Triple Vee

Yup, that is exactly the plan, virtually word for word. Prior to gluing, I'll sand bevels 30° off of facing surfaces of the fins using another jig. For gluing the pairs and then sanding in the convex curve I'll use the same jig that later holds the fin pairs to the tube for gluing them to the tube. That is, the jig has room for all three pairs, and I can use it for one pair at a time while assembling the fin pair subassemblies. The root edge rounding will be done with sand paper wrapped around a coupler.

Paper or finish the fins prior to attachment?

I usually fill and sand prior to assembly, and hadn't thought to do otherwise. Maybe it's time I gave papering another try. (I tried it once for strength, which means with glue not labels. I didn't wipe the glue off thoroughly enough and ended up throwing the fins away. Then since I had to make new ones I used basswood and didn't feel like I needed the paper. One of them split on a hard landing - repairable and long since repaired - and I'll never know if papering the basswood would have made any difference.)

I wouldn't think these fins have any particular unique strength requirements, should be able to use whatever technique suits you.

Indeed. I just figure maybe I'll try it your way for once and see how it goes. Or maybe I'd be better off saving that for a simpler design.

Label paper should be totally OK here, just leave a little exposed area at the root on one side of each fin where the two fins will glue together. Those are simple trapezoidal fin shapes with all straight edges, which is the dominant factor in how difficult the papering job is. Well, that and how many edges are rounded.

Well, I tried to enlarge the fins and managed to brake RockSim. See this post.

jqavins said:

Well, I tried to enlarge the fins and managed to brake RockSim. See this post.

Click to expand...

Is it just an issue with the 3D rendering? Do the side and end views still look ok?

Nope, the 2Ds are just as screwed up. If it were only the 3D I'd have a little bit of confidence in the sim.

This project is not dead.

I'm traveling tomorrow for Thanksgiving at my sister-in-law's. Her husband (who used to be my roommate) has his lathe all set up and working, so I'll be turning the nose cone. I haven't got back to figuring out what wen't wrong with the fins in RS, and life is slowing down getting back to it. It will happen.

Ttempted the turning of the nose cone. While I've dome turning small wood turnings on machine lathes before, hardwoods and pine alike, it wurns out balsa is too soft and weak, at least without more adapting of techniques that we did. The block We attempted it with is ruined. So I now have to decide which of several Plans B I will employ. Opinions and suggestions are welcome, but may not be followed.

I'm not very experienced with lathes, but what type of tool were you using? I wonder if something like a fine rasp or even sandpaper would work for turning balsa.

That might help. I certainly would have finished with sand paper, because the cuts were very ragged even before it failed altogether.

The actual faiure was that it wouldn't stay on the center and in the chuck. I have a ,ethod in mind thatmight help with that. But I don't often have acces to a lathe to try it on.

Would you glue hardwood to the ends of the balsa for the lathe to hold on? Wood turning is definitely a skill that I would love to have the opportunity to practice.

A club member who does these things well likes to insert a wood dowel in the end of the balsa (real wood, not stuff that gets cut with a fingernail ) and grabs it in his drill press or lathe for sandpaper shaping.

Without a drill press or lathe, you can strap a hand drill to your bench and tape the trigger down

I glued & screwed a plywood disc on the base of the one I experimented with.

One possibility is to attach hardwood end caps, as suggested. Another is to insert wood screws centered on each end. On one end go only as deep as the threads, cut off the head, and grip the shoulder in the three jaw chuck. On the other end, sink the screw all the way, be sure it's phillips or socket head, and place the (live) center in it. Another is to get a couple of the metal pieces that real wood turners use on the ends of their work pieces.

All of these are dependent on having access to a working lathe again, which happens only once in a while.

Another option is to pay someone who routinely does balsa turning to make it for me. Another possibility is to find off the shelf transitions and a cone to build up the overall shape. And finally, I could 3D print the sucker.

I'm not sure which part of this needs to be made out of solid balsa... looks like a conic nose cone followed by some cardstock transition work. Of course, Gordy could turn a piece like this pretty easily for you, but if you want to fabricate it yourself then there are ways.

I never think of cardstock shrouds, becaise it's not a method I've ever used. Turn it, piecemeal it, and 3D print it are simply the only things I thought of. Turning seemed the easiest of those at first, but clearly it's not as easy as I expected.

Now I have a fourth option to consider.

Here's the thing: cardstock shrouds of relatively normal size and shape (such as those in your design) are incredibly easy to make... once you've had a bit of practice. The good news is that practice is quick and costs nothing but some cardstock. It is an extremely useful skill to develop.

I did most of my shrouds in 65 lb cardstock because that's what I could find; subsequently I found some 110 lb stock at Walmart and I like it much better.

Your biggest challenge there is the close proximity of the shrouds to the nose cone... the interior structure there will take a bit of creativity but nothing too difficult.

If you want any specific technique advice on shroud making I'll be happy to tell you what works for me, but there has been plenty written on shroud technique already.

Joe, your post reminded me that I have a small lathe sitting in the basement. It didn't work, but now it does, so I'm curious to try making something with it from balsa.

I agree with neil_w, though, you could probably come up with something from cardstock, centering rings, and tubes.

jqavins said:

...and tangent to the BT-60 body tube at the aft ring, the rings 50 mm apart. I got only about 3½°. So I might want to go up to BT-80 and/or push the rings closer together.

Click to expand...

Joe, did you end up deciding on BT-60 or BT-80?

jqavins said:

Ttempted the turning of the nose cone. While I've dome turning small wood turnings on machine lathes before, hardwoods and pine alike, it wurns out balsa is too soft and weak, at least without more adapting of techniques that we did. The block We attempted it with is ruined. So I now have to decide which of several Plans B I will employ. Opinions and suggestions are welcome, but may not be followed.

Click to expand...

Joe, I just turned a nosecone for a Kraken I built out of 38mm BlueTube. I didn't have any balsa around my shop so I used some tight grained cedar ( a 4x4 cutoff ). I used my Grizzly metal lathe. I screwed a metal disk to one end to chuck it up. I then used my metal lathe tool to turn a 3/4" shoulder on the outside end that fit snuggly into the 38mm tube. I unchucked the wood, took the metal disk off, and shortened up the piece on my mitersaw to get rid of the screw holes. I then cut a 3/4" length of blue tube to go over the shoulder to protect it when I chuck up that end.

I used my turning tools from my wood lathe for the rest of the turning. Softwoods definitely require a light touch. I got it down to close and then used various grits of cloth-backed sandpaper to get it down the rest of the way. Pardon the pun, but it turned out pretty good.

Greg Furtman said:

Pardon the pun, but it turned out pretty good.

Click to expand...

Yeah, that looks great, have you flown the Kraken yet? What size motor mount did you use?

mbeels said:

Yeah, that looks great, have you flown the Kraken yet? What size motor mount did you use?

Click to expand...

Martin, I used a 24mm motor mount with an Estes screw on plastic motor retainer. I plan on using Aerotech E30-7 motors. I found a Kraken Rocksim file online, opened it up in OpenRocket, made mods to the materials, and the sim with the E30-7 puts it at around 1400'.

I was taking very light cuts. I never even got the block down to round before it failed, mostly because I made the mistake of mounting the balsa directly, four jaw chuck at one end and live center at the other. I'm sure it would have worked fine with cedar or basswood, not that better mounting wouldn't have still been a better idea.

Marten, if you like I'll send the dimensions when I can turn on my computer at home; the power's been out since Sunday night thanks to a snow storm. It's BT-80. Thanks very much, and please send me the bill.

Joe, I took your image from post #4, and scaled and printed it for BT-80. Is that still the same nose cone design that you're using?

jqavins said:

...the power's been out since Sunday night thanks to a snow storm.

Click to expand...

Hopefully you get power restored soon. Does your water come from a well pump, or do you have a municipal source for water?

Not exactly. It's the right idea, but was a quick Visio sketch, not the current RS design.

We are on our own well. Which is going to suck if the power doesn't come back on today. But it may be back on by now for all I know.

Joe, got power? I hope so.

Here's a pic of the Kraken nosecone I made right after taking it off my lathe. You can see the BT around the shoulder. And notice the nice tight grain of the cedar.

That's lovely.

Power came back late in the afternoon yesterday, so about 42 hours. I didn't get to the computer.