it into a flat surface. And since the cuts where the tubes intersect aren't square, there's a template for the inside and the outside. It all fit on a single 11x17 sheet, so I could print it off on a relatively normal printer instead of a big plotter. The templates were in two pieces, but they weren't hard to tape together. The little square up above is a 1010 rail, so I'm confident that it will slide nicely on to the rail.
Here's two of the rings cut and nested together, plus the process of marking ring #3:
I marked the outside with Sharpie since it didn't bleed too much over the epoxy. I marked the insides with a pencil since that showed up nicely on the cardboard. Each slot had a cut at the mating line plus two more rectangular windows that I could use to mark lines that I'd join up into full cut lines for the egg crate. This way, the pattern stayed nice and sturdy through marking all three fins. I also marked the center of the pattern so that I could line up the inner and outer patterns. One fin had four bottom cuts, one had four tops, and the last had half and half. Marking the last one was an exercise in measuring five times and cutting once. All cuts were made with a Dremel tool and cutoff wheel.
And this is what it looks like now. I am honestly shocked at how well it fits. The motor mount will have upper and lower centering rings just catching the tops and bottoms of the rings, so it should be nice and sturdy.
Next steps:
Drill recesses for rail buttons into one ring fin where it would touch the body tube
Coat the inside of the rings with epoxy
Paint the rings except right in way of the glue lines
Glue the fin can together, make nice fillets where the rings meet
Paint the body tube except in way of glue lines (?, maybe this should be later?)
Glue the fin can to the body tube
Insert the motor mount (and probably a piece of coupler to stiffen the body tube just above the fins)
Touch up paint
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