Male or Female

[clive]

I had always assumed that you would start off with making a Plug and then take a fibreglass mould which would become your female mould for making your fibreglass submarine. From one or two well explained buildups featured on this site it read as if people were going to lay fibreglass over the 'Plug' and using the resulting fibreglass object as their submarine. Is this so or am I being a stupid old pensioner

[himszy]

I can only recall Dan's

I can only recall Dan's SF Storm that does it that way as he used lost foam method....All the others (IIRC) do fibreglass the plugs yes, but that to make them stronger as opposed to them being the actual hull.

Which one(s) you looking at?

Michael

[paul von braun]

Clive, you have described, perfectly,

Clive, you have described, perfectly, the 'correct' method of glass lay up.
What one does is make a male mould first - this must be perfect in its detail, since all imperfections will be transfered to the female mould.
The next step is to paint some release agent (usually pva based if I remember correctly) onto the male mould followed by the 'gel coat.' The gel coat may have some coloured pigment added to it if so desired. Then comes the lay up proper - with either chopped mat or woven cloth.
When this is cured, the male mould is removed from the female.
The process is repeated, but within the female mould - the final 'moulding' is then removed from the female mould. If everything has gone okay, then the moulding should be a perfect copy of the male mould you made at the begining!

Paul.

[Guest]

Clive,

Invest some of your pension

Clive,

Invest some of your pension in this book-

http://www.amazon.co.uk/Glass-fibre-Han ... 0852428200

It's an excellent book describing all the techniques you need to know for hard case GRP lay-up.

I find that PVA on it's own is a bit risky, and will hold your lay-up a bit too well. Use PVA in conjunction with a good non-silicone based wax (canuba).

You can purchase all of this when you get the rest of your materials.

If you decide to use Polyester resin for your model, bear in mind that it pongs to high heaven. This isn't a problem for me, as I have a workshop, and I quite like the smell of polyester resin (I know I'm a strange bloke). But if you're making your model in the house and you have a Missus, be prepared for some domestic friction. Epoxy resins are far less pungent, but they are very expensive to purchase in this country, and in my view the cost to performance ratio doesn't justify the price.

You can make the basic plug from anything you have to hand. A lot of people use foam because it's easy to work and light. It's also quite cheap.

However you can use timber, plaster, metal or plastics to make your plug, it only has to be strong enough to withstand the handling involved with moulding. Use what ever method you feel most comfortable with.

Regarding getting the plug perfect. Obviously the better you can get it, the better the finished mould will be, but you don't have to be too fussy, unless you are producing kits, as any blemishes can easily be sanded out or spot filled when you are building it up.

The main thing to avoid is undercuts, which will result in nasty lock-ins. Again this is explained in the book. If you mould in rubber, undercuts are less of an issue, this is one of the reasons a lot of modelmakers use rubber tooling, especially when the model exhibits a lot of fine detail like plate lines and rivets. Rubber tooling also requires virtually zero preperation, i.e. no polishing and PVA'ing.

As you're interested in a TB4, a hard case mould is ideal for a simple shape like that, and much cheaper than using rubber. You can use GRP for the mould, or you can use plaster. If you go for the latter, use a special tooling plaster. Tiranti sell a plaster called 'Pure Alpha', and it's excellent. It has a very high exotherm, and sets off in minutes. You can comfortably demould in about two hours, although I prefer to leave things overnight, just to be sure.

An extra thing I always fit on any mould, are small holes where I can insert compressed air. This makes mould release a quick and painless task. Before lay up, I fill the holes with little pieces of plasticene. This stops the gelcoat from leaking through, but easily blows out with the mould when the air is introduced.

I have a compressor to supply the air, but you can use a footpump, or even a bicycle pump. Much easier than using little wooden wedges, believe me!

You will end up with some little dimples on your work where the air holes were, I just sand them out (takes seconds).

The main thing to bear in mind is, NEVER EVER skimp on the polishing and PVA'ing on your mould before lay-up. Else it'll all end in tears. The prep is everything.

One last thing, mould something small and inconsequential first. Carve a little skiff or something, and practice the techniques on that. If you get it wrong, no big deal.

Andy

[clive]

Thanks

Many thanks for your replies, it has been very useful getting other peoples thoughts on this matter.

As Andy suggested I have ordered the Glass Fibre Handbook because although I worked in a fibreglass shop when I was an apprentice I have no doubt that much has changed with the passage of years.

[Guest]

If you've worked with fibreglass

If you've worked with fibreglass before, then I don't think you'll have too many problems. I don't think things have changed since GRP came into being in the '50's.

You can make a model using the lost foam method, which effectively entails laying the GRP over a foam plug, melting the foam out and then finishing the exterior off with either top/flow coat or polyester filler and plenty of elbow grease with the wet and dry.

The disadvantage with this approach, is

1. You have jut the one model- the plug is destroyed in the process.

2. Can be a bit messy

3. Tends to lead to a rather thick composite.

Whatever you go with, make sure you consolidate the glass and resin with a 'washer roller'. I made my own, as the ones supplied by CFS were too wide for my application.

Andy

[anonymous]

Hi Clive,
I made my R

Hi Clive,
I made my R class by the lost foam method i.e hardboard frames with foam sandwiched between. Fibreglass then laid up on this. It was described in the AMS magazine a few years back.

In retrospect, I wouldn't do it this way again and I would go the female mould route.

I thought it would be quicker but in fact fibreglass is hard to sand down compared with plaster etc. I also ended up making a female mould anyway because I wanted to be able to make another hull if the sub was lost or damaged.

David

[Guest]

Sub lost? With your pinger,

Sub lost? With your pinger, Dave. Surely not!

Andy

[anonymous]

Touche! (I think that should

Touche! (I think that should be an "e acute")

I'm a belt and braces type of engineer and if things can go wrong they will!

Actually I think I did the female mould beore the Pinger was developed
- in my defence.

And you'll be pleased to know that I've dropped all " dissolving aspirins", "little floats and reels" etc from my subs.

David