CB italian midget sub : lining up the hull halves

[raalst]

a peek at phase 2

a peek at phase 2 "the disease progresses"

I bought me this miracle :



this is a complete Linux computer including usb, wifi, memory card reader
and ethernet. about the size of a finger.
With the wifi antenna up in the periscope it will provide me with depth data
at first, then sonar and video.

having said that I slip back into the comfy straightjacket these big men in white coats are offering me

bought at www.gumstix.com, all in all about 300 euro's (because of tax and shipping). But for that price it will keep me entertained a long while.

[raalst]

It took me a year

It took me a year but I'm now glassing the hull.

I think I will need a few tries to get it right, it looks like foam instead of glass.

[raalst]

I just pried loose the

I just pried loose the first hull half.
it looks usable.

@ mold/scratchbuilders : how do you go about sanding/sawing/filing the hull halves until
they match ? Do you glue the sandpaper to a table and move the hull ? a very long
plank covered with sandpaper ? beltsander ? the thing is 120cm, the joint should be
flat...

and another : do you coat the inside of the hull with anything ?
or is plain poly good enough ?

[bigdave]

I have one of the

I have one of the very flat laminated balsa building boards that I tack glue sandpaper too with 3M-77. Then I move the hull back and forth over the sandpaper. Make sure you have a good line marked on the hull to sand too. Try to apply equal pressure and check your progress often.
This works for me. BD.

[PaulC]

Ronald,

This info is way past

Ronald,

This info is way past its useful life for you on this particular layup but what I do is trim the excess cloth from the mold prior to the complete cure of the part.

When the layup has reached the point where it is starting to harden but is still not too solid -- the consistency of thick chewing gum is a good way to describe it -- take a razor blade and slice off the excess along the rim of the mold. If the weave feathers along the cut, or pulls in the mold, it is not hard enough. Keep waiting (if you have to saw with the blade you've waited too long).

You'll know when the time is right. The blade will slice through the laminate like thick butter and leave a clean edge right along the face of the mold. This allows you to have a nearly perfect matching surface when using a two part hull mold.

This is my favorite part of the process. The sweaty, stinky labor is done and you have a part that is neat and trimmed. All it takes is cure time at that point. Once the cured parts are popped out of the mold a quick check against each other will reveal any spots that need a touch of sanding.

My Type XXI lower hull is laid up in two halves like this then the two molds are bolted together and the halves are laminated at the seam. That beats trying to glue two loose hull halves together.

Sorry I couldn't have passed this along sooner! And thanks to Matt Thor for the original tip when I was starting out.

[raalst]

thanks for the tips.
I

thanks for the tips.
I have never encountered the "rubber" phase, but maybe I make another pull
(if only to build experience..). I gave up on the deck. I will make that separately.

but for now : she is born !

[tmsmalley]

Congratulations to the proud papa!

Congratulations to the proud papa!

[Guest]

Looks nice Ron. I guess

Looks nice Ron. I guess you could make a separate mould for the deck, or perhaps lay-up some glass and resin on a waxed flat piece of board, and cut the deck from that.

[raalst]

a few "lessons learned" on

a few "lessons learned" on all of this :

- your poly hull (and mold) should not have lots of details that have to match up.
I have some warping, and several weld lines do not line up.
had I done these after molding, that would not be a problem.

- keep the form of the hull as simple and smooth as possible.
I added a bit of the superstructure and a tail. This was done because I wanted a
sturdy tail and a clear place where to put the superstructure.
but the tail warps, and the superstructure does not line up.
also, these details create sharp corners, which are difficult to follow with glass mats.

- avoid sharp corners
I could have left off the keel, avoiding several sharp corners. then I could have
poured a separate keel later

- only use the master-mold-hull appaoach when you want several hulls. otherwise it
is simply not worth the trouble (and delay..)

I am considering to use the master, peel the weldlines and other detail
from it and put poly on it in order to try out the straight master->hull approach.
just to compare.

anyway, with this hull I have now, I will proceed to put left and right together.
maybe an inner rib will help lining up the two halves.
one half seems to be less tall than the other, so some force is required...

[raalst]

to keep you entertained :

to keep you entertained : how I glued the bow halves together.

Both halves are a bit warped but I need to line up the weld lines.
what to do ?

I drilled small holes next to each other, in each hull halve. insert steel wire
and turn the ends of the steel wire. this gave a solid fit, with which I could now
continue with the polyester.

Due to my ineptness both hull halves vary a lot in thickness along the bow.
And I learned that that means air pockets when applying
the glass mat.
So, I mixed the poly, then added loose 5mm strands (I have a bag full of that stuff) until the mix was fairly dry.
This mix was put in the bow and thumped into submission with a paintbrush.
Then I covered the whole inside of the bow (I had the hull positioned under an angle so the bow was level) with an old plastic bag (a ziploc bag where the glass cloth had been sold in). on the bag some sand to distribute the pressure, and on that a large flagstone.

The result was a smooth and solid layer of poly in the bow.

I had the outside of the bow taped off, so the surplus resin has filled the gaps between the hull halves nicely

I'll now be working my way back to the tail, getting the hull halves to match...




<edit> gravel in the ziploc bag also works nicely to compress the poly.

[raalst]

I'm busy making the rudders,

I'm busy making the rudders, which is quite a job.

but in the mean time I have been experimenting with a
3D-printing shop, a service that can create parts
designed on the computer in plastic.

the periscope top 4cm, 1.5 inch and a coverplate 1.2 cm, 0.5 inch
for a diveplane axle
came out like this :



it is tough stuff, but sandable and paintable. glue-tests
commencing..

I used http://www.shapeways.com as the printing service.

[raalst]

it is made in their

it is made in their cheapest material, called Strong white & flexible (SWF)
i suspect it to be some sort of Nylon.

it is very tough and not that flexible. even with a file it is hard to make a dent. It takes paint no problem, CA glue does work, only the plastruct type of welding cement does not bite it. I have to try epoxy glue still.

I like the result very much. Next step : my own gear pump and custom bayonet rings (and an improved step sail, I now have the drawings of the originals. have a look at the "ships plans" section under Guppy 1b).