CB italian midget sub : lining up the hull halves

[raalst]

Thanks for the kudo's !

Thanks for the kudo's !

Gantu, maybe this link is of interest to you.
I found it at the www.betasom.it forum.
It is about the british chariots, and has a few detail
photo's.

http://www.hdsitalia.com/articoli/29_chariots.pdf

[raalst]

I have to reproduce small

I have to reproduce small recesses for sliding bolts in the superstructure.

I want to have these structures in the mold, I do not want to add them afterwards.

I found a quick way to create these funny shapes

- drill large hole
- fill with (wait for it..) filler
- push in a small negative form I made
- after hardening, wiggle out the form
- sand the displaced filler down

[raalst]

Slowly but surely the build

Slowly but surely the build continues.
I am making a mold for the tower.
This is a bit over the top, but it is an exercise
for the big hull.

The tower will eventually be made from polyester.




and just to fool you about my sloth-like speed of building ]http://home.vianetworks.nl/~raalst/cb/halvemal.jpg[/img]

M3 nuts make great registration bumps.

[raalst]

"My first poly".

how do

"My first poly".

how do you guys battle bubbles in the poly ?
my form is riddled with them.
I did first apply a coat of poly without glass in the
mold, but the stuff is just too runny to make a
decent thickness. and the glass has a mind of it's own. after thumping it in place, after a quarter of an hour it appears to have wrestled loose again, creating a "nice" pocket of air.

[Guest]

You need to apply gelcoat

You need to apply gelcoat before using lay up resin.

Gelcoat contains a thixiotropic additive which makes it thick, and prevents sags and runs.

It is also air inhibited, which means the surface exposed to the air remains tacky. This helps it bond to the layers of resin and glassfibre.

When I lay up a mould I use the following-

1. One coat of gelcoat, brushed into the mould
2. Once that has cured to a point where it's tacky but firm, brush lay-up resin in and a coat of glass surfacing tissue, then lay two layers of 300 gram CSM. Saturate well with resin, then I consolidate with a washer roller.

Job done. No air bubbles.

Andy

[raalst]

second try got out better

second try got out better :



This is model building glacial style.
But hey, it's progress just the same.
As soon as work gets back to it's usual dullness,
the hobby will pick up speed again.

Ps ]http://www.subcommittee.com/forum/icon_redface.gif[/img]

@ andy :
I am curious how much time passes when putting
on all those layers. Do you do a layer a day ? or just
everything in one go (apart from the gelcoat-getting-sticky wait) ?
And, how is the yellow submarine getting along ?

[Guest]

I've been working on the

I've been working on the yellow submarine today.

I added a keel at the bottom a week or so ago, made a moulding board and I've decided to scribe in some panel lines, then I'll cast, probably do this tomorrow- good fibreglassing weather at the moment.

Regarding fibreglassing time span. I tend to mix up some gelcoat, apply this in the morning, say 9-10am, by midday it's tacked off nicely.

I then cut up my pieces of glass tissue and CSM and lay them next to the mould. Mix up some resin apply, to the mould add glass, stipple in more resin to fully wet it out, consolidate with a roller, add more glass, resin etc.

I don't add any more than two layers of 300 gram matt and perhaps one layer of tissue in one application, else I find it can get a bit unmanageable.

This is enough reinforcement for a smaller model (i.e. up to a metre or so)

I find the limiting factor is the pot life of the resin- it can kick-off awfully fast in hot weather, so I like to work with smaller quantities to avoid wastage.

The main thing to avoid is leaving too much time between the gelcoat and fibreglass stage.

If this is too long, then the gelcoat loses it's tackiness to some degree and then it won't bond well with subsequent layers of resin and glass.

If you do leave it for a while, then rough up the gelcoat a bit with some wet and dry sandpaper to provide some tooth for the resin to latch onto.

Andy

[raalst]

ok, but from this i

ok, but from this i conclude the glass layers go in directly/shortly after each other ? whole job done
in one day ?

[Guest]

Yes that's right. Takes me

Yes that's right. Takes me about two hours or so which includes a big break in between to allow for the gelcoat to harden.

You should then leave the lay-up in the mould for a couple of days at least for it to cure off- polyester keeps moving, unlike epoxy which is a more stable compound (you pay dearly for that however). Some folk recommend leaving the lay-up for a couple of weeks, but I get impatient after a few days, and to be honest I haven't had any problems with warping to date. However I'm only doing small castings at the moment.

I know one chap who does lot of GRP laminates in polyester, and he pulls the castings after a few hours, with no ill effects that I have witnessed (he builds very nice models).

Andy

[raalst]

A bit of progress this

A bit of progress this week :

I made some plating from lead slab.
The form I needed was almost impossible to get right (and symmetrical)
but in the end it did turn out not too bad.



The "bolts" are pressed into the lead slab from behind with a
makeshift tool. it is an allen nut (at least that is what I beleive you call them)
and a bit of hexagonal brass rod. with this I made a sort of prong.
insert lead, apply hammer, presto.



the original plating can (just) be seen in this photo ]http://home.vianetworks.nl/~raalst/cb/cbwa/DSCN0261.JPG[/img]

[raalst]

I sort of finished the

I sort of finished the deck details today, at least to a level
where I would like to make a mold from it.



still a lot of welding lines to go...

[raalst]

I researched the weldlines from

I researched the weldlines from the photo's I made.
what a patchwork !
current idea is to simulate the weldlines by thread, soaked in glue.

[raalst]

Making weld lines from thread

Making weld lines from thread and thick white woodglue.
The white ones are fresh, the glue shrinks a bit and gets
transparant when dry.





Because of the scale and the hurry in assembling the originals
the weldlines must be crude on the model as well.

Hope it looks OK when the felt tip marker "artwork" is painted over.

Since I make a mold of this thing, such construction methods are
possible. It would never hold on the final model.

[Guest]

I've had PVA 'rivets' on

I've had PVA 'rivets' on my Seehund for 10 years with no problems.

The other stuff I've played with regarding weld lines, is cyano gel.

Works well- I picked the tip up from the Delta construction PDF on Norbert Bruggen's website.

Andy

[raalst]

I made preparations for taking

I made preparations for taking a mold.

I used PUR to prevent the boat wobbling while making the mold.
very quick and easy.

The board is movable, so I can line it up exactly with the boat.

The thick part of the tail will be sculpted onto the hull with plasticine.
This was the safest way because I did not trust myself with that tail being
part of the total assembly. It would have broken off as soon as I tried to move the boat.

5Kg of silicone rubber is waiting, at the expense of 132 euro's (ouch!)