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Old Apr 17, 2012, 03:28 AM
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casting hulls

im up at night tonight and decided i will try something ive been tossing around in my head for a long time. casting hulls from a plastic female out of paper mache. paper mache was once the CF of its day.

at any rate, i am curious as to how far i can take this old medium. (and my wife loves the news paper so i got waaaaaay to much just lying around were ever she tosses it!)


edit: pics. empty hull, first layer and final layer
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Old Apr 17, 2012, 04:55 AM
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Elmhurst, NY (Queens in NYC)
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Hmm...

Home depot sells this foam in a spray can. I wonder if you could just shoot foam into the hull to make a replica?

If that works then adding a balsa structure with blocks to make things like servo holes might also work.

Now if only someone made a hull like what I want for the sailboat I've had in the back of my mind for months!

Pete
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Old Apr 18, 2012, 11:10 AM
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ive heared of people doing that. if this comes out okay, i will make a positive lould and work from that. this one is pretty much proof of concept. ive been trying to mould things for a while now and paper mache seems like a decnt medium to work with, assuming i can fuel and water proof it.
if thsi works, the possiblites are endless. what worries me is the strungth and rigity of the hull. i am thinking of addiing some thin CF rods and changing the starch adhesive recipe to include something a little stronger.
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Old Apr 18, 2012, 03:28 PM
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Add watered down Elmers glue to the mix. criss cross the paper layers for added strength too. even newspaper has a grain to it. I like this idea. gonna wait and see how you make out. Please keep us posted. Subscribed...
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Old Apr 18, 2012, 11:10 PM
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i did criss cros. the hull is out of the mold now. a few things, a fiar ammount of shrinkage (expected). the hull s some what narrower than the origonal. i pulled it out too soon and the aft end was not dry and some of the bottom hull.
its pretty strong, some twist in it but very stable on the long axis. there is a lot that can be done with this, seeing as i can cast strength or flex in to a shape.
i will see about getting some paint on her and some pics and some laquer for it.

i evne had the thought of casting a WTC.... depends on how well the hull reacts to water. i will know more later.
still some variable to pin down.
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Old Apr 21, 2012, 08:10 PM
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it works! sort of. the i sealed the inside and outside then filled it up with water. it held water for a long time, but softened the hull. i did not seal the inside as well as the out side, the test was the seal on the inside of the hull. (think really big cup)
anyways, it was rushed aswell. the laquer need some time to harded even after it drys, i did not let it. time to make another hull!
im gonna try a more presice method this time.
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Old Apr 23, 2012, 01:38 AM
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There is a glue sold called Weldbond. A fellow in the local club makes similar hulls using it and thin crepe paper. He uses it to reinforce thin hulls and seal them, same as one would use fibreglass.

Might be worth trying.
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Old Apr 23, 2012, 04:13 PM
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that is a good idea. i will have to look into it.

got the hull positive seperated, i built it on glass, and it was hard to pull off! i had to break the galss. (next time i will use SS, single strength glass, 1/16)

starting the laquer the mould. just setup paypal for in-store payment, now its off to home depot to see if it work!

EDIT: got some titiebpond III, water proof glue. and i just reailzed a few things.
1 there was no shrinkage on the positive hull. odd, cuz there was some on the negitive, i think. now im not sure.
2 the positive is not right, the upper hull came out poor.
at this point, i am thinking of making a plaster of paris mould of the origonal hull , then using that as my main mold. not sure how muc plaster i have left, or how long the plaster mold will last. ugh.

pics of the positive uploaded
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Old Apr 24, 2012, 03:07 PM
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hull #2

started the second hull. i realized i had shrinkage when making a negitive, but not the positive hull.
the one is 2.5 layers, the last layer was mostly reinforcement and not a complete covering. using waterproof titebond glue. its not rated for submerged, but i will psray the out and inside with laquer for waterproofness.

now we wait for the hull to dry. the yuma heat should help things a bit. i will give it two days.
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Old Apr 29, 2012, 04:00 PM
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is there a way you could use epoxy as the glue? regular 30 minute epoxy gets fairly stiff, and is water and fuel proof. wipe down the plastic with some Vaseline to help release it (it may not adhere to the plastic but better to be safe)
looks interesting and has lots of potential, if you used the female mold, you could add formers inside the hull that would make it all one piece and add strength.
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Old Apr 30, 2012, 04:32 PM
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30 min? nevefr thought of that. the hull i made failed, took too long to dry, and now i have to get the glue and paper off the female. but an epoxy might work. do exopys need o2 or dry/cure?
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Old May 02, 2012, 10:31 PM
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they will cure on their own, thats why it can be used in a vacuum bag
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Old May 03, 2012, 12:28 AM
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any ideas of some very thin runny stuff or how to make it?
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Old May 03, 2012, 04:11 PM
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i added high percentage alcohol to some regular 2 part building epoxy, it can take longer to dry, but it still works. i try not to mix it more than equal alcohol to epoxy, i think 1/3 alcohol is a good mix.
i heard others claim its not good, but i haven't seen any ill effects, and the wing i bagged with it is plenty strong.
the alcohol is cheap at walgreens, 91% is about $1.75
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Old May 06, 2012, 08:44 PM
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Thunder Bay Ontario Canada
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I have had great results by putting the components in the microwave for about 20 seconds. The hot components come out like water and set up very quickly as opposed to using at room temp. Be careful with the microwaving process though. Make sure the bottles are open and don't put them in for too long or the bottles will melt and leak - ask me how I know.

P.S. if the microwave method scares you then you could always place the component bottles in hot or boiling water. Again make sure bottles are open and don't overdo it.

Good luck
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