Conical plastic cone for BT60?

[EXPjawa]

Does anyone know of a source of a plastic nose cone to fit a BT60 tube that is straight conical in shape (ie not parabolic, elliptical or ogive), and around 3G exposed length? I know that there are some balsa options, but all of my experience with using balsa for a cone with a needle-like point suggests that it'll break before it ever flies. I guess I could have something 3D printed, but would prefer to find an off-the-shelf part if possible...

 

[Gary Byrum]

HERE

 

[Bat-mite]

And HERE.

 

[EXPjawa]

I appreciate the suggestion, but I don't see any plastic cones at BMS (at least not in the size that I'm looking for).

Gary, I assume that you're referring to the 38mm cone, correct? Will that fit a BT60 tube - my understanding is that the OD is larger and the ID is a bit smaller. Apogee also has fiberglass cones for 38mm tube, but again, it doesn't seem like a good fit to the tube I'm using.

 

[neil_w]

That PML cone is also *solid* and 130g. Zoinks.

 

[Gary Byrum]

Gary, I assume that you're referring to the 38mm cone, correct? Will that fit a BT60 tube - my understanding is that the OD is larger and the ID is a bit smaller. Apogee also has fiberglass cones for 38mm tube, but again, it doesn't seem like a good fit to the tube I'm using.

Oops, my big bodda bad! eRockets has one though.

 

[neil_w]

OP requested plastic. If neither eRockets nor BMS has it, then I'm going to go out on a limb and say that it doesn't exist.

 

[EXPjawa]

I used that cone on my Black Brant III build. But its balsa, and as I noted before, is quite damage prone. Part of the reason that I wrapped it with aluminum foil tape was that it needed reinforcement, and it had already been repaired. It helped that the rocket in question also was to that an aluminum-look on the cone anyway. But for this inquiry, I'm specifically looking for something plastic.

 

[kjohnson]

Well... there's the cone for the new Nike Smoke kit, or the old scud cone (PNC-60B) but not much else.
kj

 

[Marc_G]

I suggest if a plastic one doesn't exist, get the balsa one and thoroughly saturate the front part of it with thin CA. Then coat the rest of it to harden. The tip will be nearly as resilient as plastic.

 

[EXPjawa]

Marc, I appreciate the input, but in my experience that's not really the case. That is, in fact, what I've been doing right along - and what I did for the Black Brant III referenced above. The CA will harden the balsa, and that does make it more dent/ding resistant and easier to finish, but it remains brittle. The CA does nothing to improve the toughness or resilience of the wood, and the glue itself is fairly brittle. It can still break easily in a shock impact in a way that molded plastic will not. As noted before, I've still broken the tip off of every thin-section balsa cone, treated with CA or not. So, I'm looking for a better solution. As it is, even CA soaked tips are likely to break if the rocket is knocked or blown off a table onto the floor/ground. Harking back to another recent thread, I wonder if wood hardener would impart better toughness than the CA does, but the hardener would have to have good impact-resistant properties.

 

[GlenP]

Cardstock over a styrofoam cone, maybe? If you are concerned about the tip breaking upon landing, could you rig up a chute line to the middle of the cone so it falls on the shoulder first, kind of like how a Mercury Redstone is rigged so that it does not fall on the tower.

 

[neil_w]

Yet another suggestion: if you can find a smaller plastic cone with the same aspect ratio, hack off the tip of the wooden cone and replace it with the tip of the plastic cont. Yes, you'll have to do a good job gluing it but if your primary objective is to strengthen the point then maybe that would do it.

 

[Gary Byrum]

Now I have to wonder what kind of surface you're landing on. Even a hard surface can wreak havoc on a plastic cone. Not as bad, mind you. But if you're breaking balsa nose cones that much, maybe you can get one turned out of bass wood or even something unusual, like oak. It seems obvious at this point, that you're not going to find a plastic one. Too bad too. I prolly wouldn't mind getting my hands on a conical that size also.

 

[EXPjawa]

The landings are typically on a farm field, which can range from hard dirt to soft foliage, etc. That's not really the issue. The actual issue is general durability in handling. Where I've had these break was in transport, or when the wind knocked it off of my table, or when I accidentally knocked it over on the shelf. The sort of stupid stuff that ought to be avoidable but happens anyway, and that a plastic cone would be a lot more forgiving of.

Thanks all that had input. I was hoping there'd be something I was unaware of, or in a kit I could pirate. One thing I'm considering is similar to Neil's suggestion, and have 3D tips made that can be appended to balsa or maybe act as a tip cover.

 

[K'Tesh]

There's always kcespedes' shop on Shapeways, but he's not cheap.

 

[EXPjawa]

Oh, I checked that too, but they don't list anything similar either.

 

[Marc_G]

@EXPjawa,

Thanks for taking the time to explain further. I see your need, and feel your pain as I do have some tip-broken cones myself.

I've used the Minwax wood hardener, but in my experience it won't give the kind of strength you are looking for. And it takes a long time to fully outgas (like, weeks) particularly if you've really soaked a cone with it.

What about taking some polystyrene (say, that crumbly white foam often used as shaped cushions in device shipping boxes) and dissolving it in whatever solvent is most appropriate (maybe acetone or chloroform), creating a good amount of dissolved plastic, then soaking the cone in that? Then let it dry, tip down? So you'd wind up with a cone thoroughly saturated with the same plastic that PNCs are made with, reinforced by the wood fibers.

Just a thought. I'm following this thread with interest. Please keep us posted.

Marc

PS:For what it's worth, I did my own search for molded plastic cones per your description, and came up empty. I did like the idea above to create a hybrid cone using a plastic tip! Sort of like some of those machbuster rockets with the aluminum nose tips.

 

[Kruegon]

I am not aware of a plastic cone to meet your needs. But have you considered a soak in wood hardener as a way to make it more resilient?

 

[gpoehlein]

It would be even heavier, but you could always have Gordie at Roachworks/Excelsior turn a balsa cone with a hardwood tip that you would glue on. Or just have him turn the whole thing in a harder wood than balsa. If you hollowed it out somewhat it wouldn't be quite so heavy.

Another alternative would be to have someone 3D print one. There are three downsides to that:
1) Most hobby printers don't have the print volume to make a BBII nose in BT-60 (mine only prints 5"x5"x6" - a common size).
2) a lot of hobby printers only print in PLA, which can't be easily vapor smoothed like ABS, and sanding PLA smooth is a royal pain!
3) PLA doesn't take heat well, and if you leave your rocket in a hot car, your cone will not likely be straight any more.

One other option might be to roll a cardstock cone, fill with expanding foam for strength and then coat the surface with CA. If you aren't good with sharp cardstock tips (I've been doing cardstock for 10 years and most of mine still don't turn out perfect), you could make a transition that goes most of the way to the tip, cut the fill foam smooth and glue the tip from an Estes or 3D printed cone to it.

Certainly, none of these is as easy as a molded plastic cone, but all should be more durable against incidental dings than a balsa cone.

 

[Tonimus]

I may be way out in left field here, but what about painting the balsa with wood glue? Or dipping it like a candle in wood glue?

 

[Gary Byrum]

This may or may not be up your alley, but I had to do this last night. I dropped a big balsa nose cone on the concrete patio and dinged the tip pretty good. Rebuilding it was my only option, so I drilled a small hole in the top of the ding, stuffed it with epoxy putty and built the rest of the missing portion up larger than I needed with more epoxy putty. Today, I'll grind/sand it to shape. This is something you might consider because it will reinforce the tip, making it less likely to break. You'll be adding a little weight there, but not that much. Just food for thought. I'll let you see how that went when I finish it later today.

 

[EXPjawa]

I am not aware of a plastic cone to meet your needs. But have you considered a soak in wood hardener as a way to make it more resilient?

I may be way out in left field here, but what about painting the balsa with wood glue? Or dipping it like a candle in wood glue?

As it is, even CA soaked tips are likely to break if the rocket is knocked or blown off a table onto the floor/ground. Harking back to another recent thread, I wonder if wood hardener would impart better toughness than the CA does, but the hardener would have to have good impact-resistant properties.

I think that wood hardener has better potential than wood glue; any type of treatment of the balsa would have to penetrate the wood well, and would have to good resilience to getting smacked around. Simply coating the surface only essentially "case hardens" the wood, but doesn't change the core properties. It'll help it shrug off minor bumps or fin impacts, but wouldn't offer any protection from the sort of shear loads that have broken tips in the past.

I am curious to see if Gary's epoxy method works out. Having Gord make a hardwood tipped cone is another option; I've certainly had several cones made by him. My concern with either is that the stress will simply move to the tip joint, and the break will occur there. That might not be the case, but the break point usually moves to where the stress is most concentrated...

 

[Gary Byrum]

I think it worked really well. Requires some craftsmanship to get it shaped. I'm not done with this one though. The tip gets rounded off and I was in the middle of repairing other damage. Once I get the primer on, I'll prolly find some areas that need some Bondo attention. Much tougher than the original tip too.