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[funtimefrankie]

Was delivering to firm today and they were busy vac forming (jelly moulds as it happens) but asking the boss he said he could do one off jobs if supplied with the master, which could be made from wood. His jelly mould masters were aluminium for heat reasons but for just a few wood is OK.
So if anyone wants any vacforming done they are in Skelmersdale, near Wigan in the wondeful North West of England

[DavieTait]

Provided the hull shape isn't too complicated its possible to do most styles including submarines ( Steve Neil has done a batch of RC Subs using his own vac-former )

[barriew]

In the MMI publication about building boats from plastic card by Ricky Web there are some "instructions" for do it yourself vac forming.

Barrie

[tigertiger]

I worked in a plastics factory for a short spell.

The forms/moulds were made out of wood and then covered with car body filler.

All of the moulds were positive. As in they were the shape of the finished product (a bit like a plug), the outside shape. So if you were forming a hull you would have to allow for the thickness of material if you were strict about scale. But allow for the base material to stretch thin where most formed.
So a 6mm bath is made froma 6mm thick sheet of perspex/acrylic, but the bottom of the bath is opaque it is so thin, hence rienforcing with FGlass.

The use of a positive mould may have been related to the material used. We mostly used acrylics, but sometimes used ABS.

[kiwi]

Hi,
I worked in a factory making chest freezers for a while and the liners (in 6mm ABS) started (obviously) in a fat sheet and where first blown upwards, to stretch the plastic, then vacuum applied and the plastic sucked down into the female mold. This helped retain a more uniform thickness over the whole liner. The inside of the liner you see in the chest freezer (or upright fridge) is the side away from the mould to minimise any imperfections from the mould on the finished visible surface. Our moulds where wooden.
The whole machine had been made in-house from wood and aluminium and looked very 'jerry-built' but did the job.
I'm sure hull moulds could be successfully moulded in a similar way, but to include hull detail from the female mould.

regards
Kiwi

[tigertiger]

After Kiwi's post I realise I did not explain too well.

Where I worked, the baths were done in a female mould, the showertrays and other componenets used a male mould.

But both male and female are posetive forms. They are the exact same form as the finished item and not an inverse (negative) of the finished item. So a convex former/mould for a convex product, a concave form for a concave product.

Another key thing is that the visible surface is the part that is away from the mould, as Kiwi noted. If memory serves, plastic sheet has a good/face side, this is always placed away from the mould face.

So for hull forms the moulds should be male. Any 'basins/wells' in the deck should be achieved using a female form.
E.G. the swimming pool in your 1:20 scale QE2

[Martin (Admin)]

I've built a couple of boats that were obviously made from female / negative moulds ( Graupner Fiat Uno, Robbe Comtesse, Robbe Scarab 38 ) and these were miles better to the normal vac formed male moulds. The corners and spray rails were far sharper.

Yes, female moulds are a lot more work and difficult to make  but the end results are far superior.
Martin.

[portside II]

Ha you have just put a smile on our lasses face and the words "i told you we are better" in my ear
daz

[tigertiger]

Here are some pics.
Pics 2-4 are courtesy of Roman Pecks MJW build.


Pic 1, you can see the hull form, and you can just make out the 3 piece keel set up. You would need to modify the arrangement.
But the hull has a squared off edge along the keel line. Glueing the wood with epoxy was easy.


Pic 2. you can see the straight section keel and stern post arrangement.
Pic 3. you can see where the pre-cut curved stem piece fits.


Pic 4. shows the inside of the hull, giving an idea of what the plug would have been like.


I am pretty sure this was a male mould.

[nemesis]

Hi, Use ABS when forming, if you have a cockup you can reheat and reuse the ABS, something you cannot do with styrene. Also lots of companies are blowmoulding now. Vacforming is 14lb air preesure whereas blowmoulding can use a lot more than that, hence the external detail is much better. Nemesis