Scratch built tubes?

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Gunkie

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I've done a fair amount of fiberglassing on-top of existing stock tubing for HPRs. What I'm considering doing is building custom fiberglass tubing for a full-custom, two-stage (K-to-J), scale model taken from Rockets of the World (Allway).

My question is: How do I remove the paper form from the cured fiberglass?

I'm worried about using a release agent (i.e. Vaseline) that might gum up the inner part of the tube. This would probably lead to some structural weaknesses. Any ideas?

Thanks!
 

rocwizard

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Throw the part you make into a pool, like on the aurora and Big Daddy rockets. Thy formed the tubes around quik-tubes and then tossed them in a swimming pool, and they pulled right out

HTH
 

daveyfire

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What Eric said... go swimming with the tube.

To make the release even easier, wrap the tube in 2-3 layers of longitudinal strips of heavy duty 3M packing tape (the brown stuff). Then either spray on a PTFE release agent (easy to apply, harder to find), or wax the tube with 5-6 layers of Carnauba wax (longer to apply, builds up forearm strength :p). When you're done, and after you've gone swimming, stick a sharpened dowel down in between the tube and the composite layup. Work the dowel around, then pull the tube off. Voila!

And keep us posted on the construction!
 

Gunkie

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Smart ideas! As a surfer, I have plenty of warm (hard) surf wax around and have plenty of experience applying it. The packing tape idea is unreal! That's exactly what I was looking for and it makes perfect sense.

Grad school is quickly coming to an end, and other than some contract work for a local microelectronics firm, I'll be filling my hours trying to build this rocket. I hope to:

1. Learn how to use a lathe to produce custom hardwood nose cones and transitions.
2. Make custom airframes.
3. Sew my own parachutes.
4. Possibly build my own electronics for staging and dual recovery deployment on both stages.

But, if I get a real job ;)


Thanks again!
 

daveyfire

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Oh, but the fun doesn't end there... use composites and a female/male mold layup and a vacuum bag system to make the nose cone lightweight and strong (carbon fiber anyone?) and then do the fins the same way and get the exact scale shape with vacuum bagging and and and... :D

Keep us posted Scott!
 

cls

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daveyfire, can you expand a bit on the female/male mold system? building a tube and matching nose cone sounds great!!


and, anyone have any ideas for a good way to build a mandrel of an arbitrary size, so I can build tubes of any size?


muuuuhuuuwaahahahahah! I might not leave the garage this winter!
 

daveyfire

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WELL...

first you make the tube. After you have the tube made, trimmed, and pulled off the mandrel, you can start work on the nose cone. Basically, the idea is to make a "positive" of the part you want by the easiest means possible, then make a "negative" mold over this, then pull out more "positive" parts until you have enough. It's how PML does their nose cones.

What you need first is the plug. Turned wood would make a fine plug, as would metal, or another plastic nose cone of similar size. It needs to have a polishable, non-porous surface to which you can apply release wax. Wax it down with 5-6 layers of Carnauba wax, letting each one set 30-40 minutes and then buffing it off before applying more. An alternate to this is PTFE release agent like I mentioned above. Once you've done this, you need a way to support the plug so half its surface is exposed. One way to do this for a nose cone is to build a box with depth 1/2 the diameter of the cone, and cut out so the nose cone fits inside. Set the part in the box, and put pieces of glass starting on one side of the box, across the nose cone, and down to the other side, so you end up with about a 2" wide "shell" on either end of the nose cone form in the middle of the mold. You should make the mold ~3x as thick as the part to be pulled from it, for structural reasons.

The next part is to pull another mold half off the plug/box. You need two halves of the mold to make a whole :). After you have both sides, the rest is easy. Cut out pieces of cloth (fiberglass, carbon, Kevlar, whatever) to fit the shape of the inside of the mold. Put more release wax inside the mold, and laminate the inside of the mold with the thickness of cloth you decided on before, however many layers. Apply them all at once and you can do a vacuum bag job on the half.

When that's all done, just pull the molded halves of nose cone out of the molds, and laminate them together with strips of glass down the inside. Fill and sand the seam, and voila! Custom nose cone complete.

It's not that hard, I swear! ;)


Pictures 'n stuff, and a better description than I can provide at John Coker's site: https://www.jcrocket.com/nike-asp.shtml#nosecone


Hope that helps!
 
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