CB italian midget sub : lining up the hull halves

[raalst]

First mold is almost ready

First mold is almost ready now, just a bit of Flash to trim.

getting the rubber out of the plaster proved difficult because the
last layer of rubber didn't kick (enough) and therefore stuck to the plaster
(even after I applied talcum and petroleum jelly).

But thanks to my modelling skills ("if it doesn't work,
apply more brute force") and a large screwdriver I could pry the
two apart. The the rubber was peeled off the master and
put back in the plaster shell.

But the sticky mess on the outside of the rubber might
even prove handy, because some parts
of the mold stand vertical and might cave in without the mold sticking
to the plaster.



another learning experience was that the water from the plaster
caused the planking to warp. Not good. some isolation (cling
wrap, laquer or so) is required
when I make the next casing for the other half.

[raalst]

because I have motivation issues

because I have motivation issues with
doing a lot of things a second time for the other mold half,
I decided to try to get a hull out of the ready mold half.

that was good exercise.

I was worried the glass would refuse to follow sharp nicks and bends,
but this turned out te be not a problem at all.

I used 2 layers of gelcoat, and 2 layers of 80-grams weave
I tried thick mat in the bow, but that stuff does not bend so much,
and therefore requires small pieces

the green/blue patches are cotton, saturated in resin.
Tip from a german friend to negotiatiate sharp corners.

I also put saturated cotton in the tail.

but the weave was so forgiving I will not use cotton again.

so after a few hours I gave in and under the excuse that this was
just an exercise, I pulled the hull.


The weldlines (thread with woodglue) come out very nicely


one other learning point ]http://home.vianetworks.nl/~raalst/cb/dekgaten.jpg[/img]

well, back to the other half. now I know what I get in the end
the motivation is back.

[scott t]

Good work.

I am curious!
Could you

Good work.

I am curious!
Could you glass the sides of the boat and not saturate
the cloth for the deck? Then after the sides harden
rotate your mold so gravity works for you and finish
the deck.
Can you do glass work in partial steps and add to it later?

-Scott

[raalst]

that could work. But since

that could work. But since the saturation does stop gradually,
all cloth should already be hugging the mold.
so, the question is if I can have a sharp end of my cloth exactly in the
middle of that gap.

I already put the mold at an angle, but this did not help. I get the feeling
that the poly draws the silicone towards it somehow. Part of the problem is that the silicone is just too flimsy over there.

[raalst]

some small parts, made the

some small parts, made the easy way.



the white cylinder is the mold for a torpedo loading door.
The eggcups are the actual doors. The vaguely square parts are the hinges
of these doors.

I am very pleased with myself (gloat mode on) because of the following trick :
It is hard to get a thin-walled piece from such a mold. poly sags to form a puddle and the glass conspires with the lumps of gelcoat to create air
pockets. What to do ?
I put 2 layers of gelcoat into the mold (waiting inbetween for it to harden)
Then I put in strips of glass (not yet saturated with poly).After that the poly. no trick yet.

Now I took an old latex (?) glove from the bin, inserted a ball of paraffin
into the thumb. put this into the mold and pressed on the paraffin ball.
More balls until the mold was full. at this point the excess poly runs over the rim of the mold. all glass is pressured against the mold wall. Left this to harden out.
when the poly was hardened, the old glove was easily pulled loose. maybe a bit of paraffin needs to be scooped out first.

what is left is a nice thin-walled piece.

The other experiment is a piece of red play-doh. I pressed in the hinge-parts and filled the holes with excess poly. This was unplanned but worked well also. The play-doh gets sticky and dry but the poly comes out ok. a bit of sanding/filing/scraping to remove the left over play-doh and presto, hinges.
the only thing to remember is how to get the originals out of the play-doh, which explains the bits I glued to the original hinges.

[bigdave]

Some excellent ideas Ronald http://www.subcommittee.com/forum/icon_biggrin.gif

Some excellent ideas Ronald
I was thinking next time maybe try inserting a small balloon or a balloon made from the glove into the mold and pressurize it slightly with air. Just insert a short section of small model engine fuel tubing in the mouth and add a tie wrap to seal the balloon. Once the balloon is inflated just clamp off the end of the tubing. When it is hardened just release the pressure and pull the balloon out. I may work. BD.

[pirate]

Ronald,
Next time you need to

Ronald,
Next time you need to make more keys between your rubber mold and the hardback in a way that will hold the rubber to shape even when at an angle. I don't see really any keys on the deck side in your photos, though there may be some. Use different shapes for the keys, round and square, or even triangular, or rectangles with curved sides. Shapes that will grab and hold laterally to the surface of the hardback, but not going into it.

You could glass up to the edge of the deck, but coat with resin a little farther than the glass. Then once cured, rotate the mold and glass the top deck using gravity to help hold the soft mold in place. You may even want to experiment with lowering the amount of catalyst you're using. If you use too much, it causes too much heat which will cause the resin to lift from the mold. The trick here is to use enough to cure completely, but not too much to cause distortion, or lifting. Your ambient temperature while curing will affect this heat and speed of curing too. The idea is to get a slow cure. If the resin ends up a little tacky once it should have been cured, you already will have the correct shape, so you can apply a very thin layer of resin with more catalyst over the tacky parts to get it to cure completely and not be tacky without worrying too much about lifting. Just don't go overboard with the catalyst.

Then just overlap the glass at the seem between lay-ups. I've even frayed the glass on the edge where the separate pieces will meet to make a smoother transition. But since this is on the inside a sharp edge doesn't matter as long as the layers overlap. It's just like adding additional layers of glass after cure anyway. And you may want to rough up the first cured lay-up a little where they'll over lap to get a better bond. Especially if you're using a waxed resin.

Your work looks very nice though.

Pete

[raalst]

thanks for the tips Pete

thanks for the tips Pete !

I will have the possibility to do it all over again : the other side of the boat
has just been put into the parting board.
But doing it all over again is hardly worth reporting on.

I did not have kays, I had a rather rough surface because I mixed old
RTV snippets in, and figured that would do the trick.
But for some reason the last layer of (liquid) RTV never kicked off. so
the profile in effect became very worn out. Lego to the rescue
I'm sure making the RTV a bit thicker around the edge will also help.
i's simply too thin to carry the heavy lump of RTV near the edge of the mold.

PS : what is a waxed resin ?

[Guest]

Putting cured RTV into new

Putting cured RTV into new rubber can sometimes inhibit the cure of freshly mixed rubber. This especially the case with urethane rubbers.

Wax is put into gelcoat resins to form a top coat. Gelcoat resin is air inhibited, so it remains tacky on the upper surface, this helps it bond to the subsequent layers of resin and glass.

However if you want to use gelcoat resin as a top coat, sometimes referred to as a float coat, perhaps to finish off a hull, then you mix in a little wax with the resin.

This wax is lighter than the resin, so it floats to the top, and seals off the resin from the air, enabling the resin to fully cure, with no tacky surface.

You can buy resin with the wax already mixed in, this is usually sold as 'topcoat'

Andy

[pirate]

Ronald,
Actually, most standard polyester resins

Ronald,
Actually, most standard polyester resins out of a can (from home improvement, hardware and auto stores) are waxed resins. This is because most are sold as repair material for boats and cars. So usually one coat is all that is necessary.

The reason given is correct, it seals the surface off from air to help it cure completely. But the gel coats don't have wax so they can be easily backed up with regular resin, because it won't stand up to stresses without glass backing. The wax in resins makes subsequent coats not stick well to them. So if you're laminating with it, as we do to build up the thickness and strength of our parts, then you want a wax-free resin to use. Otherwise you NEED to sand that wax layer off between every layer applied in order for it to bind chemically.

You can then either use a waxed resin as your last top-coat layer, or, and this is even a good idea anyway, you can cover the last top-coat of resin with Seran wrap as tightly to it as possible to keep the air off and allow it to cure completely. The Seran won't stick to the resin and you can then peel it off when cured.

Pete

[raalst]

I like that SERAN wrap

I like that SERAN wrap idea.
It's also called cling-wrap, Right ?

after applying that film I can also put stuff in the hull to pressure it and squeeze out excess resin.

btw, I was at a regatta last weekend and somebody actually recognized
my hull-half as a CB !

[pirate]

Yes, cling-wrap—same thing. You can

Yes, cling-wrap—same thing. You can also use wax paper to squeeze out the excess resin. Where it puddles, I soak it up with paper towels even, but you have to take them out right away.

[raalst]

well, it took a while

well, it took a while but the first layer of silicone rubber is now slithering
off the second half of the plug.

thought I'd given up, did you ? HA !

You've seen all of it before, when I created the first mold.

photo's when I do something new, promised.

[raalst]

the second half mold is

the second half mold is ready !

from now on the adventure continues, i.e. doing all the moldmaking
a second time was quite uninspiring...
but from now on it's interesting again!!



the sagging deck problem of the first mold half has been fixed in mold 2 with a stout lump of rubber, that bit won't cave in in a hurry.

[anonymous]

Ronald I have missed your

Ronald I have missed your progress and I'm glad to see you are on the way to having your boat. Well done sir! Not easy to do.

Steve