Fibreglass (glass fiber) mould question

[nrg710]

I am about to embark upon building a 1:87 model of RMS Titanic. That will make the hull just over 3m (10ft) long. My intention is for it to be RC and lit. I also want it to be up there with the best models of this ship.

 

I have toyed with the idea of plank on frame construction for the hull, but because of certain limitations, I'm looking into other methods and I'm pretty set on the idea of CNC cutting a mould. The hull would then be constructed in the mould out of fibreglass.

 

Questions are:

- what's a good material to make the mould out of?

- will any external details that are CNC cut in the mould be replicated on the finished surface of there fibreglass? In other words, how good is the resin at preserving intricate details in the mould?

[AntonyUK]

Hi.

The mould needs to have a very rigid base to hold the shape.

Something that long will twist out of shape very quickly when laminating.

Because you will seal the mould you can use most materials as long the sealer you use does not destroy the mould.IE foam.

And every little imperfection you build into the mould will show. Really every little hairline will show.

The method would be -:

You build a timber hull with as much details as you require.

Then I would cast a plug out of the hull you just built.

Then you can cast your working piece.

 

But I would make a plywood on bulkhead model as the main parts of the ship you could use plywood as there no compound curves on the Titanic.

Why RC it... Sit in it and enjoy

 

That's my thoughts on such a large model.

Regards Antony.

Edit spelling...

Edited January 24, 2014 by AntonyUK

[NMBROOK]

Hi

This sounds like a project and a half.If you hace full cnc facilities for something of this size and obviously you won't be building something like this on a shoestring budget,I would machine the hull out of pattern making clay(the same thing used by car design developers)and then produce a two(minimum) piece mould out of fibreglass,then produce a hull from this mould.To maintain the detail on the hull so it is less prone to chipping I would only use epoxy resins NOT polyester which isn't as durable.The mould wall should be a minimum of 2.5 times the thickness of the the hull you will be producing.The mould will need extensive reinforcement to prevent distortion from the exothermic reaction(big deal at this size).At this scale I would consider moulding a subdeck from fibreglass so this can be 'glassed' to the hull to improve torsional stiffness.You deck planking could then be laid on top.To recoup your costs,you could offer further hulls for sale as to my knowledge,nobody has anything like this on the market.

 

Kind Regards Nigel

Edited January 24, 2014 by NMBROOK

[nrg710]

Thanks for the replies guys.

 

I'd already figured this wasn't going to be a cheap way of doing it! However, I figure that it would take me about a year to come up with a conventional plank-on-frame hull with all the shell plating/riveting etc, whereas (in theory) I could have a hull in less than a week given the CNC route. And if anyone ever wanted a 1/87 scale RMS Titanic (or RMS Olympic or Britannic) hull, then yes... I'd happily sell them one. There is a guy in the US who makes 1:144 RMS T. hulls out of fibreglass- I'm guessing he has done something like this.

 

I have a "tame" CNC fabrication company who has done some work for me in the past, so this is who I'd probably use. They don't charge an arm and a leg for machine time, providing that you're not in a hurry for your product and it can fill gaps between "proper" jobs. The guy who owns the company suggested I use aluminium for the mould, which originally I was sceptical about- mainly because a mould of this size will be really quite heavy.

 

I'd already envisaged splitting the mould into at least 9 pieces- this is mainly to reduce the amount of material that would be purchased for machining. It would also have the advantage of reducing machining time (although set-up time would be increased).

 

I'm intrigued about pattern forming clay- I've not heard of this before and a brief search on Google doesn't enlighten me. What is it, where can I get it from, and what are its sort of properties?

[NMBROOK]

Unfortunately I have only seen it on tv on documentaries,however a billet ali mould would without question be superior to anything else that is normally used for this process.It would actually act as a heatsink to prevent the resin from getting to warm whilst curing!Selling hulls is a very viable option,I have seen one guy selling large Bismarck hulls on the net to cover his initial development and mould costs.Failing that a company that actually sells fibreglass hulls may purchase the moulds from you as I can see this being quite a relatively popular(for a hull of this size) project.I can understand your reasoning going for HO scale regarding figures,but if you are planning on selling hulls,you need to weigh up 1/87 vs 1/72 for the availability of aftermarket ship fittings

 

Kind Regards Nigel

[dgbot]

Years ago several club members were asked to build an aircraft carrier.  They used builders foam for the plug.  Very strong and durable.  After the fiberglassing was done just use a little acetone and melt the foam out.

David B

[nrg710]

@Nigel, I haven't considered 1/72, mainly because I'm building it for a model railway layout! My intention is that it will sit as the "centrepiece" of a New York Docks style model railway.

 

I'm in two minds about whether to make this a model of RMS Titanic as built by Harland & Woolff in 1911/12, or whether to make this a model of that as built by CNC Jinling. i.e., Clive Palmer's Titanic 2.

 

The biggest problem I have at the moment is actually computing power. To create the mould, there's a lot of graphics that need to go into Solidworks and my little laptop isn't handling it very well!

[NMBROOK]

That explains everything,understandable,that is going to be one BIG layout!!!!!

 

Kind Regards Nigel

[nrg710]

Yes! The next house that I move to is going to have a garage that will be given over to... things that aren't cars. I've no time for cars.

 

Anyway, back on topic... if I create a mould for fibreglass and that mould has lots of details in it (rivets, shell plating, marks for where sidelights will be drilled), how well will the fibreglass cast hold these details?

 

Regarding rigidity, I'm not worried about that. I'm designing an internal structure that will support the ship's own weight and give a little to torsion moments. Such is the beauty of solidworks... In fact, if I get the add on (simulationworks) I can even spot stress points before I build it and then design them out!

[NMBROOK]

If you stick with epoxies and avoid polyesters,the detail will be durable and crisp.Most fibreglass model hulls use polyurethane resins which reproduces the detail but can be prone to chipping.With a hull of this size I would go for max durability.Yes the resins are more expensive but I think worth it in the long run

 

Kind Regards Nigel

[nrg710]

Thanks Nigel

 

I'm going to build a "trial" mould for another [smaller] ship out of wood and line in with aluminium high speed tape for the detailing. Will let you know how I get on!