How to Make a Plug for a Fiberglass Mold

[Ray Barnes]

I'm going to try and make a mold this winter for my 88 Miller High Life (Circus Circus). I have never done this and was wonder what material to use for the plug (foam,bass wood, balsa,etc.). Also is there any tricks to make it symetrical. I have seen some post on doing the layups but can't find anything on making the plugs. The "search" option keeps timing me out.

 

[tnrcboatracer]

You've got to make it verwy, verwy carefulwy.........Seriously, making the plug takes the most time. I was following a thread of a guy making a 1/6 scale SR71 airplane plug, and subsequently mold; and he had 2-3 YEARS in the plug. THe last I saw, this summer he was finally pulling parts from the mold. I believe he started the plug in 2003. THe mold can only be as good as your plug........

 

[Terry Keeley]

I like kledgecell foam finished with a layer of light cloth...

 

[Mark Poole ModVP]

Such a project will take a lot of patience. Since this is your first time I would suggest you make a "practice" plug and mold for something a lot more simple in shape than a 1/8 scale hydro just for the purpose of teaching yourself the proper technique before you embark on making the hydro. If you are planning on making a hull and deck mold then you must decide what type of joint/seam it will be. An overlap type joint will have to be factored in for both top and hull molds so that when joined they are a close fit. I have found the best way for me to keep it all within specs is to build the plug on a symetrical "baseplate" that has perfect square corners and a marked centerline from which all measurments are checked against. I have been down this road and it took me several molds and a few mistakes to get to where I could do this with total confidence. Everyone has their own little tricks to get from a drawing to a finished product.

Mark

 

[Ray Barnes]

Thanks for the advice. I'll take it slow. The worst that could happen is I will have to scrap it and buy a cowl that is already done.

I should have posted this first. I only plan on making the cowl for now.

Terry, Where do I get this foam?

 

[rhomodel]

You can use any material for the plug, as long as you seal and smooth it properly.

 

[Mike Broad]

No need to spend 2 or three years on the project. Use a spray putty on the plug and rub down with wet and dry paper (fine). Use a good release agent, there are many on the market that are far better the slip wax. Bear in mind if you only anticipate using the mould once or twice. It may be easier to fine finish the moulded object than spend hours on the plug.

Mike Broad

 

[SayMikey]

No need to spend 2 or three years on the project. Use a spray putty on the plug and rub down with wet and dry paper (fine). Use a good release agent, there are many on the market that are far better the slip wax. Bear in mind if you only anticipate using the mould once or twice. It may be easier to fine finish the moulded object than spend hours on the plug.
Mike Broad

http://www.info-central.org/construction_moldmaking.shtml

 

[tnrcboatracer]

It is very hard for a cast rubber mold to hold any kind of tolerance.

 

[SayMikey]

It is very hard for a cast rubber mold to hold any kind of tolerance.

If your only doing 1 or 2 a plaster cast will work. you can buy it cheap Charles Perdue can tell you his process

 

[tnrcboatracer]

It is very hard for a cast rubber mold to hold any kind of tolerance.

If your only doing 1 or 2 a plaster cast will work. you can buy it cheap Charles Perdue can tell you his process

The Ultracal gypsum cement is very similar to plaster. Someone has a bunch of pics in the gallery of a SP40 they made this way. I forget who had that photo series, it may have been Charles.

Mike Broad, If you had seen the SR71 photo essay, you would understand why it took that long. It is going to be a $25K~$50k twin turbojet model airplane. It is perfect scale.

 

[tnrcboatracer]

Here is the link to the SR71 Project. He had just short of 4 years on the plug, and another 12 months on the mold. He started this project in Jan 2002. The plug was finished around Dec 2005, and the mold complete in Dec 2006. This project in incredible!